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10.8: Case Study Conclusion: Pressure and Chapter Summary - Biology

10.8: Case Study Conclusion:  Pressure  and Chapter Summary - Biology


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Case Study Conclusion: Under Pressure

As you learned in this chapter, the human body consists of many complex systems that normally work together efficiently like a well-oiled machine to carry out life’s functions. For example, Figure (PageIndex{1}) illustrates how the brain and spinal cord are protected by layers of membrane called meninges and fluid that flows between the meninges and in spaces called ventricles inside the brain. This fluid is called cerebrospinal fluid (CSF) and as you have learned, one of its important functions is to cushion and protect the brain and spinal cord, which make up most of the central nervous system (CNS). CSF additionally circulates nutrients and removes waste products from the CNS. CSF is produced continually in the ventricles, circulates throughout the CNS, and then is reabsorbed by the bloodstream. If too much CSF is produced, its flow blocked, or if not enough is reabsorbed, the system becomes out of balance, and CSF can build up in the ventricles. This causes an enlargement of the ventricles called hydrocephalus that can put pressure on the brain, resulting in the types of neurological problems that former professional football player, Dayo, described at the beginning of this chapter, is suffering from.

Recall that Dayo’s symptoms included loss of bladder control, memory loss, and difficulty walking. The cause of their symptoms was not immediately clear, although their doctors suspected that it related to the nervous system since the nervous system acts as the control center of the body, controlling and regulating many other organ systems. Dayo’s memory loss directly implicated the involvement of the brain, since that is the site of thoughts and memory. The urinary system is also controlled in part by the nervous system, and the inability to hold urine appropriately can be a sign of a neurological issue. Dayo’s trouble walking involved the muscular system, which works alongside the skeletal system to enable movement of the limbs. In turn, the contraction of muscles is regulated by the nervous system. You can see why a problem in the nervous system can cause a variety of different symptoms by affecting multiple organ systems in the human body.

To try to find the exact cause of Dayo’s symptoms, their doctors performed a lumbar puncture, or spinal tap, which is the removal of some CSF through a needle inserted into the lower part of the spinal canal. Doctors then analyzed Dayo’s CSF for the presence of pathogens such as bacteria to determine whether an infection was the cause of their neurological symptoms. When no evidence of infection was found, Doctors used an MRI to observe the structures of Dayo's brain. This is when Doctors discovered Dayo's enlarged ventricles, which are a hallmark of hydrocephalus.

To treat Dayo’s hydrocephalus, a surgeon implanted a device called a shunt in Dayo's brain to remove the excess fluid (Figure (PageIndex{2})). One side of the shunt consists of a small tube, called a catheter, which was inserted into Dayo’s ventricles. Excess CSF is then drained through a one-way valve to the other end of the shunt, which was threaded under their skin to their abdominal cavity, where the CSF is released and can be reabsorbed by the bloodstream.

Implantation of a shunt is the most common way to treat hydrocephalus, and for some people, it can allow them to recover almost completely. However, there can be complications associated with a brain shunt. The shunt can have mechanical problems or cause an infection. Also, the rate of draining must be carefully monitored and adjusted to balance the rate of removal of CSF with the rate of its production. If it is drained too fast, it is called overdraining, and if it is drained too slowly, it is called underdraining. In the case of underdraining, the pressure on the brain and associated neurological symptoms will persist. In the case of overdraining, the ventricles can collapse, which can cause serious problems such as the tearing of blood vessels and hemorrhaging. To avoid these problems, some shunts have an adjustable pressure valve where the rate of draining can be adjusted by placing a special magnet over the scalp. You can see how the proper balance between CSF production and removal is so critical – both in the causes of hydrocephalus and in its treatment.

In what other ways does your body regulate balance, or maintain a state of homeostasis? In this chapter, you learned about the feedback loops that keep body temperature and blood glucose within normal ranges. Other important examples of homeostasis in the human body are the regulation of the pH in the blood and the balance of water in the body. You will learn more about homeostasis in different body systems in the coming chapters.

Thanks to Dayo’s shunt, their symptoms are starting to improve, but they have not fully recovered. Time may tell whether the removal of the excess CSF from their ventricles will eventually allow them to recover normal functioning or whether permanent damage to their nervous system has already been done. The flow of CSF might seem simple but when it gets out of balance, it can easily wreak havoc on multiple organ systems because of the intricate interconnectedness of the systems within the human “machine."

Chapter Summary

This chapter provided an overview of the organization and functioning of the human body. You learned that:

  • The human body consists of multiple parts that function together to maintain life. The biology of the human body incorporates the body’s structure, or anatomy, and the body’s functioning, or physiology.
  • The organization of the human body is a hierarchy of increasing size and complexity, starting at the level of atoms and molecules and ending at the level of the entire organism.
  • Cells are the level of organization above atoms and molecules, and they are the basic units of structure and function of the human body. Each cell carries out basic life functions as well as other specific roles. Cells of the human body show a lot of variation.
    • Variations in cell function are generally reflected in variations in cell structure.
    • Some cells are unattached to other cells and can move freely; others are attached to each other and cannot move freely. Some cells can divide readily and form new cells; others can divide only under exceptional circumstances. Many cells are specialized to produce and secrete particular substances.
    • All the different cell types within an individual have the same genes. Cells can vary because different genes are expressed depending on the cell type.
    • Many common types of human cells consist of several subtypes of cells, each of which has a special structure and function. For example, subtypes of bone cells include osteocytes, osteoblasts, osteogenic cells, and osteoclasts.
  • A tissue is a group of connected cells that have a similar function. There are four basic types of human tissues that make up all the organs of the human body: epithelial, muscle, nervous, and connective tissues.
    • Connective tissues, such as bone and blood, are made up of cells that are separated by non-living material, called the extracellular matrix.
    • Epithelial tissues, such as skin and mucous membranes, protect the body and its internal organs and secrete or absorb substances.
    • Muscle tissues are made up of cells that have the unique ability to contract. They include skeletal, smooth, and cardiac muscle tissues.
    • Nervous tissues are made up of neurons, which transmit electrical messages, and glial cells of various types, which play supporting roles. Types of nervous tissues include gray matter, white matter, nerves, and ganglia.
  • An organ is a structure that consists of two or more types of tissues that work together to do the same job. Examples include the brain and heart.
    • Many organs are composed of a major tissue that performs the organ’s main function, as well as other tissues that play supporting roles.
    • The human body contains five organs that are considered vital for survival. They are the heart, brain, kidneys, liver, and lungs. If any of these five organs stops functioning, the death of the organism is imminent without medical intervention.
  • An organ system is a group of organs that work together to carry out a complex overall function. For example, the skeletal system provides structure to the body and protects internal organs.
    • There are 11 major organ systems in the human organism. They are the integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, digestive, urinary, and reproductive systems. Only the reproductive system varies significantly between males and females.
  • The human body is divided into a number of body cavities. A body cavity is a fluid-filled space in the body that holds and protects internal organs. The two largest human body cavities are the ventral cavity and the dorsal cavity.
    • The ventral cavity is at the anterior, or front, of the trunk. It is subdivided into the thoracic cavity and abdominopelvic cavity.
    • The dorsal cavity is at the posterior, or back, of the body, and includes the head and the back of the trunk. It is subdivided into the cranial cavity and spinal cavity.
  • Organ systems of the human body must work together to keep the body alive and functioning normally. This requires communication among organ systems. This is controlled by the autonomic nervous system and endocrine system. The autonomic nervous controls involuntary body functions, such as heart rate and digestion. The endocrine system secretes hormones into the blood that travel to body cells and influence their activities.
    • Cellular respiration is a good example of organ system interactions because it is a basic life process that occurs in all living cells. It is the intracellular process that breaks down glucose with oxygen to produce carbon dioxide and energy. Cellular respiration requires the interaction of the digestive, cardiovascular, and respiratory systems.
    • The fight-or-flight response is a good example of how the nervous and endocrine systems control other organ system responses. It is triggered by a message from the brain to the endocrine system and prepares the body for flight or a fight. Many organ systems are stimulated to respond, including the cardiovascular, respiratory, and digestive systems.
    • Digesting food requires teamwork between the digestive system and several other organ systems, including the nervous, cardiovascular, and muscular systems.
    • Playing softball or doing other voluntary physical activities may involve the interaction of nervous, muscular, skeletal, respiratory, and cardiovascular systems.
  • Homeostasis is the condition in which a system such as the human body is maintained in a more-or-less steady state. It is the job of cells, tissues, organs, and organ systems throughout the body to maintain homeostasis.
    • For any given variable, such as body temperature, there is a particular set point that is the physiological optimum value. The spread of values around the setpoint that is considered insignificant is called the normal range.
    • Homeostasis is generally maintained by a negative feedback loop that includes a stimulus, sensor, control center, and effector. Negative feedback serves to reduce an excessive response and to keep a variable within the normal range. Negative feedback loops control body temperature and blood glucose level.
    • Sometimes homeostatic mechanisms fail, resulting in homeostatic imbalance. Diabetes is an example of a disease caused by homeostatic imbalance. Aging can bring about a reduction in the efficiency of the body’s control system, making the elderly more susceptible to disease.
  • Positive feedback loops are not common in biological systems. Positive feedback serves to intensify a response until an endpoint is reached. Positive feedback loops control blood clotting and childbirth.

The severe and broad impact of hydrocephalus on the body’s systems highlights the importance of the nervous system and its role as the master control system of the body. In the next chapter, you will learn much more about the structures and functioning of this fascinating and important system.

Chapter Summary Review

  1. Compare and contrast tissues and organs.
  2. Osteocyte cells are part of which type of tissue and organ system?
  3. Adipose tissue, or body fat, is the same general type of tissue as:
    1. mucous membranes
    2. gray matter
    3. skin
    4. blood
  4. Which type of tissue lines the inner and outer surfaces of the body?
  5. True or False. The extracellular matrix that surrounds cells is always solid.
  6. True or False. Skin is an organ.
  7. What is a vital organ? What happens if a vital organ stops working?
  8. Name three organ systems that transport or remove wastes from the body.
  9. Name two types of tissue in the digestive system.
  10. For each of the following body functions, choose the organ system that is most associated with the function. Organ systems: integumentary; skeletal; muscular; nervous; endocrine; cardiovascular; lymphatic; respiratory; digestive; urinary; reproductive
    1. Processes sensory information
    2. Secretes hormones
    3. Releases carbon dioxide from the body to the outside world
    4. Produces gametes
    5. Controls water balance in the body
  11. The spleen is part of which organ system?
    1. Digestive
    2. Lymphatic
    3. Integumentary
    4. Urinary
  12. Describe one way in which the integumentary and cardiovascular systems work together to regulate homeostasis in the human body.
  13. Name the two largest body cavities in humans and describe their general locations.
  14. What are the names given to the three body cavity divisions where the reproductive organs are located?
  15. True or False. There are two pleural cavities.
  16. True or False. Body cavities are filled with air.
  17. The pituitary gland is in which organ system? Describe how the pituitary gland increases metabolism.
  18. When the level of thyroid hormone in the body gets too high, it acts on other cells to reduce the production of more thyroid hormone. What type of feedback loop does this represent?
  19. Hypothetical organ A is the control center in a feedback loop that helps maintain homeostasis. It secretes molecule A1 which reaches organ B, causing organ B to secrete molecule B1. B1 negatively feeds back onto organ A, reducing the production of A1 when the level of B1 gets too high.
    1. What is the stimulus in this feedback loop?
    2. If the level of B1 falls significantly below the setpoint, what do you think happens to the production of A1? Why?
    3. What is the effector in this feedback loop?
    4. If organs A and B are part of the endocrine system, what type of molecules do you think A1 and B1 are likely to be?
  20. What are the two main systems that allow various organ systems to communicate with each other?
  21. The hypothalamus is part of the:
    1. spinal cord
    2. thoracic cavity
    3. kidneys
    4. brain
  22. What are two functions of the hypothalamus that you learned about in this chapter?

Applied Mechanical Design

This book is the result of lessons, tutorials and other laboratories dealing with applied mechanical design in the universities and colleges. In the classical literature of the mechanical design, there are quite a few books that deal directly and theory and case studies, with their solutions. All schools, engineering colleges (technical) industrial and research laboratories and design offices serve design works. However, the books on the market remain tight in the sense that they are often works of mechanical constructions. This is certainly beneficial to the ordinary user, but the organizational part of the functional specification items is also indispensable.


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The Juxta CURES adjustable compression system for treating venous leg ulcers

A search of the Medicines and Healthcare Products Regulatory Agency (MHRA) website revealed no manufacturer Field Safety Notices or Medical Device Alerts for this equipment.No reports of adverse events were identified from searches of the US Food and Drug Administration (FDA) database: Manufacturer and User Device Facility Experience (MAUDE).

Clinical evidence

Thirty one studies were identified for this briefing, however 21 were excluded as they did not meet the inclusion criteria, while 1 study was excluded as it did not contain any quantitative data. Therefore 9 studies have been included in this briefing. Four of these are published case studies of 1–3 patients (Bianchi et al. 2013 Dowsett and Elson 2013 Lawrence 2014a Nugent et al.2013). Two publications also report cost savings (Bianchi et al. 2013 Nugent et al.2013). Four of the studies were only available as poster presentations the case report by Davies (2013) and the 3 case series by Elson (2012), Harris (2013) and Oates et al. (2013). Of these, Elson et al. (2012) also reported cost savings. Finally, 1 case series was available as an abstract only (Lurie et al. 2012). The details and results of these studies are reported in tables 1–9.

One study by Harris (2013) reported that 3 of the 14 patients in this study decided to change to an alternative compression bandaging system. Their reasons were cited as preference, management of lymphoedema, and a fall. It is unclear if these events were device related.

Table 1 Summary of the Bianchi et al. (2013) case reports

Study component

Description

To illustrate effective management using the Juxta CURES compression system.

Retrospective descriptive case reports on 3 patients.

Hospital, GP and community setting in the UK. Patients treated with the Juxta CURES 2012–13.

Venous disease of the lower limb.

Case 1: a 42-year-old female with a 4-year history of leg ulcers. The patient was not compliant with compression therapy and preventative hosiery, resulting in frequent ulcer recurrence often resulting in hospitalisation due to cellulitis. The patient was clinically obese and had type 2 diabetes and epilepsy. Her job required her to stand for long periods with no facility to sit or elevate her leg. She had normal ABPI, with a wound measuring 7.5 cm × 5.5 cm completely covered in slough. She was reluctant to use compression bandages due to the negative impact on body image, inability to wear attractive shoes, uncontrolled exudate and bandage bulk and slippage.

Case 2: a 48-year-old male with a 12‑month history of non‑healing VLUs (size of wound not stated). This is likely to be the same patient as described by Nugent (2013 table 8).

Case 3: a 65-year-old female with recurrent leg ulcers since her late 40s. She had worsening, extremely painful, continuous non‑healing ulcers on both lower legs for the last 5 years. She had type 2 diabetes, hypertension and hyperthyroidism and needed a knee replacement. Allergy to cetearyl alcohol prevented use of numerous topical creams. Difficulties with compression therapy caused uncontrolled venous hypertension leading to lymphovenous disease.

Case 1: The patient and practice nurses were trained in the use of the Juxta CURES.

Case 2: The Juxta CURES was applied at a pressure of 40 mmHg.

Case 3: The patient was admitted to hospital for 10 weeks of intensive wound management, including 4 weeks of intravenous antibiotics and multi‑layer lymphoedema bandaging. Ulcers were dressed with 7, 15 cm × 15 cm Aquacel dressings every other day, with 9 bandages applied at each dressing change. Oramorph was taken prior to dressing changes as analgesia, but she was comfortable between dressing changes and her legs improved rapidly. The Juxta CURES was prescribed to allow self-management on holidays while providing continued effective compression.

Case 1: Clinic appointments were reduced from alternate days to twice weekly. After 3 weeks the wound reduced in size to 5 cm × 3.5 cm and after a further 3 weeks was 3.5 cm × 1.2 cm with the wound bed showing 50% slough and 50% granulation. A further few weeks showed the wound had almost closed. The patient and practice nurse found the device easy to use, and compliance was no longer an issue.

Case 2: The wound had decreased in size by 50% by the fifth week, and the wound area to the lateral and posterior aspects had healed. By week 10 there was further healing in wound size with 3 remaining wounds to the anterior aspect. The patient found the Juxta CURES very comfortable to wear and the ability to wear shoes was a bonus. The treatment regime also showed a significant cost saving.

Case 3: The patient reported that she had stopped taking painkillers and had an improved quality of life. She could bathe, shower and dress her own legs. The patient reported that the Juxta CURES felt light to wear, unlike bandages which used to weigh her legs down she was also able to wear her own shoes. The Juxta CURES was reported to be easy to apply and took 30 minutes to apply, whereas conventional bandages had taken 1 hour.

Clinical experience using the Juxta CURES on less demanding ulcers has shown accelerated healing rates due to consistent compression. This is facilitated by a degree of self‑management from the patients.

Abbreviations: ABPI, ankle brachial pressure index VLU, venous leg ulcer.

Table 2 Summary of the Davies (2013) case report

Study component

Description

To evaluate the treatment of a painful leg ulcer with a novel compression device.

Retrospective descriptive case report.

Not stated. Patient treatment with the Juxta CURES commenced in 2013.

73-year-old male with a VLU on the left leg that had not healed in 18 months. Medical assessment and ABPI indicated the wound was suitable for compression bandaging therapy. Multi‑layer compression started in September 2011 but discontinued in October 2012 at patient request due to pain and sleep disturbance. The patient had a pain score of 10 at night (0=no pain, 10=worst pain) and was taking strong opiate analgesia and antidepressants.

The VLU was treated with the Juxta CURES, with pressure adjusted, if not tolerated, by the patient and could be removed at night when the pain was severe.

After 4 days the patient reported the device was comfortable and allowed him to sleep through the night. Oedema had reduced by 9 cm at the ankle and 6.5 cm at the calf. The wound appeared unchanged.

After 14 days the patient stated the treatment had transformed his life. The patient reported minimal pain levels (score 1–2) and no longer required regular analgesia antidepressants were also discontinued. Reduced pressure was maintained through the night. At 8‑week follow-up, the wound had healed.

This simple adjustable self-management compression device maintained the therapeutic levels of compression necessary day and night for the healing of venous leg ulcers thereby improving patient quality of life.

Abbreviations: ABPI, ankle brachial pressure index VLU, venous leg ulcer.

Table 3 Summary of the Dowsett and Elson (2013) case reports

Study component

Description

To assess whether quality-of-life issues could be addressed by treatment with the Juxta CURES.

Retrospective descriptive case reports on 2 patients.

Patients treated with Juxta CURES in a UK community setting between 2010 and 2012.

Case 1: a 47-year-old male with a 10‑year history of bilateral VLUs. A variety of compression systems had been used on his legs but he admitted non-compliance due to the impact on his employment caused by the need to take unpaid leave to attend clinic appointments. He was experiencing malodour, extreme pain and depression. When at home he spent his time lying on the bed elevating his legs as instructed by his nurse.

Case 2: a 63-year-old woman with a 42‑year history of VLUs. A variety of compression systems had been used and all of those required daily treatment due to bandage slippage or high exudate levels. Her 'inverted champagne bottle' shaped leg, with a large calf and a relatively small ankle circumference, proved complex to manage. The patient's quality of life was severely affected due to high levels of exudate and repeat episodes of cellulitis resulting in her becoming housebound. Her 30‑year‑old son left full‑time employment to become her carer.

Case 1: Patient applied the Juxta CURES, checked by the nurse at appropriate intervals.

Case 2: The Juxta CURES initially applied to the right leg and then also to the left leg with dressings changed once or twice a week as needed.

Case 1: After 8 months use of the Juxta CURES, the ulcer was completely healed. The patient's quality of life dramatically improved, his pain and depression disappeared and he resumed normal work.

Case 2: The Juxta CURES was applied to the patient's right leg as this was the least severely affected. The patient was pleased to be able to wear non-orthotic shoes. Swelling reduced and there were signs of improvement to the wound, and the patient asked for a second device for her left leg. Both legs continued to heal. Nursing time was reduced from 90 minutes per week to 20 minutes per week. The patient's condition improved to the point where she no longer needed a carer and her son could plan a return to work.

The Juxta CURES assisted in improving patient wellbeing while still maintaining therapeutic levels of compression.

Abbreviations: VLU, venous leg ulcer.

Table 4 Summary of the Elson (2012) case series

Study component

Description

To compare the costs of treating venous ulcers with compression bandages compared with the Juxta CURES.

A multicentre, prospective case series (17 patients).

17 patients, average length of time ulcer present = 7 years.

Each clinician recorded 6 months of data of standard compression therapy and 6 months of Juxta CURES use including:

type and number of wound dressings used

compression bandaging type and number used.

During 6 months of treatment with standard care before testing the new device, all ulcers remained static or deteriorated.

Where the patient had not used the compression garment for 6 months an estimate was made. This data was used to calculate and compare the costs of the 2 treatment options.

After 6 months of treatment with the Juxta CURES all patients showed improvement in the condition of their leg ulcers. Patients and clinicians all gave positive feedback. Other results are summarised in the 'published cost studies' section.

The Juxta CURES proved cost effective when compared to standard compression bandaging, with improved leg ulcer condition at significantly lower cost.

Table 5 Summary of the Harris (2013) case series

Study component

Description

Using the Juxta CURES can eliminate issues associated with leg ulceration and provide the clinician with an easy alternative. It can improve quality of healthcare and reduce costs.

Retrospective descriptive case series of 14 non‑consecutive patients.

Community setting – 7 patients seen in the leg ulcer clinic, 7 patients seen at home.

9 patients with venous leg ulcers, 5 patients with leg ulcers of mixed aetiology (one patient had ulcers on both legs). Duration of leg ulceration ranged from new onset to 2.5 years.

A mix of new patient referrals and patients already having conventional compression therapy. All patients were offered the Juxta CURES with compression levels ranging from 20 mmHg to 40 mmHg as suited to their ABPI and clinical presentation.

All patients experienced improvements in their wounds and in skin integrity. The system was tolerated by 11 patients at the same or higher compression than previously used and 3 patients changed to alternative compression systems. Five patients' wounds progressed to healing in the 10‑week study period, and 4 were able to self–manage, resulting in reduced nursing time. Three chose to keep using the Juxta CURES after healing.

Clinicians particularly valued being able to accurately measure the compression levels through the built-in pressure measurement system. 96% of clinicians reported the fit, ease of application, application time and use of the built-in pressure system as very good or excellent. Clinicians reported reduced nurse time applying the Juxta CURES compared to conventional compression bandaging. A cost saving was realised after 12 weeks use of Juxta CURES in replacement of compression bandaging. Over 6 months use there was a cost saving of £2141 per patient.

Improved quality of life and wound healing was seen in 12 out of 14 patients. The Juxta CURES provided patients and clinicians with solutions to the problems associated with conventional compression therapy. Use of the Juxta CURES promoted self-care and resulted in financial savings compared to conventional compression bandaging, and a reduction in materials (for example, bandaging), nurse time and clinical waste.

Abbreviations: ABPI, ankle brachial pressure index n, number of patients.

Table 6 Summary of the Lawrence (2014a) case reports

Study component

Description

To illustrate how finding a compression regime that individuals can adopt without discomfort while being able to wear their usual footwear is important for many patients, and this can help maintain mobility and improve concordance.

Retrospective descriptive case reports on 3 patients.

Community setting in the UK.

Case 1: a 52-year-old woman with a 10‑year on–off history of VLUs and normal ABPI. She had self‑treated for almost 2 years before referral with a VLU measuring 8 cm x 5 cm.

Case 2: a 33-year-old morbidly obese man with a 6‑month ulcer history and normal ABPI. On examination, venous disease and associated oedema were present. Initial ulcer measurement was 12 cm × 10 cm the ulcer was superficial with a low exudate level.

Case 3: an 82-year-old man with bilateral weeping oedematous legs and feet and 2 ulcers on his left leg. The patient also had type 2 diabetes and poor mobility caused by osteoarthritis and previous ankle injury and exacerbated by pain from leg ulcers. He also suffered peripheral vascular disease, foot neuropathy and reduced ABPI: 0.64 (left leg) and 0.75 (right leg).

Case 1: 4-layer compression bandaging at 40 mmHg was applied for approximately 1 month, during which time the patient was unable to wear footwear suitable for her employment and lost her job. New work commitments meant she became unable to attend clinics and the ulcer remained static. Therefore the Juxta CURES was considered as the patient could learn how to change her own dressings and reduce clinic visits. It was used after dressing with Aquacel foam and Cavalon No Sting Barrier was used to protect the periulcer area.

Case 2: Bandages were applied, but proved difficult due to leg shape. 4‑layer and 2‑layer methods were trialled but removed by the patient due to slippage and discomfort. These bandages also made wearing a suit and dress shoes difficult and bandage slippage was embarrassing to the patient. The patient also reported malodour which he attributed to infrequency of dressing changes. The limb was too large for compression hosiery and the Juxta CURES was used to provide compression with Atrauman dressings.

Case 3: Reduced compression was prescribed but was painful, especially over the left ankle which had metal implants following a previous injury. Even highly absorbent dressings became saturated with exudate within a day and needed changing. Compression was stopped and replaced with the Juxta CURES at 20 mmHg with Aquacel dressings which the patient was able to tolerate.

Case 1: The patient was able to self-manage the Juxta CURES bandages whilst still working and attended clinics when possible. The wound reduced in size to 2 cm x 2 cm (time period not stated).

Case 2: The patients' ulcer responded well, healed completely and had remained healed at 12 months follow‑up. Off‑the‑shelf standard compression stockings were provided for maintenance.

Case 3: The Juxta CURES required frequent readjustment over the first 2 days to maintain a good fit whilst the oedema reduced rapidly. The ulcers still remained at the time of reporting, but oedema and wetness had resolved. The patient tried to use compression hosiery on his right leg again but weeping resumed so he continued with the Juxta CURES to maintain skin integrity.

The Juxta CURES is useful for patients with large lower limbs and narrow ankles who struggle with bandage and hosiery slippage. It is beneficial for patients who wish to self‑treat or are unable to attend regular clinic appointments. It provides and maintains therapeutic compression at the desired, measurable level. Patients find it comfortable to wear and it could help improve compliance with treatment.

Abbreviations: ABPI, ankle brachial pressure index n, number of patients

Table 7 Summary of the Lurie et al. (2012) case series

Study component

Description

To determine the suitability of the Juxta CURES as a compression device for the treatment of VLUs.

Retrospective descriptive case series of 10 non‑consecutive patients.

Clinician and patient satisfaction and therapeutic effectiveness.

8 male, 2 female patients aged between 26 and 92 years.

Patients wore the Juxta CURES over an appropriate wound dressing and a sock liner in combination with a compression anklet for the foot. Regular check-ups and wound dressing changes were undertaken. 8 patients wore the device all day every day 2 patients wore the system continuously for 1 week and then for 12 hours during the day, every day thereafter.

2 patients withdrew due to unrelated causes. The ulcers of the remaining 8 patients all healed in an average of 66 days after starting use of the Juxta CURES.

Clinicians found the Juxta CURES easy and quick to fit and remarked that it provided a good fit. Patients reported it was comfortable to wear, controlled swelling and allowed maintenance of hygiene. Clinicians evaluated the change in patients' oedema and skin, patient compliance and overall ulcer healing as excellent.

Abbreviations: n, number of patients VLU, venous leg ulcer.

Table 8 Summary of the Nugent (2013) case report

Study component

Description

To demonstrate how the Juxta CURES has had a positive impact on the patient's quality of life.

Retrospective descriptive case report.

Community setting in the UK.

Positive impact on patient quality of life.

A 48-year-old man with a 12‑month history of a non‑healing ulcer 20 cm × 10 cm which, although extensive, was fairly superficial. The patient was classed as non‑concordant as he declined to attend appointments because they clashed with his work schedule. This is likely to be the same patient as described in the study by Bianchi (2013).

The patient started self-managing his wound care in November 2012. Initially he used a 2‑layer compression system. This was changed to the Juxta CURES in November 2012, as the tissue viability nurse had concerns about the correct level of compression being reached at each application. The Juxta CURES was used in combination with a skin care and dressing regime comprising of Cetraben emollient cream and DryMax EXTRA. The patient was shown how to apply the Juxta CURES and use the built-in pressure system to ensure the correct level of compression (40 mmHg) was maintained throughout the week between appointments.

After 1 week the patient reported that the device was comfortable and easy to use. After 3 weeks wound size had reduced significantly, although there were signs of overgranulation. By week 5 the wound size had decreased by 50%, the wound area to the lateral and posterior aspects had healed and the overgranulation had settled. At week 7, 4 superficial granulating areas remained. Further improvement was seen at week 10, when just 3 superficial granulating areas remained and these measured 3 cm × 2.8 cm, 1.4 cm × 1.6 cm and 2.9 cm × 1.9 cm.

The patient enjoyed being in control of the wound management process and knowing that, if there was odour from the wound, he could shower and change the dressing. The ability to wear his own shoes was a bonus.

Use of the Juxta CURES had a positive impact on the patient, and he found using the device a positive experience.

Abbreviations: n, number of patients.

Table 9 Summary of the Oates et al. (2013) case series

Study component

Description

To enable patients to continue gold standard compression therapy treatment while allowing a higher degree of independence.

Case series (unclear if prospective or retrospective).

Patients with venous leg ulceration currently being treated with compression bandages were invited to change to the Juxta CURES.

The study reported a measurable reduction in wound size and leg oedema, improved patient concordance and wellbeing and a heightened sense of achievement for the nurses managing the patient. Costs and nursing time were noticeably reduced. Patient concordance was found to be much higher with the Juxta CURES than with comparable bandaging systems. Ease of use, the ability to reduce the pressure at night and to remove the device to take a shower being among the perceived benefits. The enhanced possibilities for patient self‑management also resulted in a lower number of district nurse visits being needed, bringing further reductions in cost.

The use of the device delivered significant benefits for both patients and staff in terms of better concordance, clinical effectiveness and cost reduction.

Abbreviations: n, number of patients.

Recent and ongoing studies

A UK study of 36 patients treated with the Juxta CURES has recently been completed. This data is expected to be published in May 2015.

Costs and resource consequences

In 2014 approximately 3,000 Juxta CURES devices were dispensed on prescription, with 86% of these prescribed by primary care clinicians and 14% by secondary care clinicians. The device has been used in approximately 15 locations across the NHS in England and is also used in leg clubs in Wales. The use of the Juxta CURES would not require any change to existing NHS facilities and would fit into the current care pathways, and can be prescribed on an FP10 prescription.

Current guidelines advise that standard compression therapy should only be applied by staff with appropriate training (RCN 2006 SIGN 2010), but the level of training needed is not specified. A standard pathway for prescribing compression therapy is also not specified.

Although the device has a higher acquisition cost than traditional compression bandages, it is anticipated that over the 6‑month minimum life‑span of the product, cost savings may be seen in the reduction of clinician time (reduced numbers of home or clinic visits and shorter visits), reduced amount of dressings and bandages needed and a resultant reduction in clinical waste.

Published cost studies

A case report on 3 patients (Bianchi et al. 2013) reported cost savings with the Juxta CURES compared with conventional bandaging over a 6‑month period. This was based on an evaluation of 17 patients and illustrated costs in 3 areas:

dressings: average saving of £753 per patient

bandages: average saving of £881 per patient

clinician time: average saving of £3172 per patient.

This would equal a total average saving of £4806 per patient. The study suggests that the use of the Juxta CURES results in reduced exudate, meaning that expensive extra‑absorbent dressings are not needed. Its use also appears to be cheaper than repeat bandaging and reduces clinical waste. The reduction in clinician time arises from faster application during clinic visits and a reduction in the number of clinic and home visits as the patient is encouraged to self-manage their care. The timeframe for this saving is not specified but is assumed to be over the course of 6 months. The source of these costs savings is not specified.

A poster presentation by Elson (2012) contained a product evaluation to compare the cost of treating venous ulcers with compression bandages with the Juxta CURES. Clinicians treating 17 patients recorded 6 months of data using standard compression therapy and 6 months using the Juxta CURES. Where the patient had not used the compression garment for 6 months an estimate was made. The data recorded included:

type and number of wound dressings used

compression bandaging type and number used.

The data were used to calculate and compare the costs of the 2 treatment options. These costs are detailed below in table 10.

Table 10 Summary of the cost evaluation from Elson (2012)

Costs associated with the care of 17 leg ulcer patients

Average cost

Dressings under compression

Standard compression treatment

Treatment with the Juxta CURES

Standard compression treatment

Treatment with the Juxta CURES

Standard compression treatment

Treatment with the Juxta CURES

Using these calculations, total included costs for standard care are £6570 and £1762 for the Juxta CURES. This would provide an average saving of £4808 for the 17 patients equating to £282.82 per patient. The timeframe for this saving is not specified but is it assumed to be over a 6‑month period. The sources of costing prices are not specified.

Harris (2013) reported that a positive cost saving was realised at week 12 after the initial outlay to purchase the Juxta CURES.

A case report by Nugent (2013) detailed treatment of a patient treated with the Juxta CURES, whose ulcer was previously treated unsuccessfully with compression bandages. The cost of the previous 12‑months' treatment before assessment prior to use with the Juxta CURES was calculated at over £3300 with no healing of the ulcer. After reassessment and commencement of the Juxta CURES, the ulcer reached an almost‑healed state before reporting at an estimated cost of £732. The time period for this estimated cost is not stated but is assumed to be for the 10 weeks during which the patient was treated with the Juxta CURES.

Strengths and limitations of the evidence

The identified evidence for the clinical effectiveness of the Juxta CURES was very limited in both quantity and quality, and comprised published case reports, abstracts and poster presentations. No large‑scale studies, or robust comparative data were identified.

All of the included studies involved small numbers of patients (the maximum specified was 17). Five studies (Bianchi et al. 2013 Davies 2013 Dowsett and Elson 2013 Lawrence 2014a Nugent et al. 2013) are case studies of 3 patients or fewer, and therefore it can be assumed that the outcomes of these studies should not be generalised.

It is unclear whether patients in the identified studies were enrolled consecutively this raises concerns about selection and attrition bias. Five studies are not reported in full, and are available only as posters or abstracts and have not undergone peer review. This includes the 4 case series (Elson 2012, Harris 2013, Lurie et al. 2012 and Oates et al. 2013). Inclusion and exclusion criteria are not clearly stated for these case series, and only Lurie et al. (2012) state primary outcomes. The lack of available detail means that these results should be treated with caution.

It is highly likely that the patient reported by Nugent (2013) is the same as 1 patient reported in the Bianchi et al. (2013) paper, of which Nugent is a co‑author.

Seven of the 9 studies contain acknowledgements to medi UK or have authors employed by medi UK or CircAid.

Economic reporting is limited and the sources of the costs and assumptions made are not specified, therefore it is not possible to assess their appropriateness. Variability of the cost saving between each study suggests that these results may not be generalisable. However all reports suggest the device is cost saving compared to compression bandaging.


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Here is a plot of (F) for the male height data:

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Design

Videofluorography was performed on 13 healthy subjects eating 6-g squares of banana, tofu, and cookies. Measurements included the number of St2Tr cycles, duration of processing (from food entering the mouth to onset of swallowing), pre-upper esophageal sphincter (UES) transit duration (from onset of swallowing to onset of UES transit), UES transit duration (leading edge to trailing edge passing the UES), and total sequence duration (from onset of swallowing to terminal swallow). Principal component (PC) analysis was used to identify factors affecting the number of St2Tr cycles. Analysis of covariance was performed using the 1st PC as an independent variable for predicting the number of St2Tr cycles.

Results

All four duration measures were significantly positively correlated with the number of St2Tr cycles. Analysis revealed two orthogonal PCs with variable loading. The 1st PC was a function of the timing variables. The 2nd PC was a function of the number of swallows.

Conclusions

The number of St2Tr cycles was associated with measures of food transit duration and was greater with harder foods before processing and more viscous foods just before swallowing.


Safety and loss prevention professionals process and plant engineers environmental and chemical safety professionals in all chemical, petroleum and process industry sectors

Preface to Fourth Edition

Preface to Second Edition

1.2 Industrial Safety and Loss Trends

1.3 Safety and Environmental Concerns

1.5 Large Single-Stream Plants

1.9 Total Quality Management

1.11 Safety-Critical Systems

1.12 Environment and Sustainable Development

1.14 Academic and Research Activities

Chapter 2. Incidents and Loss Statistics

2.2 Standard Industrial Classification

Chapter 3. Legislation and Law

3.2 US Regulatory Agencies

3.4 Occupational Safety and Health Act 1970

3.5 US Environmental Legislation

3.6 US Toxic Substances Legislation

3.7 US Accidental Chemical Release Legislation

3.8 US Transport Legislation

3.9 US Security Legislation

3.10 US Developing Legislation

3.14 US Chemical Safety Board

Chapter 4. Major Hazard Control

4.1 Superstar Technologies

4.7 Nuclear Hazard Control

4.8 Process Hazard Control: Background

4.9 Process Hazard Control: Advisory Committee on Major Hazards

4.10 Process Hazard Control: Major Hazards Arrangements

4.11 Process Hazard Control: Planning

4.12 Process Hazard Control: European Community

4.13 Process Hazard Control: USA

Chapter 5. Economics and Insurance

5.1 Economics of Loss Prevention

5.4 Level of Loss Prevention Expenditure

5.5 Insurance of Process Plant

5.8 Business Interruption Insurance

5.9 Other Insurance Aspects

Chapter 6. Management and Management Systems

6.2 Management Commitment and Leadership

6.3 Management Organization

6.5 Systems and Procedures

6.6 Project Safety Reviews

6.8 Standards and Codes of Practice

6.26 Safety Management Systems

6.27 Process Safety Management

6.28 CCPS Management Guidelines

Chapter 7. Reliability Engineering

7.1 Development of Reliability Engineering

7.2 Reliability Engineering in the Process Industries

7.3 Definition of Reliability

7.4 Meanings of Probability

7.5 Some Probability Relationships

7.6 Some Reliability Relationships

7.8 Reliability of Some Standard Systems

7.9 Reliability of Complex Systems

7.11 Joint Density Functions

7.12 Monte Carlo Simulation

7.17 Models of Failure: Strength–Load Interaction

7.18 Models of Failure: Some Other Models

7.19 Failure Behavior and Regimes

7.20 Failure Data Analysis

7.21 Reliability in Design

7.22 Reliability Prediction

7.23 Reliability Growth, Testing, and Demonstration

7.25 Maintenance Activities and Policies

7.26 Reliability-Centered Maintenance

Chapter 8. Hazard Identification

8.2 Management System Audits

8.9 Event Tree and Fault Tree Analysis

8.11 Preliminary Hazard Analysis

8.12 Screening Analysis Techniques

8.13 Hazard and Operability Studies

8.14 Failure Modes, Effects, and Criticality Analysis

8.20 Process Safety Review System

8.22 Filtering and Follow-up

8.23 Safety Review Systems

8.24 Hazard Ranking Methods

8.25 Hazard Warning Analysis

8.29 Quality Assurance: Completeness

8.30 Quality Assurance: QUASA

Chapter 9. Hazard Assessment

9.8 Cause–Consequence Diagrams

9.11 Rare Events and External Threats

9.12 Human Factors and Human Error

9.15 Population Characteristics

9.16 Modification of Exposure

9.18 Presentation of Results

9.19 Confidence in Results

9.23 Simplified Assessment Methods

9.27 Risk Assessment Debate

Chapter 10. Plant Siting and Layout

10.4 Layout Techniques and Aids

10.5 Layout Planning and Development

10.7 Plot Layout Considerations

10.11 Separation Distances

10.12 Hazardous Area Classification

10.18 Blast-Resistant Structures

Chapter 11. Process Design

11.2 Conceptual – Front End Design

11.5 Licensors, Vendors, and Contractors

11.6 Inherently Safer Design

11.8 Unit Operations and Equipments

11.11 Particular Chemicals

11.12 Particular Processes and Plants

11.13 Operational Deviations

11.15 CCPS Engineering Design Guidelines

11.16 Integration of Safety into the Process Design

Chapter 12. Pressure System Design

12.2 Pressure System Components

12.3 Steels and Their Properties

12.4 Pressure Vessel Design

12.5 Joining, Fastening, and Welding

12.6 Pressure Vessel Standards and Codes

12.9 Fired Heaters and Furnaces

12.12 Overpressure Protection

12.13 Overpressure Protection: Pressure Relief Devices

12.14 Overpressure Protection: Relief System Design

12.15 Overpressure Protection: Fire Relief

12.16 Overpressure Protection: Vacuum and Thermal Relief

12.17 Overpressure Protection: Special Situations

12.18 Overpressure Protection: Disposal

12.19 Overpressure Protection: Pressure Relief Valves

12.20 Overpressure Protection: Bursting Discs

12.21 Overpressure Protection: Installation of Relief Devices

12.22 Flare and Vent Systems

12.23 Blowdown and Depressuring Systems

12.24 Pressure Containment

12.25 Containment of Toxic Materials

12.26 Pressure Systems for Chlorine

12.27 Failure in Pressure Systems

12.29 Probabilistic Fracture Mechanics

12.30 Failure of Vessels, Equipment, and Machinery

12.31 Computer-Aid Pressure and Pressure Protection System Design

Chapter 13. Control System Design

13.1 Process Characteristics

13.2 Control System Characteristics

13.3 Instrument System Design

13.4 Process Computer Control

13.5 Control of Batch Processes

13.6 Control of Particular Units

13.7 Computer Integrated Manufacturing

13.11 Programmable Logic Systems

13.12 Programmable Electronic Systems

13.13 Software Engineering

13.14 Safety-Related Instrument Systems

13.15 CCPS Safe Automation Guidelines

13.16 Emergency Shut-Down Systems

13.18 Toxic Storage Instrumentation

Chapter 14. Human Factors and Human Error

14.1 Aims of Human Factors

14.2 Role of the Process Operator

14.3 Human Factors in Process Control

14.4 Process Operator Functions

14.5 Process Operator Studies

14.6 Allocation of Function

14.7 Human Information Processing

14.8 Case Studies in Human Error

14.9 Definition of Human Error

14.10 Human Factor Approaches to Assessing Human Error

14.11 Quantitative Human Reliability Analysis (HRA)

14.12 Success Likelihood Index Method (SLIM)

14.13 Human Error Assessment and Reduction Technique (HEART)

14.14 Dougherty and Fragola Method (D&F)

14.17 Human Factor Approaches to Mitigating Human Error

14.19 Human Error and Plant Design

14.20 Fault Administration

14.21 Malfunction Detection

14.26 CCPS Guidelines for Preventing Human Error in Process Safety

Chapter 15. Emission and Dispersion

15.3 Two-phase Flow: Fauske Models

15.4 Two-phase Flow: Leung Models

15.5 Vessel Depressurization

15.6 Pressure Relief Valves

15.16 Passive Dispersion: Models

15.17 Passive Dispersion: Dispersion over Particular Surfaces

15.18 Passive Dispersion: Dispersion in Particular Conditions

15.19 Passive Dispersion: Dispersion Parameters

15.20 Dispersion of Jets and Plumes

15.21 Dispersion of Two-phase Flashing Jets

15.22 Dense Gas Dispersion

15.23 Dispersion of Dense Gas: Source Terms

15.24 Dispersion of Dense Gas: Models and Modeling

15.25 Dispersion of Dense Gas: Modified Conventional Models

15.26 Dispersion of Dense Gas: Van Ulden Model

15.27 Dispersion of Dense Gas: British Gas/Cremer and Warner Model

15.28 Dispersion of Dense Gas: DENZ and CRUNCH

15.29 Dispersion of Dense Gas: SIGMET

15.30 Dispersion of Dense Gas: SLAB and FEM3

15.31 Dispersion of Dense Gas: HEGADAS and Related Models

15.32 Dispersion of Dense Gas: DEGADIS

15.33 Dispersion of Dense Gas: SLUMP and HEAVYGAS

15.34 Dispersion of Dense Gas: Workbook Model

15.35 Dispersion of Dense Gas: DRIFT and Related Models

15.36 Dispersion of Dense Gas: Some Other Models and Reviews

15.37 Dispersion of Dense Gas: Field Trials

15.38 Dispersion of Dense Gas: Thorney Island Trials

15.39 Dispersion of Dense Gas: Physical Modeling

15.40 Dispersion of Dense Gas: Terrain, Obstructions, and Buildings

15.41 Dispersion of Dense Gas: Validation and Comparison

15.42 Dispersion of Dense Gas: Particular Gases

15.43 Dispersion of Dense Gas: Plumes from Elevated Sources

15.44 Dispersion of Dense Gas: Plumes from Elevated Sources – PLUME

15.45 Concentration and Concentration Fluctuations

15.46 Flammable Gas Clouds

15.48 Dispersion over Short Distances

15.49 Hazard Ranges for Dispersion

15.50 Transformation and Removal Processes

15.51 Infiltration into Buildings

15.52 Source and Dispersion Modeling: CCPS Guidelines

15.53 Vapor Release Mitigation: Containment and Barriers

15.54 Vapor Cloud Mitigation: CCPS Guidelines

15.57 Classification of Models

16.2 Flammability of Gases and Vapors

16.4 Flammability of Aerosols

16.9 Hazardous Area Classification

16.11 Fire in Process Plant

16.13 Radiant Heat Transfer

16.16 Fireballs from Explosives

16.21 Effects of Fire: Damage

16.22 Effects of Fire: Injury

16.23 Fire Protection of Process Plant

16.24 Passive Fire Protection

16.25 Fire Fighting Agents

16.26 Fire Protection Using Water: Extinguishment and Control

16.27 Fire Protection Using Water: Exposure Protection

16.28 Fire Protection Using Foam

16.29 Fire Protection Using Dry Chemicals

16.30 Fire Protection Using Vaporizing Liquids

16.31 Fire Protection Using Inert Gas

16.32 Fire Protection Using Special Methods

16.33 Fire Protection Using Portable Extinguishers

16.34 Fire Protection Applications

16.35 Firefighting in Process Plant

16.36 Fire and Fire Protection in Buildings

16.37 Fire Protection in Transport

16.39 Hazard Range of Fire

17.5 Deflagration Inside Plant

17.6 Detonation Inside Vessels and Pipes

17.7 Explosions in Closed Vessels

17.8 Explosions in Buildings

17.9 Explosions in Large Enclosures

17.10 Explosion Prevention

17.11 Explosion Protection

17.12 Explosion Venting of Vessels

17.13 Explosion Venting of Ducts and Pipes

17.14 Explosion Relief of Buildings

17.15 Explosion Relief of Large Enclosures

17.17 Venting of Reactors and Vessels: DIERS

17.18 Venting of Reactors and Vessels: Vent Flow

17.19 Venting of Reactors and Vessels: Vent Sizing

17.20 Venting of Reactors and Vessels: Leung Model

17.21 Venting of Reactors and Vessels: ICI Scheme

17.22 Venting of Reactors: Relief Disposal

17.23 Venting of Reactors: CCPS Work

17.24 Venting of Storage Vessels

17.25 Explosive Shock in Air

17.26 Condensed Phase Explosions

17.27 Vessel Burst Explosions

17.28 Vapor Cloud Explosions

17.29 Boiling Liquid Expanding Vapor Explosions

17.30 Explosions in Process Plant

17.31 Effects of Explosions

17.32 Explosion Damage to Structures

17.33 Explosion Damage to Housing

17.34 Explosion Damage by Missiles

17.35 Explosion Damage to Plant by Missiles

17.36 Explosion of a Cased Explosive

17.37 Explosion of an Explosive Load

17.38 Explosion Injury to Persons Outdoors

17.39 Explosion Injury to Persons Indoors

17.40 Explosion Injury from Flying Glass

17.41 Explosion Injury from Penetrating Fragments

17.42 Explosion Injury from Penetrating Fragments: Model of Gilbert, Lees, and Scilly

17.44 Dust Explosibility Characteristics

17.45 Dust Ignition Sources

17.46 Dust Explosion Prevention

17.47 Dust Explosion Protection

17.48 Dust Explosion Venting

17.52 Hazard Range of Explosions

18.4 Control of Toxic Hazard: Regulatory Controls

18.6 Hygiene Standards: Occupational Exposure Limits

18.10 Emergency Exposure Limits

18.12 Gas Toxicity: Experimental Determination

18.13 Gas Toxicity: Physiological Factors

18.14 Gas Toxicity: Toxicity Data

18.15 Gas Toxicity: Vulnerability Model

18.16 Gas Toxicity: Major Industrial Gases

18.17 Gas Toxicity: MHAP Studies

18.18 Gas Toxicity: Chlorine

18.19 Gas Toxicity: Green Book Relations

18.20 Gas Toxicity: Probit Equations

18.21 Gas Toxicity: HSE Dangerous Dose

18.22 Gas Toxicity: Combustion Gases

18.23 Ultratoxic Substances

18.24 Plant Design for Toxic Substances

18.26 Toxic Release Response

18.27 Toxic Release Case Histories

18.29 Chlorine Hazard Assessment

18.30 Other Chemicals Hazard Assessment

18.31 Hazard Assessment Methodology

Chapter 19. Plant Commissioning and Inspection

19.3 Pressure Vessel Inspection

19.4 Pressure Piping Systems Inspection

19.5 Non-Destructive Testing

19.6 Materials Verification

19.8 Leak Testing and Detection

19.10 Performance Monitoring

19.11 Condition Monitoring

19.12 Vibration Monitoring

19.13 Corrosion Monitoring

19.14 Acoustic Emission Monitoring

19.15 Plant Monitoring: Specific Equipment

19.16 Pipeline Inspection and Monitoring

Chapter 20. Plant Operation

20.1 Inherently Safer Design to Prevent or Minimize Operator Errors

20.3 Good Operating Practices

20.4 Operating Procedures and Instructions

20.6 Handover and Permit Systems

20.9 Modifications to the Process

20.10 Operation and Maintenance

20.11 Start-up and Shut-Down

20.12 Start-up of Refinery Units

20.13 Shut-down of Refinery Units

20.14 Operation of Fired Heaters

20.16 Operation of Storage

20.17 Operational Activities and Hazards

20.20 Identification Measures

20.21 Exposure of Personnel

Chapter 21. Equipment Maintenance and Modification

21.1 Management of Maintenance

21.2 Hazards of Maintenance

21.3 Preparation for Maintenance

21.9 Maintenance Equipment

21.12 Tank Cleaning, Repair and Demolition

21.14 Maintenance of Particular Equipment

21.16 Deteriorated Equipment

21.17 Some Maintenance Problems

21.19 Maintenance Information Systems

21.22 Modifications to Equipment

21.23 Software and Network Maintenance

21.25 Some Modification Problems

21.26 Major Plant Expansions

21.27 Maintenance Optimization

21.28 Maintenance Personnel Training

22.1 General Considerations

22.3 Petroleum Product Storage

22.4 Storage Tanks and Vessels

22.5 Selection of Materials for Storage Tanks

22.8 Fire Prevention and Protection

22.10 LPG Storage: Pressure Storage

22.11 LPG Storage: Refrigerated Storage

22.13 LNG Storage: Refrigerated Storage

22.16 High Toxic Hazard Materials: CCPS Guidelines

22.19 Ammonia Storage: Pressure Storage

22.20 Ammonia Storage: Refrigerated Storage

22.21 Ammonia Storage: Stress Corrosion Cracking

22.22 Other Chemicals Storage

22.24 Underground Storage Tanks

22.25 Glass Reinforced Plastic Storage

22.27 Loading and Unloading Facilities

22.28 Loading and Unloading Facilities: Particular Chemicals

22.29 Drum and Cylinder Storage

22.31 Warehouses: Particular Chemicals Storage

22.32 Storage Case Histories

22.34 LPG Storage Hazard Assessment

22.35 LNG Storage Hazard Assessment

22.36 Ammonia Storage Hazard Assessment

22.37 Storage Tanks Protection from Terrorism

23.1 General Considerations

23.3 Classification, Packaging, and Labeling

23.6 Road Transport Environment

23.8 Rail Transport Environment

23.9 Road and Rail Tunnels

23.12 Marine Transport: Shipping

23.13 Marine Transport: Regulatory Controls

23.14 Marine Transport: Ports and Harbors

23.15 Marine Transport: Shipboard Fire and Fire Protection

23.16 Marine Transport: Liquefied Flammable Gas

23.17 Marine Transport: Chemicals

23.18 Marine Transport Environment

23.20 Transport Emergency Planning and Spill Control

23.21 Transport Case Histories

23.23 Transport Risk Assessment

23.24 Road Transport Risk Assessment

23.25 Rail Transport Risk Assessment

23.26 Tunnel Transport Risk Assessment

23.27 Pipeline Transport Risk Assessment

23.28 Marine Transport Risk Assessment

23.29 Transport Hazard Assessment: Comparative Risks

Chapter 24. Emergency Planning

24.2 On-site Emergency Planning

24.3 Resources and Capabilities

24.4 Developing an Emergency Plan

24.6 Essential Functions and Nominated Personnel

24.7 Declaration and Communication of the Emergency

24.9 Cooperation and Drills

24.11 Off-Site Emergency Planning

24.12 Transport Emergency Planning

24.13 Emergency Planning for Disasters

24.17 Regulations and Standards

Appendix A NFPA Publications

Chapter 25. Personal Safety

25.4 COSHH Regulations 1988

25.9 Physico-Chemical Hazards

25.10 Ionizing Radiation Hazards

25.11 Non-Ionizing Radiation Hazards

25.14 Other Activities and Hazards

25.15 Personal Protective Equipment

25.16 Respiratory Protective Equipment

25.17 Rescue and First Aid

Chapter 26. Accident Research

26.1 Definition of Accidents

26.2 Classification of Accidents

26.8 Impact of Safety Culture

26.10 Major Hazards Research

Chapter 27. Information Feedback

27.5 Accident Investigation

27.7 Explosion Investigation

27.8 Accident Investigation: CCPS Guidelines

27.9 Public Accident Inquiries

27.10 Organizational Memory

27.12 Information Exchange

27.14 Safety Performance Measurement

27.15 Safety Performance Monitoring

Chapter 28. Safety Management Systems

28.3 Safety Policy Statement

28.4 Safety Representatives

28.11 Management Procedure to Implement Required Changes to Establish Proper Safety

28.12 Use of Tools for Better Safety Management Systems

29.1 Expert Systems in Process Engineering

29.2 Combination of Process Safety with Design and Optimization

29.3 Computer Aided Process Engineering

29.4 Pipework and Fluid Flow

29.5 Unit Operation and Equipment

29.6 Databases, Bibliographies, and Indexes

29.7 Compliance Management

29.8 Computational Fluid Dynamics

29.9 Hazard Identification

29.10 Pressure Relief Devices Sizing

29.11 Hazard Assessment Systems

Chapter 30. Artificial Intelligence and Expert Systems

30.1 Knowledge Representation

30.5 Non-Deductive Inference

30.8 Uncertainty and Inconsistency

30.9 Probabilistic Reasoning

30.11 Programming Languages

30.12 Structured Knowledge

30.14 Matching and Pattern Recognition

30.15 Problem-Solving and Games

30.22 Graphs, Trees, and Networks

30.25 Expert Systems: Some Systems and Tools

30.26 Qualitative Modeling

30.28 Process Applications

30.33 Plant Design: Synthesis

30.34 Plant Design: Analysis

30.35 Expert Systems: Some Process Systems

30.37 Hazard Identification

30.38 Hazard Identification: HAZID

30.39 Hazard Identification: Enhancements

30.41 Fault Tree Synthesis

30.42 Fault Tree Synthesis: FAULTFINDER

30.43 Operating Procedure Synthesis

30.45 Fault Administration

30.46 Malfunction Detection

Chapter 31. Incident Investigation

31.2 General Investigation Concepts

31.4 The Investigation Team

31.5 Identifying Root Causes

31.6 Recommendations, Reports, and Lessons Learned

31.7 Management System for Investigations

Chapter 32. Inherently Safer Design

32.3 History of Inherently Safer Design

32.4 Strategies for Process Risk Management

32.5 Inherently Safer Design Strategies

32.6 Inherently Safer Design Conflicts

32.7 Measuring Inherent Safety Characteristics of a Process

32.8 Inherently Safer Design and the Process Life Cycle

32.9 Implementing Inherently Safer Design

32.10 Inherent Safety and Chemical Plant Security

32.11 Inherently Safer Design References

Chapter 33. Reactive Chemicals

Chapter 34. Safety Instrumented Systems

34.4 Layers of Protection Analysis (LOPA)

34.11 Special Applications

Chapter 35. Chemical Security

35.2 Security Management System

35.4 Countermeasures and Security Risk Management Concepts

35.6 Defining the Risk to be Managed

35.7 Overview of an SVA Methodology

35.8 Chemical Facility Anti-Terrorism Standards (CFATS)

35.9 Chemical Security Assessment Tool (CSAT)

35.10 Inherently Safer Technology (IST)

Chapter 36. Safety Culture

36.2 Definition of Safety Culture

36.3 Developments in Safety Culture

36.4 Evaluating Safety Culture

36.5 Implementing Safety Culture

Chapter 37. Metrics and Performance Measurements

37.2 Different Types of Metrics

37.3 Choosing Useful Metrics

37.4 Implementing the Selected Metrics

37.5 Application of Metrics with Examples

37.6 Future Efforts for Generating Industry-Wide Metrics

Chapter 38. Benchmarking in the Process Industry

38.3 Possible Barriers and Resolutions for Benchmarking

38.4 Examples of Benchmarking Activities

Chapter 39. Liquefied Natural Gas

39.4 LNG Spills Experiments and Modeling

39.5 Safety Measures in LNG Facilities

39.6 Regulatory Authorities and Regulations

Chapter 40. Sustainable Development

40.1 Sustainable Development Concepts

40.2 Sustainable Development Principles for Engineering

40.3 Sustainability Measurement

Appendix 1: Case Histories

A1.3 Reporting of Incidents

A1.4 Reporting of Injuries in Incidents

A1.5 Reporting of Injuries at National Level

A1.6 Incident Diagrams, Plans, and Maps

A1.7 Incidents Involving Fire Fighting

A1.8 Incidents Involving Condensed Phase Explosives

A1.9 Incidents Involving Spontaneously Combustible Substances

A1.10 Case Histories: Some Principal Incidents

A1.11 Case Histories: A Series

A1.12 Case Histories: B Series

A1.13 Some Other Incidents and Problems

A2.1 The Company and the Management

A2.2 The Site and the Works

A2.3 The Process and the Plant

A2.4 Events Prior to the Explosion

A2.8 Some Lessons of Flixborough

A2.10 Recent CFD Reports About Flixborough

A3.1 The Company and the Management

A3.2 The Site and the Works

A3.3 The Process and the Plant

A3.4 TCDD and its Properties

A3.5 Previous Incidents Involving TCP and TCDD

A3.6 Events Prior to the Release

A3.8 The Emergency and the Immediate Aftermath

A3.11 The Later Aftermath, Contamination, and Decontamination

A3.12 Some Lessons from Seveso

A4.1 The Site and the Plant

A4.2 The Fire and Explosion – 1

A4.4 The Fire and Explosion − 2

A4.5 Some Lessons of Mexico City

A5.1 The Company and the Management

A5.2 The Site and the Works

A5.3 The Process and the Plant

A5.4 MIC and its Properties

A5.5 Events Prior to the Release

A5.7 The Emergency and the Immediate Aftermath

A5.10 Some Lessons of Bhopal

A6.1 The Site and the Plant

A6.2 Events Prior to the Explosion

A6.4 The Emergency and the Aftermath

A6.5 Some Lessons of Pasadena

Appendix 7: Canvey Reports

A7.2 First Canvey Report: Installations and Activities

A7.3 First Canvey Report: Identified Hazards

A7.4 First Canvey Report: Failure and Event Data

A7.5 First Canvey Report: Hazard Models and Risk Estimates

A7.6 First Canvey Report: Assessed Risks and Actions

A7.7 First Canvey Report: Responses to Report

A7.9 Second Canvey Report: Reassessed Risks and Actions

A7.10 Second Canvey Report: Technical Aspects

Appendix 8: Rijnmond Report

A8.2 Installations and Activities

A8.6 Population Characteristics

A8.7 Mitigation of Exposure

A8.8 Individual Assessments

A9.2 Laboratory Management Systems

A9.9 Laboratory Storage and Waste Disposal

A9.10 Laboratory Operation

A9.11 Laboratory Fire and Explosion Protection

A10.1 Pilot Plant Uses, Types, and Strategies

A10.2 Pilot Plant Features and Hazards

A10.5 Pilot Plant Operation

A10.7 Pilot Plant Programs

A10.8 Cost Estimating for Pilot Plants

Appendix 11: Safety, Health, and the Environment

Safety, Health, and the Environment

Pollution of the Environment

A12.3 Noise Control Terminology

Appendix 13: Safety Factors for Simple Relief Systems

A13.1 Comments on Safety Factors to be Applied When Sizing a Simple Relief System

Appendix 14: Failure and Event Data

A14.2 Definition and Regimes of Failure

A14.11 Inventory of Equipment in Plants

A14.20 Fire and Gas Detection Systems

A14.21 Fire Protection Systems

A14.22 Emergency Shut-Down Systems

A14.27 Explosion Following Ignition

A15.1 Earthquake Geophysics

A15.2 Earthquake Characterization

A15.4 Earthquake Incidents

A15.6 Ground Motion Characterization

A15.7 Ground, Soils, and Foundations

A15.8 Earthquake-resistant Design

A15.9 Earthquake Design Codes

A15.10 Dynamic Analysis of Structures

A15.11 Seismicity Assessment and Earthquake Prediction

A15.12 Design Basis Earthquake

A15.13 Nuclear Installations

A15.14 Process Installations

Appendix 16: San Carlos De La Rapita Disaster

A16.3 The Fire and Explosions – 1

A16.4 The Emergency and the Aftermath

A16.5 The Fire and Explosions – 2

A16.6 Judgment of the Court

A16.7 Lessons of San Carlos De La Rapita Disaster

Appendix 17: ACDS Transport Hazards Report

A17.2 Substances and Activities

A17.6 Population Characteristics

A17.9 Marine Transport: Ports

A17.10 Transport of Explosives

A17.13 Risk Evaluation and Remedial Measures

Appendix 18: Offshore Process Safety

A18.1 North Sea Offshore Regulatory Administration

A18.2 Gulf of Mexico Offshore Regulatory Administration

A18.3 Offshore Process Safety Management

A18.5 Inherently Safer Design

A18.6 Offshore Emergency Planning

A19.1 The Company, the Management, and the Personnel

A19.2 The Field and the Platform

A19.3 The Process and the Plant

A19.4 Events Prior to the Explosion

A19.5 The Explosion, the Escalation, and the Rescue

A19.7 Some Lessons of Piper Alpha

A19.8 Recommendations on the Offshore Safety Regime

Appendix 20: Nuclear Energy

A20.4 Nuclear Waste Treatment

A20.5 Nuclear System Reliability

A20.6 Nuclear Hazard Assessment

A20.7 Nuclear Pressure Systems

A20.8 Nuclear Reactor Operation

A20.9 Nuclear Emergency Planning

A20.10 Nuclear Incident Reporting

Appendix 21: Three Mile Island

A21.1 The Company and the Management

A21.2 The Site and the Works

A21.3 The Process and the Plant

A21.4 Events Prior to the Excursion

A21.6 The Emergency and the Aftermath

A21.9 Some Lessons of Three Mile Island

A22.1 The Operating Organization and the Management

A22.2 The Site and the Works

A22.3 The Process and the Plant

A22.4 Events Prior to the Release

A22.6 The Emergency and the Immediate Aftermath

A22.10 Some Lessons of Chernobyl

Appendix 23: Rasmussen Report

A23.2 Risk Assessment Methodology

A23.11 Population Characteristics

A23.12 Mitigation of Exposure

A23.14 Uncertainty in Results

A23.15 Presentation of Results

A23.16 Evaluation of Results

A23.17 Browns Ferry Incident

A23.18 Critical Assumptions

Appendix 24: ACMH Model License Conditions

A24.1 Model Conditions for a Possible Licensing Scheme for Selected High Hazard Notifiable Installations

Appendix 25: HSE and HSL Guidelines

A25.1 The Siting of Developments in the Vicinities of Major Hazards: HSE’s Draft Guidelines to Planning Authorities (by the Health and Safety Executive – Major Hazards Assessment Unit)

A25.2 HSE Guidelines on LNG Facility

A25.3 HSE Guidelines on Chemical Industries

A25.4 HSL Guidelines on Explosion Modeling and Deficiencies

Appendix 26: Public Planning Inquiries

Appendix 27: Standards and Codes

A27.1 Globalization of Standards

A27.2 Where to Find Information on Standards

Appendix 28: Institutional Publications

Appendix 29: Information Sources

A29.1 Selected Organizations Relevant to Safety and Loss Prevention

Appendix 30: Units and Unit Conversions

A30.1 Absolute and Gauge Pressures

A30.2 Other Units and Conversions

Appendix 31: Process Safety Management (PSM) Regulation in the United States

A31.1 The Process Safety Management Program

A31.2 Summary Comparison of OSHA Elements with CCPS Elements

A31.3 National Emphasis Program

Appendix 32: Risk Management Program Regulation in the United States

A32.1 The Risk Management Program

Appendix 33: Incident Databases

A33.2 Injury and Fatality Databases (Not Tied to Specific Incidents)

A33.3 Incident Investigation Reports

A34.2 Technical Information

A34.3 University Academic Programs

A34.4 Government Organizations

A34.5 Societies, Councils, Institutes

A34.6 Security and Vulnerability Assessment

Appendix 35: Hurricanes Katrina and Rita

A35.4 Effect on the Industry

Appendix 36: BP America Refinery Explosion, Texas City, Texas, USA

A36.2 Overview of BP Management Framework and Organizational Structure

A36.3 Incident Description

A36.4 Root and Contributing Causes

Appendix 37: Buncefield Incident

A37.1 Description of the Incident

A37.2 Causes of the Incident

A37.3 Lessons Learned from the Incident

A37.4 Regulations and Standards in the Industry after the Incident

Appendix 38: Space Shuttle Columbia Disaster

A38.1 Development of the Space Shuttle Program

A38.2 Columbia’s Final Flight

A38.4 Other Factors Considered

A38.5 From Challenger to Columbia

A38.6 Decision Making at NASA

A38.7 The Accident’s Organizational Causes

A38.8 History as Cause: Columbia and Challenger

A38.9 Implications for the Future of Human Space Flight

A38.10 Other Significant Observations

Appendix 39: Tank Farm Incidents

A39.2 Hazards in Tank Farms

A39.3 Prevention of Tank Farm Incidents

A39.4 Related Regulations about Tanks and Tank Farms

A39.7 Case Study Material and Examples

A39.8 Tank Farm Spacing Study: Optimization Model

A39.9 Optimization Model Formulations

A39.10 Modeling Case Study

Appendix 40: Deepwater Horizon

A40.1 Lessons from the Deepwater Horizon Incident

A40.2 The Companies and the Management

A40.3 The Site and the Works

A40.4 Deepwater Horizon and Drilling Operations

A40.5 Events Prior to the Explosions

A40.6 The Emergency and Evacuation

Appendix 41: Safety Characteristics Database CHEMSAFE®

A41.2 The Database CHEMSAFE®

A41.4 Classifying Hazardous Substances and Dangerous Goods Using CHEMSAFE®


Rock Fractures and Fluid Flow: Contemporary Understanding and Applications (1996)

The heterogeneity and complexity of flow paths in fractured rocks make field studies very difficult. As a result, there are relatively few field study sites where the distribution and character of fractured rocks have been described in detail. These sites are an extremely valuable scientific resource for a number of reasons. First, field testing and verification of various fracture characterization methods and data analysis techniques require sites where these methods can be developed, applied, and evaluated. Case history studies from such well-documented field sites are useful for demonstrating the application of specific techniques. These studies illustrate how different fracture characterization techniques can be applied to radioactive waste repository siting or water resource development, for example. The careful and thorough documentation of fractures, geomechanical properties of fractured rocks at various scales, and the patterns of tracer dispersal through fractures provide insights into how large-scale geological structure and tectonic history relate to the details of fracture properties and fracture distribution as identified in boreholes, core samples, and outcrops.

A list of some of the better-documented sites where fractured rocks have been studied is provided in Table 8.1. The table lists the locations of the sites, the rock types involved, the depths of investigation, and the primary applications for which the studies were intended. The table does not describe all sites in existence but does provide a representative sample of sites where work has been carried out, and it gives a reasonably complete series of examples of the various fracture characterization techniques that can be applied in the field. The application supporting the majority of the long-term, large-scale fracture studies is high-level radioactive waste repository siting in North American and Europe. Most of

TABLE 8.1 Summary of Fracture Study Sites

Underground Research Laboratory

Southeast Manitoba, Canada

Radioactive waste disposal

Martin (1990) Everitt et al. (1990) Paillet (1991)

White Mountains, New Hampshire

Shapiro and Hsieh (1994) Paillet and Kapucu (1989) Morganwalp and Aronson (1994)

Columbia River Plateau, Central Washington

Radioactive waste disposal

Kim and McCabe (1984) Paillet and Kim (1987)

Santa Catalina Mountains, South-Central Arizona

Radioactive waste disposal

Radioactive waste disposal

Olsson (1992) Nelson et al. (1982)

Crystalline Alps, Switzerland

Radioactive waste disposal

Argonne, Northeast Illinois

Robinson et al. (1993) Nicholas and Healy (1988) Silliman and Robinson (1989)

Robinson and Tester (1984) Fehler (1989) Block et al. (1994)

Natural gas resources development

Natural gas resources development

Lorenz and Finley (1991) Lorenz et al. (1989)

Radioactive waste disposal

Geothermal Resources Council (1992) Oppenheimer (1986)

Radioactive waste disposal

Andersson et al. (1991) Gustaffson and Andersson (1991)

South-Central Ontario, Canada

Radioactive waste disposal

Paillet and Hess (1986) Kamineni et al. (1987) Ticknor et al. (1989)

Radioactive waste disposal

Paillet and Hess (1987) Stone and Kamineni (1982) Kamineni and Bonardi (1983)

Bredehoeft et al. (1983) Neuzil (1993)

Laubach (1988) Laubach et al. (1988)

Waste Isolation Pilot Project

Radioactive waste disposal

Davies et al. (1991) Beauheim (1988)

Radioactive waste disposal

Radioactive waste disposal

Northwestern Coast of England

Radioactive waste disposal

these studies deal with crystalline rocks. The sites listed in Table 8.1 are too numerous to be described in detail in this report. Each entry is associated with one or two key references to provide the most efficient introduction to the literature. A few representative sites are discussed in detail in the following sections.

CASE HISTORY I. U.S. GEOLOGICAL SURVEY FRACTURED ROCK RESEARCH SITE NEAR MIRROR LAKE, NEW HAMPSHIRE

The U.S. Geological Survey is conducting research on fluid flow and solute transport in fractured rock at a site near Mirror Lake in central New Hampshire (Winter, 1984 Shapiro and Hsieh, 1991). Started in 1990, this study aims to (1) develop and assess field methods for characterizing fluid flow and solute transport in fractured rocks (2) develop a multidisciplinary approach that uses geological, geophysical, geochemical, and hydrological information for data interpretation and model building and (3) establish a site for long-term monitoring. The discussion below summarizes the preliminary results of this ongoing study. Additional information can be found in an overview paper by Shapiro and Hsieh (1995) and in a series of papers edited by Morganwalp and Aronson (1995).

Mirror Lake lies at the lower end of the Hubbard Brook valley in the southern White Mountains of New Hampshire. The surface area that drains into Mirror Lake occupies 0.85 km 2 of mountainous terrain, which varies in altitude from 213 m at the lakes surface to 481 m at the top of the drainage divide. The bedrock is a sillimanite-grade schist extensively intruded by granite, pegmatite, and lesser amounts of lamprophyre. It is covered by 0 to 55 m of glacial drift. Outcrops are few the largest exposure of bedrock occurs where a highway cuts through a small hill. Here, four subvertical surfaces, exposed by road construction, and one subhorizontal surface, cleared by glaciation, provide approximately 8,000 m 2 of exposed rock for mapping and studying fractures and geology. The roadcut shows a complex distribution of rock types. The schist is multiply folded. The granitic intrusions occur as dikes, irregular pods, and anastomosing fingers, ranging in width from centimeters to meters. Pegmatite and basalt dikes cross-cut both the schist and granite.

Investigations at the Mirror Lake site are proceeding at two scales: the 100-m scale and the kilometer scale. The 100-m-scale investigations focus on several subregions, each occupying an area of approximately 100 × 100 m. The goal is to characterize in detail the fracture geometry and the hydraulic and transport properties to a depth of about 80 m. The kilometer-scale investigations cover approximately 1 km 2 (Figure 8.1), including the entire surface area that drains into Mirror Lake. The site investigations are proceeding outward from the vicinity of the lake in a systematic fashion, and some of the most recently drilled bedrock boreholes are located in areas beyond the actual surface watershed. The goal is to characterize the large-scale movement of groundwater to a depth of about 250 m.

FIGURE 8.1 The Mirror Lake, New Hampshire, study area, showing the location of individual bedrock well and the two well fields. The larger of the two squares represents the FSE borehole array, and the smaller represents the CO array. From Paillet and Kapucu (1989).

100-m-Scale Investigation

The 100-m-scale investigations use many of the tools described in Chapter 2 (fracture mapping), Chapter 4 (fracture detection by geophysical methods), and Chapter 5 (hydraulic and tracer tests). Surficial mapping of fractures is carried out at the highway roadcut. For subsurface investigations, two well fields (Forest Service East, or FSE, and Camp Osceloa, or CO) have been established (Figure 8.1). In the following discussion of characterization techniques used at the Mirror Lake site, the reader can find a detailed description of the fracture mapping, geophysical method, and hydraulic tracer test methods in Chapters 2, 4, and 5.

At the highway roadcut, fractures were mapped by the ''pavement method" developed by Barton and Larson (1985) and described by Barton and Hsieh (1989). This method consists of (1) making a detailed map of the fractures on an exposed rock surface (pavement) (2) measuring the orientation, surface roughness, aperture, mineralization, and trace length of each fracture and

(3) measuring the connectivity, density, and scaling characteristics of the fracture network. Results suggest a correlation between fracturing and rock type. The granite is more densely fractured with shorter and more planar fractures. The schist has fewer and less planar fractures. Connectivity of the fracture network at Mirror Lake is low compared to fractures mapped in volcanic tuff, quartz diorite, limestone, and sandstone at other sites. The low connectivity at the Mirror Lake site suggests that fluid moves through highly tortuous paths in the bedrock.

In a 100 × 100 m area adjacent to the CO well field, directional soundings using direct current electricity and refracted seismic waves were carried out to determine the predominant strikes of near-vertical fractures in the bedrock, which underlies 3 to 10 m of glacial drift. Analyses yield predominant strikes of N 30° E from the electrical sounding and N 22° E from the seismic survey. These orientations agree closely with the predominant strike of 30° determined from fractures mapped at the highway roadcut. The agreement suggests that, where overburden is thin (e.g., less than 10 m), directional sounding can be an effective method for determining the predominant strikes of near-vertical fractures.

At the FSE well field west of Mirror Lake, 13 wells were drilled in a 120 × 80 m area (Figure 8.2). Drill cuttings and downhole video camera images show that the wells penetrate varying thicknesses of schist, granite, and pegmatite but that there is little to no apparent correlation in the distribution of rock types in neighboring wells. Borehole televiewer logs show that, between depths of 20 m (bedrock surface) and 80 m, each well intersects 20 to 60 fractures. With a few exceptions, these fractures do not project from one well to another (Hardin et al., 1987 Paillet, 1993). In each well, water-producing fractures were determined by single-borehole flowmeter surveys and single-borehole packer tests. The results show that one to three fractures in each well together produce more than 90 percent of the water when the well is pumped. The remaining fractures are less transmissive by two to five orders of magnitude. These findings suggest that bedrock underlying the FSE well field contains a small number of highly transmissive fractures within a larger network of less transmissive fractures.

The geometry and interconnectivity of the highly transmissive fractures were examined by cross-hole flowmeter survey (pumping one well and measuring vertical velocity in an observation well), vertical seismic profiling, seismic and electromagnetic tomography, multiple-borehole hydraulic tests, and converging-flow tracer tests. These field data are still under analysis, but a conceptual picture of the fracture network is emerging. The highly transmissive fractures appear to form local clusters each fracture cluster occupies a near-horizontal, tabular-shaped volume several meters thick and extends laterally a distance of 10 to 40 meters. These clusters are connected to each other via a network of less transmissive fractures. Figure 8.3 illustrates the inferred locations of four highly transmissive fracture clusters, marked A through D, in the vertical section between wells FSE1 and FSE6.

FIGURE 8.2 Locations of the 13 boreholes in the Forest Service East (FSE) well field at the Mirror Lake site. See Figure 8.1 for location of the FSE well field in the Mirror Lake area. From Hsieh and Shapiro (1994).

Preliminary analyses of the geophysical tomography results suggest that these techniques are extremely valuable for tracing the high-transmissivity zones between wells. For example, in the vertical section between wells FSE1 and FSE4 (14 m apart), fracture cluster B was detected by seismic and electromagnetic tomography and also by vertical seismic profiling. The low-velocity region in the electromagnetic tomogram (Figure 8.4) agrees closely with the highly transmissive fractures identified by flowmeter survey and hydraulic testing. At greater separation distances between wells, however, the tomogram becomes more fuzzy, owing to decreasing signal strength at the receivers. There are also instances in which a low-velocity zone in a tomogram does not correlate with a high-transmissivity fracture zone, possibly because of heterogeneities in rock properties. Therefore, hydraulic tests are needed to interpret the tomography results. Difference tomography (comparing tomographs made before and after injecting

FIGURE 8.3 Vertical cross section between wells FSE1 and FSE6 at the Forest Service East well field. Four clusters of highly permeable fractures labeled A, B, C, and D occur in the less permeable fractured rocks. Borehole packers are shown in black. Modified from Shapiro and Hsieh (1994).

electrically conductive fluid into a fracture zone Andersson et al., 1989) could also help in resolving ambiguities.

The highly transmissive fracture clusters in the FSE well field exert a strong influence on multiple-borehole hydraulic tests. To prevent hydraulic communication through the wells, fracture clusters in each well are isolated from one another by packers, as illustrated by Figure 8.3. During pumping, the drawdown behavior is different from that in a homogeneous aquifer. If two packer-isolated intervals straddle the same fracture cluster, the drawdowns in the two intervals tend to be nearly identical. In contrast, if two packer-isolated intervals straddle different fracture clusters, the drawdowns are significantly different.

To analyze these tests, analytical methods are generally not suitable because they are based on oversimplified assumptions. Instead, a conventional porousmedium type numerical model is used to simulate the highly transmissive fracture clusters as high-permeability zones and the surrounding network of less transmissive fractures as low-permeability zones. Preliminary analyses yield transmissivities in the range of 10 -5 to 10 -4 m 2 /s for the highly transmissive fracture clusters, and an equivalent hydraulic conductivity of about 10 -7 m/s for the surrounding rock mass.

FIGURE 8.4 Electromagnetic velocity tomogram in vertical section between wells FSE1 and FSE4. From Hsieh et al. (1993).

Kilometer-Scale Investigations

Compared to the 100-m scale investigation, kilometer-scale investigations are less detailed for practical reasons. Drilling a dense network of wells (e.g., on a square grid of 50-m spacing) throughout the entire 1-km 2 study area is too expensive. In fact, such a dense network of wells might be undesirable. If left open, the wells could alter the natural flow of groundwater by connecting previously unconnected fractures. Another constraint on the kilometer-scale investigation is that many of the tools described in Chapters 4 and 5 provide information on small volumes of rock. Fracture detection methods (such as borehole logging and cross-hole tomography) are typically limited to less than 100 m of penetration. Hydraulic and tracer tests also are impractical. Response to pumping becomes undetectable beyond a few hundred meters from the pumping well, and tracer movement over a kilometer may take many years. Therefore, kilometer-scale investigations aim to characterize the large-scale flow of groundwater while neglecting small-scale details.

The kilometer-scale investigation monitors the response of the groundwater system to natural perturbations and long-term human disturbances. For example,

seasonal and long-term variations in infiltration to the groundwater system cause fluctuations in hydraulic heads. By monitoring the recharge and discharge of groundwater and the temporal and spatial variations in hydraulic head, it may be possible to infer hydraulic properties on the kilometer scale. Collection of groundwater samples for chemical analysis is another method for kilometer-scale investigations. Recent advances in the detection of human-made chemicals such as chlorofluorocarbons (used as refrigerants and aerosol propellants) and the parent-daughter isotopes tritium and helium-3 (produced from atmospheric testing of thermonuclear devices) have made it possible to determine the ages of shallow groundwaters (Busenberg and Plummer, 1992 Solomon et al., 1992). Knowledge of the spatial distribution of groundwater ages can help identify flow paths. As groundwater flows from recharge to discharge areas, its chemical composition evolves as the water reacts with the rock. Understanding this chemical evolution can help determine groundwater velocity.

Hydrological monitoring in the study area includes precipitation measurements at two locations, streamflow and lake discharge measurements using flumes, various meteorological measurements for evaporation calculations, and the construction of 14 well sites for hydraulic head monitoring and groundwater sampling. Each site consists of a well drilled into bedrock with packers and piezometers installed at different depths. Multiple packers are installed in the bedrock portions of the wells to allow hydraulic head measurements at different depths. The packers also prevent hydraulic communication between fractures through the wellbore. Over 30 piezometers, screened at the water table, are installed throughout the study area to monitor the position of the water table in the glacial drift.

Hydrological properties on the kilometer scale are inferred from modeling studies. As a base case, the bedrock and glacial drift are each represented as a layer of porous medium. Each layer has a homogeneous and isotropic hydraulic conductivity. Calibration of this model to match observed hydraulic heads and stream discharges yields a bedrock hydraulic conductivity of 4 × 10 -7 m/s. This value is close to the average hydraulic conductivity of 3 × 10 -7 m/s determined from over 100 single-borehole packer tests conducted at the 14 well sites. The near agreement suggests that, at the Mirror Lake site, large-scale hydraulic conductivity can be inferred from a statistical average of many small-scale measurements.

The chlorofluorocarbon and tritium-helium-3 methods were used to determine the ages of water samples collected from packer-isolated intervals in bedrock wells and from a select number of piezometers in the glacial drift. For this purpose, groundwater age is defined as the time between water infiltration into the saturated groundwater system and water collection for analysis. Both methods yield similar ages. Most of the samples are less than 45 years old. However, the spatial distribution of groundwater ages suggests that flow paths are highly complex. Figure 8.5 shows the distribution of groundwater ages in a vertical section on a hillslope through wells R1, TR2, and T1. If the land has a uniform

FIGURE 8.5 Groundwater ages (in years) determined from CFC-12 concentrations at the Mirror Lake study site. From Shapiro and Hsieh (1994).

slope and the subsurface has a uniform hydraulic conductivity, the flow lines should be similar to those illustrated in Figure 8.6. In the vertical direction, ages should increase with depth. Along any flow line, groundwater should be younger near the recharge area (at higher elevations) and older near the discharge area (at lower elevations). In contrast, the observed age distribution in Figure 8.5 is more complex. Younger water is found at several deeper locations and close to

FIGURE 8.6 Expected flow lines for the cross section shown in Figure 8.5, assuming a uniform hillslope and uniform hydraulic conductivity.

an anticipated discharge area. These findings suggest that hillslope topography and bedrock heterogeneity at this site strongly influence groundwater flow paths.

Groundwater samples were also analyzed for major ions, dissolved gases, and a variety of stable and radioactive isotopes. An interesting finding from these analyses is an apparent correlation between alkalinity and groundwater age. Figure 8.7 shows that alkalinity appears to increase with age. That is, water in the glacial till is younger and has a lower alkalinity, whereas water in the bedrock is older and has a higher alkalinity. The higher alkalinity of bedrock water is almost entirely due to the presence of bicarbonate ions (HCO3 - ). Carbon isotope analyses suggest that bicarbonate ions are derived from the dissolution of carbonate minerals such as calcite. However, there is no evidence of calcite on fracture surfaces. Instead, samples of granite from outcrops and cores were found to contain small amounts (approximately one weight percent) of calcite in the rock matrix. This finding suggests that calcite dissolution occurs inside the rock matrix, releasing bicarbonate ions. The bicarbonate ions diffuse from the rock matrix into the fractures, causing an increase in groundwater alkalinity. Because older groundwater has been flowing through fractures for a longer time, it should be higher in alkalinity. This relationship should hold until the alkalinity reaches equilibrium with respect to calcite in the groundwater.

FIGURE 8.7 Plot of groundwater age versus alkalinity of groundwater samples from the Mirror Lake site. From Shapiro and Hsieh (1994).

The importance of matrix diffusion in the evolution of groundwater chemistry is supported by laboratory measurements of rock porosity and diffusion coefficients. Porosities of 32 intact granite samples average 1.5 percent. To measure diffusion in the matrix, a granite sample was soaked in a solution of cesium-137. After 101 days, the cesium-137 was found to have penetrated the granite to a depth of approximately 7 mm. This suggests that over tens of years matrix diffusion is an important mechanism for chemical transport between a fracture and the rock matrix. The calculated effective diffusion coefficient for cesium-137 in the granite matrix is approximately 6 × 10 -13 m 2 /s.

To explore the relationships between alkalinity, groundwater age, and groundwater velocity, a simple model was developed to simulate bicarbonate transport. In the model a flow path in the bedrock is represented by a fracture bounded by intact rock. Groundwater enters the fracture with low alkalinity, characteristic of water in the glacial drift. As the water moves along the fracture, its alkalinity increases because of the incoming flux of bicarbonate ions from the rock matrix (Figure 8.8). The relationship between alkalinity and age is controlled by dissolution of calcite and diffusion of bicarbonate ions in the matrix and the velocity of groundwater in the fracture. Assuming the diffusion coefficient is known from laboratory measurements, the groundwater velocity can be estimated by adjusting its value until the modeled bicarbonate concentration and groundwater age match the measured values for groundwater samples (Figure 8.7). Based on this approach, preliminary analysis suggests that groundwater velocities in the bedrock vary between 10 -3 and 10 -2 m/day.

Discussion

Research at the Mirror Lake site clearly demonstrates the need for an interdisciplinary approach to fractured rock characterization. At the same time, multiple

FIGURE 8.8 Schematic illustration of a simple flow model used to estimate fluid velocities at the Mirror Lake site. The flow path is from left to right in the fracture. Bicarbonate (HCO3/-) ions diffuse into the fracture from the surrounding rock matrix. From Shapiro and Hsieh (1994).

investigation efforts must be coordinated. Detailed studies on the 100-m scale may require the explicit identification and characterization of major (highly transmissive) fractures. Combining fracture detection methods with hydraulic and tracer testing yields a promising approach to accomplishing this objective. Knowledge gained from fracture mapping provides a sound basis for making inferences and for data interpretation. For kilometer-scale investigations, long-term monitoring, groundwater age dating, and geochemical analyses are useful and deserve greater exploitation. The identification of flow paths through a heterogeneous rock environment remains a challenge.

CASE HISTORY II. THE SITE CHARACTERIZATION AND VALIDATION PROJECT: STRIPA MINE, SWEDEN

The Site Characterization and Validation (SCV) Project was performed as a part of the Organization for Economic Cooperation and Development/Nuclear Energy Association's International Stripa Project from 1986 to 1992. The objectives of the project were to test the predictive capabilities of newly developed radar and seismic characterization methods and numerical groundwater models. A basic experiment was designed to predict the distribution of water flow and tracer transport through a volume of granitic rock before and after excavation of a subhorizontal drift (the validation drift) and to compare these predictions with actual field measurements.

A multidisciplinary characterization program was implemented at the SCV site. Because the site was located several hundred meters below the ground surface, all investigations were performed from drifts and boreholes drilled from drifts. The dimensions of the investigated volume were approximately 150 × 150 × 50 m.

The fractures in the drifts adjacent to the SCV site were mapped along scanlines. Maps of the drift walls were made in selected locations. Detailed maps were also made to study the variability in fracturing in fracture zones intersected by several drifts. All boreholes were mapped and oriented by identifying reference fractures from TV logging. The fracture mapping program provided data on fracture orientations, trace lengths, termination modes, and spacing.

Cross-hole and single-hole radar measurements were made to determine the orientation and extent of fracture zones at the site. The directional borehole radar system developed for the project proved particularly useful because it provided data on the orientation of fracture zones based on measurements in a single borehole (see Chapter 4). Radar difference tomography also was used to show how saline tracer injected in a borehole became distributed in the rock mass as it traversed three survey planes.

Seismic techniques were used successfully to determine the orientation and extent of fracture zones. The seismic program included both cross-hole reflection and tomography measurements. The reflection measurements provided the best

data for characterization of the fracture zones. The success of the seismic method was largely due to the application of the Image Space Transform, a novel processing technique developed for the project (Cosma et al., 1991).

To obtain in situ data on the physical properties of the rock in the vicinity of the boreholes, the following logs were run: borehole deviation, sonic velocity, single-point resistance, normal resistivity, caliper, temperature, borehole fluid conductivity, natural gamma radiation, and neutron porosity. The sonic velocity, single-point resistance, and normal resistivity were found to be useful in identifying fractures and fracture zones.

Initially, single-borehole testing was done to provide data on transmissivity and head along the boreholes. Equipment was developed to ensure that reliable information could be collected in the mine environment in reasonable times. The system was built around a multiple-packer probe that allowed rapid testing of permeable features with high spatial resolution. Single-borehole testing was followed by cross-hole testing to define hydraulic properties of the fracture zones on the scale of the site (» 100 m). An important aspect of the cross-hole testing was that it provided a check on the hydraulic properties of the fracture zones identified by using other geophysical techniques. The hydraulic program also included monitoring of head in more than 50 locations across the site. This monitoring provided data on the hydraulic responses to various activities in the mine that could be used to characterize hydraulic connections across the site.

Groundwater samples were taken during hydraulic testing and analyzed for major constituents. The analysis showed that there were three types of groundwater present. These were classified as shallow, mixed, and deep. The groundwater was also found to contain about 3 percent of dissolved gas by volume (at standard temperature and pressure), mainly nitrogen.

An important aspect of groundwater flow through fractures is the effect of stress on fracture transmissivity. Flow through fractures under different stress loads was studied on several samples and in one in situ test. This yielded stress-permeability relationships that were used for modeling studies. Measurements were made, using the overcoring method with a tool called the CSRIO Hollow Inclusion Cell, to determine in situ stresses. At the level of the validation drift, the maximum principal stress was oriented parallel to the drift (i.e., NNW-SSE). It is interesting to note that almost all of the water inflow to the drift was through a single fracture perpendicular to the maximum principal stress.

Characterization of the SCV site was made in several stages. Initial data collection was followed by data interpretation and predictive modeling. Additional boreholes were then drilled to check the predictions based on the initial data set. These new data were then used to refine the conceptual model of the site and groundwater flow predictions. Finally, the predictions were checked by a series of dedicated experiments.

To provide for an adequate description of groundwater flow through the site, the key issue for the characterization work was to identify important flow paths.

In fractured rock environments, fracture zones are normally identified as important permeable hydraulic units this was the working assumption at the onset of the SCV Project. However, the locations, widths, and extents of fracture zones are commonly defined by expert judgment. This can, in many cases, impose a number of problems, as the opinions of experts may vary, and the facts behind a given opinion may be obscure or poorly documented.

An attempt to circumvent this problem and to arrive at a more objective definition of what constitutes a fracture zone was made during the project (Olsson, 1992). A fracture zone index was defined in order to address the following issues:

Is a binary division of the rock mass into ''fracture zones" and "average-fractured rock" appropriate?

Is there an objective method of identifying a fracture zone, and can it be used to define the boundaries of a zone?

Is the arrived-at procedure for fracture zone identifications appropriate for a hydraulic description of the site?

For characterization of a rock volume deep below the ground surface, it is common to base a binary representation of the rock mass on physical properties measured in the vicinity of the boreholes. Hence, the location and width of "fracture zones" can be defined where they intersect boreholes. The extent and geometry of the zones at larger distances from the boreholes can then be probed by using remote sensing methods.

A subset of the data, including normal resistivity, sonic velocity, hydraulic conductivity, coated (and presumably open) fractures, and single-hole radar reflections, was selected for identification of the fracture zones using principal component analysis. First, logarithms were taken of the normal resistivity, sonic velocity, and hydraulic conductivity data. The data were then normalized by subtracting the mean value and dividing by the standard deviation for each parameter. A matrix of correlation coefficients was formed, and the eigenvectors were found for that matrix. Each eigenvector represents a weighting of the data, and new parameters (principal components) were produced by multiplying an eigenvector by the normalized data values. The parameter associated with the largest eigenvalue should represent the most important characteristic of the rock.

For the SCV site the parameter associated with the largest eigenvalue was expected to represent fracturing of the rock. This parameter is referred to as the fracture zone index (FZI). There is essentially only one rock type at the site. Consequently, all observed anomalies in rock properties are caused by fracturing or faulting.

The usefulness of a binary representation of the rock mass can be determined from the frequency distribution of the FZI. Based on the skewed frequency

distribution of the FZI (Figure 8.9), it is justifiable to use a binary description of the rock mass, where average-fractured rock is represented by FZI less than 2 and fracture zones are represented by FZI greater than 2. Using this index, the points in the boreholes that were considered to represent the occurrence of fracture zones could be defined.

The FZI compresses the information from single-hole investigations into a single parameter that describes the most significant properties of the rock (see Figure 8.10). It simplifies interpretation because it allows a single parameter to be used for identification of the anomalous sections in boreholes. Because FZI has been obtained through a quantitative and well-defined procedure, it provides an objective means of classifying the rock into the two classes, averagely fractured rock and fracture zones.

The FZI is also considered to be better for identifying hydraulically significant features than single-hole hydraulic conductivity data alone. The basic reason is that single-hole hydraulic tests yield parameters that are applicable only in a very small volume surrounding the borehole. In the fractured rock at Stripa, hydraulic properties vary by more than an order of magnitude over small distances. Hence, a weighted parameter that incorporates several types of data should be less

FIGURE 8.9 Frequency distribution of FZI (principal component 1). Values for the tail of the distribution (FZI > 2) are designated as "fracture zones," while values less than 2 are designated as "average rock." From Olsson (1992).

FIGURE 8.10 Composite log of the FZI and the single-hole logs used to construct it. The letters at top (H1, Hb, I, and B) indicate major zones correlated between the boreholes. From Olsson (1992).

sensitive to small-scale variations in the rock mass and better for defining the hydraulically important features. In the definition of the FZI, hydraulic conductivity is included as just one of several measurements, and the weighting is determined by the data set itself.

Based on this concept of a binary representation of the rock mass, a procedure was defined for constructing a conceptual model of the site. The procedure is based on identification of fracture zone locations in the boreholes using the FZI and finding the extent of the zones through the use of remote sensing techniques (i.e., radar and seismic techniques). The hydrogeological significance of the geometric model thus obtained was then determined by cross-hole hydraulic testing, which also yielded data on the hydraulic properties of the zones. Further checking of the consistency of the conceptual model was made by comparison with geological and geochemical data. This procedure is iterative and produces lists of identified features, as well as lists of inconsistencies and unexplained anomalies. The procedure is outlined graphically in Figure 8.11.

FIGURE 8.11 Outline of procedure used for construction of the conceptual model of the SCV site. From Olsson (1992).

The conceptual model for the SCV site was found to be consistent with field and test data. Major hydraulic responses were confined to the identified fracture zones, and there were few anomalies in the data that could not be explained. At the site, 80 to 90 percent of the flow was through these fracture zones, as evidenced both by single-hole and cross-hole hydraulic tests. Flow in the fractured rock was dominated by a small fraction of the identified features. Flow in the fracture zones was concentrated in one or two fractures in the zones, and the transmissivity distribution in these fractures was heterogeneous. The hydraulic transmissivity in the fracture zones varied by one to two orders of magnitude over a distance of a meter. Of the fractures in the averagely fractured rock, only a few were found to be transmissive.

Much effort went toward on numerical modeling of groundwater flow and solute transport at the site. Several different models were used. Most included stochastic representations of the permeable features in the rock mass. The conceptual model described above, which provides a deterministic representation of major flow paths, cannot adequately represent the heterogeneity of flow through a fractured rock mass. To achieve more realistic descriptions of the flow system, discrete fracture models were developed and tested. However, to achieve reasonable agreement between predicted and observed flow distributions, it was necessary to include the fracture zones explicitly in the stochastic fracture models.

The SCV Project demonstrated that fracture zones are the dominant groundwater pathways at Stripa and suggested that this may be a common situation in fractured crystalline rock. This finding is consistent with investigations at many other sites in crystalline rock. Work at this site also demonstrated that fracture zones need to be included explicitly in groundwater flow and transport models in crystalline rock. In the SCV Project, procedures were outlined for a quantitative and objective definition of fracture zones. The project demonstrated the capability of radar and seismic techniques to correctly describe the geometry of these zones. It is also evident that the application of these techniques is a prerequisite for constructing a reliable conceptual model for a site. Cross-hole tests should be used to verify the hydraulic significance of geophysically identified fracture zones and to quantify their hydraulic properties. The refined representation of flow heterogeneity requires stochastic modeling techniques. This project demonstrated that data required for stochastic modeling could be collected with a reasonable effort and that discrete fracture network models provide predictions of flow and transport that are in good agreement with observations.

CASE HISTORY III. HYDROCARBON PRODUCTION FROM FRACTURED SEDIMENTARY ROCKS: MULTIWELL EXPERIMENT SITE

The U.S. Department of Energy developed the Multiwell Experiment (MWX) site in order to perform detailed experiments on all aspects of low-permeability

natural gas reservoir evaluation, stimulation, and production (Spencer and Keighin, 1984 Finley and Lorenz, 1987 Lorenz and Finley, 1991). Natural and stimulated fractures are expected to be the primary source of production in these relatively "tight" formations. The MWX site is located in the Piceance Basin of Colorado, about 14 km west-southwest of the town of Rifle. The rocks of interest are primarily sandstones, siltstones, shales, mudstones, and coals of the upper Cretaceous Mesaverde group. At MWX, these strata occur at depths between 1,200 and 2,500 m. The reservoirs in the bottom 250 m of the section consist of marine strandplain sandstones (fossil beach sediments) the overlying rocks are deltaic and fluvial in origin.

The MWX site consists of three closely spaced wells (spacings of 30 to 67 m), from which over 1,200 m of core has been taken about one-third of the core is oriented (Lorenz, 1990). Testing at the site consisted of detailed in situ stress measurements, single-well drawdown and buildup tests, multiwell interference tests, tracer injections, stimulation experiments, and poststimulation production tests. Detailed core analyses and multiple log runs also were performed. Subsequent to MWX, the Department of Energy conducted a follow-up test, named the Slant-Hole Completion Test (SHCT), with the objective of using directional drilling technology to intercept the natural fractures and enhance production. Several hundred feet of core provided additional valuable information about the natural fractures at this site. Primary information about the natural fractures has been derived from the abundant core at this site (Lorenz et al., 1989 Lorenz and Finley, 1991). Two basic types of fractures have been found at the MWX site: extensional fractures in the sandstone and siltstones and shear-type features in the mudstones and shales. Many of the shear-type fractures in the mudstones appear to be dewatering features or other planes of weakness that have accommodated some shear offset and thus display slickenlines. These fractures do not appear to be important for gas production.

The extensional fractures are part of a regional fracture pattern, with essentially all of the fractures being vertical and oriented about N 70° W. The extensional fractures, some of which are incompletely cemented, are the primary production sites from these tight sands the matrix rocks have submicrodarcy permeability, and gas flow from the matrix is not economic. The degree of fracturing is highly depth dependent. There are one to two orders of magnitude more fractures present in core at depths of 1,675 to 1,890 m than from depths greater than 1,980 m. Televiewers were run in these wells to identify fractures, but the high mud weights required to control abnormal formation pressures made them useless for fracture identification. Formation microscanners and televiewers with variable-frequency and focused transducers were not available in the early 1980s when these wells were drilled and cased.

Extensive outcrops of correlative strata exist on the east and west sides of the Piceance Basin, and these have provided ancillary information on the fracture

systems. Figure 8.12 shows a plan view of fractures found in outcrop sandstone and the projection of those fractures into the subsurface, where they would be intersected by boreholes. Clearly, the small orthogonal fractures, which are not seen in core, are relief fractures. The predominant regional extensional fractures are unidirectional, subparallel, and poorly interconnected. Outcrops have also provided data on fracture spacing, length, and height, although these data are possibly affected by relief. The SHCT directional core, however, provides direct evidence of fracture spacings in the subsurface, yielding two populations of fractures, one widely spaced population (1.2 to 2.1 m) and a second population with a spacing of a few centimeters. Spacing is not related to bed thickness in any obvious way.

Field testing of the productive capacity of the fracture systems was performed in eight different intervals of the section (Lorenz, 1989). In the marine sandstones, single-well drawdown/buildup tests yielded permeabilities of 0.15 md and 400 md in two separate intervals. For comparison, in situ matrix permeabilities in

FIGURE 8.12 Plan view illustration of fractures from a sandstone outcrop at the Multi-well Experiment site. The subsurface view shows real data. From Lorenz and Finley (1991).

these zones were only about 0.2 d. Interference tests showed that horizontal permeability anisotropies were on the order of 100:1 owing to the unidirectional nature of the fracture system. Production tests showed that the natural fracture systems are highly stress sensitive. By decreasing the reservoir pressure below a critical value (typically about 6.9 MPa at this site), the production from the well could be almost totally stopped because the decrease in pressure created higher effective confining stresses that physically closed the fractures.

In the fluvial/deltaic sandstones, tests were conducted in six different lenticular reservoirs. Single-well drawdown/buildup tests yielded system total permeabilities of 12 to 50 />d matrix permeabilities measured in core were 0.1 to 2 />d. Figure 8.13 shows a comparison of system permeabilities for various intervals compared to rock matrix permeabilities. Interference tests were conducted in five nonmarine reservoirs, but interference was detected in only one. Tracer injections were conducted in two reservoirs, but only minimal amounts of the tracers were detected in the offset wells, and they were detected in an almost random pattern relative to the pump cycles. The interference patterns suggested permeability anisotropies of 30:1 to 50:1 for most of these reservoirs. Fracture systems in these reservoirs were also stress sensitive, and stimulation experiments showed that they were easily damaged by fracturing fluids. Studies of outcrops of these reservoirs showed that the fractures were limited by lithological variations in the sand bodies, resulting in compartmentalized fracture systems of limited extent, with minimal connections across compartments.

Laboratory experiments on plugs containing fractures were performed for several samples. Mudstone fractures (mostly unmineralized planes of weakness) showed a rapidly decreasing, irreversible loss in conductivity with increasing

FIGURE 8.13 Comparison of system permeabilities to rock matrix permabilities from various intervals in the Multiwell Experiment site. Modified from Lorenz et al. (1989).

stress. Conductivities of fractures in sandstone were also sensitive to changes in stress, but conductivity loss was reversible. One sandstone fracture, however, showed no stress sensitivity whatsoever.

In summary, the natural fractures were found to be the gas production sites in tight sandstone reservoirs. The fractures are unidirectional, of limited extent, and stress sensitive. They are also easily damaged by drilling and completion fluids. Correlation of fracture data from core, outcrop, and various well tests was necessary to define the fracture system and its response to drilling, completion, and production activities.

CASE HISTORY IV. INVESTIGATING THE ANATOMY OF A LOW-DIPPING FRACTURE ZONE IN CRYSTALLINE ROCKS: UNDERGROUND RESEARCH LABORATORY, MANITOBA

In-depth studies of a single large-scale fracture zone are very rare in the literature, and there are relatively few such studies where the results show precisely how groundwater flow through individual fractures relates to the geometry and movement of a fracture zone. One of the most complete studies is the investigation of a fracture zone intersected by a shaft constructed at an Atomic Energy of Canada Limited (AECL) research site on the Canadian Shield. Investigations pertaining to the safety and feasibility of the concept of spent nuclear fuel disposal in plutonic rocks are being conducted at this site at AECL's Underground Research Laboratory (URL). The main working levels of the URL are at depths of 240 and 420 m (240 and 420 levels) with shaft stations at 130 and 300 m (Figure 8.14). Access to the 240-m level is provided by a 2.8 × 4.9 m timber-framed shaft and to the 420-m level by a 4.6-m-diameter circular shaft. Bored (1.83-m-diameter) raises between the surface and the 240 level and between the 240 and 420 levels provide ventilation and alternative access. This section discusses the results obtained from the intensive study of a fracture zone intersected by the URL shaft at about 250 m in depth.

The URL is excavated in the Archean granite of the Lac Du Bonnet Batholith, approximately 120 km northeast of Winnipeg, Manitoba, at the western edge of the Canadian Shield (Figure 8.14). The rocks of the batholith crystallized at a depth 10 to 16 km, approximately 2,670 million years ago, near the close of the regional deformation, which affected the surrounding metavolcanics, metasediments, and gneisses (Everitt et al., 1990). Apart from autointrusive dikes and foliations, there are no significant deformational features in the batholith. The existing fracture network was largely created in the early Proterozoic during cooling and crystallization of the batholith roof zone and in response to ambient regional stresses. Portions of this fracture network were open (reactivated) during regional peneplanation, deposition and then removal of phanerozoic sediments, and subsequent glaciation and deglaciation. However, no new fracture systems are believed to have been formed by these processes (Everitt et al., 1990).

FIGURE 8.14 Location and layout of the Underground Research Laboratory. The location of the Lac Du Bonnet batholith is shaded on the map. On the right are fracture zones 3, 2.5, and 2.

The URL is located near the southern contact of the batholith with the surrounding gneiss. The distribution of xenoliths and deuteric alteration indicates that the present topographic surface is close to the original roof zone of the batholith. The roof zone is marked by shallow-dipping compositional layering (Everitt et al., 1990). The URL access shafts (Figure 8.15) provide a cross section of the roof zone. The geology and fracture distributions in the vicinity of the URL site were extensively investigated by surface and borehole geophysical techniques (Soonawala, 1983, 1984 Wong et al., 1983 Paillet, 1991). These studies showed that the structural geology and hydrogeology of the portion of the batholith surrounding the URL is dominated by a series of southeastward dipping fracture zones (Davison, 1984). Three major low-dipping fracture zones and associated splays were identified at the URL during surface-based drilling and shaft construction. These fracture zones are parallel the shallow-dipping layering of the batholith roof and are generally confined to xenolithic zones or their margins.

FIGURE 8.15 Fracture zones encountered by the URL shaft and their relationship to large-scale distribution of fractures at the URL site. Adapted from Everitt and Brown (1996).

Fracture Zone 2 (FZ2, the primary fracture zone discussed here Figure 8.15) is the dominant member of the low-dipping fault group. Fracture Zone 3 (FZ3) is similar but has less displacement, whereas Fracture Zone 2.5 (FZ2.5) is a splay between these two large fracture zones. A fourth fracture zone (FZ1) is not encountered in the excavations and most boreholes and is not described here. Subvertical fractures are ubiquitous above FZ2.5. Between FZ2.5 and FZ2 they are confined to the fault margins, and they are absent below FZ2 (Everitt et al., 1990 Everitt and Brown, 1996). In general, the fracture zones comprise several chloritic slip surfaces, cataclasite horizon(s), and a variety of smaller-scale fractures and associated alterations extending into the hanging wall and, to a lesser extent, the footwall. The cataclasites consist of recrystallized fault rubble cemented by a fine-grained chlorite-carbonate matrix and are cross-cut by the chloritic slip surfaces, minor fractures, and seams of soft clay-goethite gouge. This assemblage is in varying degrees of groundwater-induced decomposition.

FZ2, FZ2.5, and FZ3 differ in the degree of complexity of their internal fracture patterns, and the extent of fracturing alteration into the adjacent rock. Fracture patterns become simpler, and the extent of fracturing and of alteration is more restricted, with increasing depth. FZ2, the deepest fracture zone intersected by the excavations, comprises a relatively simple system of conjugate shear and extension fractures (the cataclasite zone/chloritic fractures and the antithetic hematite-filled fractures, respectively). Displacement appears to have been dipslip only, with the overlying block moving 7.3 m to the northwest.

The fracture patterns for FZ2.5 and FZ3 are dominated by the same general arrangement of the major slip surfaces, but additional low-dipping and subvertical fracture sets are present. Overall, their geometry suggests two conjugate systems, superimposed to give orthorhombic symmetry, as described by Davis (1984). Reverse dip-slip (up to 1-m throws) dominates in these zones, but strike-slip and oblique-slip lineations also are present. The fracture zones divide the rock mass into a number of tabular-to-wedge-shaped blocks. These blocks are cross-cut by one or more sets of subvertical fractures, the pattern and frequency of which vary from one block (or fracture domain) to the next. The factors influencing the pattern of intrablock fracturing include overall distance from the ground surface, proximity to the bounding faults, and local rock type. The subvertical fractures become less frequent, less continuous, and simpler in pattern with increasing depth. They also become increasingly confined to the immediate margins of the fault zones or to lithological heterogeneities such as dikes. The most prominent set of subvertical fractures parallels the strike of the thrust faults. However, fracture sets oblique or perpendicular to this direction are common above FZ3. Variations in the structure of the fracture zones, and in the fracture domains between them, are illustrated by using the model depicted in Figure 8.15. The northeast face of the model is normal to the strike of the fracture zones as seen in the area of the excavations. FZ2 forms an arcuate outcrop pattern along the south and west sides of the model.

In the block above FZ2, the present-day maximum principal stress is oriented northeast-southwest, parallel to the dominant fracture set and the strike of FZ2. In the shaded area below FZ2, subvertical fracturing is rare or absent, and the maximum principal stress is oriented northwest-southeast, perpendicular to the strike of the thrust fault. The geometry of the thrust faults suggests they were formed when the regional stress field was oriented such that the plane containing the maximum and intermediate principal stresses was subhorizontal, with the former aligned in the northwest-southeast direction. This stress field is believed to be associated with plate accretion on the margins of the Superior craton during the late Archean/early Proterozoic (Everitt et al., 1990). In the case of FZ2, the simple conjugate system of fractures suggests that strain accommodated by fracturing was largely two dimensional. In the case of FZ2.5 and FZ3, however, the orthorhombic pattern of low-dipping major and minor fractures suggests that brittle strain was three dimensional (Davis, 1984). This difference is seen as a consequence of FZ2.5 and FZ3 being ''piggybacked" on FZ2. As such, strike and oblique slip in FZ2.5 and FZ3 are seen as a natural accommodation to displacement on the underlying and dominant thrust fault (FZ2). The subvertical fracture sets are seen as extensional intrablock fracturing that was initiated by geometric flexing and general expansion of the thrust plates in the late Archean to early Proterozoic. The plane containing the maximum and intermediate principal stresses was still subhorizontal, but the local maximum principal stress axis was reoriented and is now aligned northeast-southwest. Reactivation and extension of some fractures likely occurred during Paleozoic transgression, during subsequent removal of the Paleozoic cover, and during repeated continental glaciations. The decreasing frequency, extent, and complexity of subvertical fracturing with depth from the surface are seen as a consequence of both the stacking of the thrust plates and the distance from the surface. The greatest and most varied "flexing" and fracturing would occur in the uppermost blocks. In a single fracture domain the pattern and frequency of subvertical fracturing reflect the distance from, and configuration of, the underlying thrust fault. Between FZ2 and FZ2.5, for example, the pattern of subvertical fractures varies from unimodal to bimodal (orthogonal) as the wedge of rock between FZ2 and FZ2.5 thins to the south. Similar variations are seen in the complexity and preferred orientations of fracturing above FZ2.5, as the plane of FZ3 curves from northeast to north striking.

Hydrogeological studies including single-hole straddle-packer tests and large-scale multiple-borehole hydraulic pressure interference tests conducted before, during, and after shaft construction revealed complex local and regional-scale patterns of permeability in the fracture zones (e.g., Davison and Kozak, 1988 Everitt et al., 1990). In FZ2, permeabilities range over six orders of magnitude, with high and low permeabilities appearing to form distinctive channels at the site scale (Figure 8.16). The prominent northeast-trending transmissivity channel is believed to coincide with the intersection of this fault with FZ2.5. The other channels apparently result from other factors, some of which include

FIGURE 8.16 Hydraulic conductivity variations in FZ2. Modified from Davison and Kozak (1988).

structural controls and hydrogeochemical phenomena, such as the precipitation of different minerals in fillings owing to the mixing of groundwaters with dissimilar chemistries in the fault. In the area of the 240 level, a well-defined isolated region of high transmissivity and low storage is located in the fault immediately northwest of the shaft (Figure 8.17). This region is surrounded entirely by extremely low permeability conditions and has very limited hydraulic communication, with a much more extensive region of high permeability and high storage to the north and west.

These variations in permeability are accompanied by:

Flexures in the fault zone, generalized here by structure contours representing the "middle" of the central cataclasite horizon.

"Anomalies" in the rock-type map of the fault (Figure 8.18) the fracture zone is largely confined to a xenolithic horizon (area 1 in Figure 8.18), but to the west and northwest the zone changes in orientation such that it cross-cuts the layering to intersect the neighboring or gneiss granites.

FIGURE 8.17 Hydraulic conductivity variations in FZ2 in the area of 240 Level. Modified from Davison and Kozak (1988).

Occurrence of core disking in this area that represents locally high in situ stresses adjacent to the fault zone and by variations in the in situ stress normal to the fault zone (Figure 8.19) (in situ stress data from Martin et al., 1990).

It is concluded that the variations in the character and permeability of FZ2, and the variations in the stress magnitudes, are the direct result of undulations in the fault surface. As shown in Figure 8.20, movement on any undulating surface can be expected to result in dilational gaps, restraining bends, fault-bounded structural wedges (such as that between FZ2 and FZ1.9) and secondary subvertical fractures in the fault-bounded blocks. Variations in relative permeability in the fracture zone are reflected by corresponding variations in the thickness of the alteration halo. This correlation is a useful one because it serves as a qualitative indicator of historic flow variation, which in turn has practical application in the layout of characterization drilling.

The subvertical fracture shown in Figure 8.20 is a wedge-shaped zone of fractures that begins at the base of FZ2.5 and narrows downward until it terminates at the 240 level, about 35 m above FZ2. It parallels the strike of FZ2 and is known to extend 35 m vertically and at least 105 m horizontally. This fracture is interpreted as having formed in response to flexing of the fault block owing

FIGURE 8.18 Map of litho-structural domains crossed by FZ2.

to the change in dip angle of the fault directly beneath it. Such flexing would have led, at least locally, to a reorientation of the principal stresses. The maximum principal stresses below and above the fault zone are perpendicular and parallel, respectively, to the strike of the thrust fault (Everitt et al., 1990). The stress field above the thrust fault is oriented such that the subvertical fractures in this area are open and conductive. Extensive efforts to characterize the geology, hydrogeology, and geomechanical characteristics of this major thrust fault have led to the following conclusions:

Complex patterns of permeability exist in FZ2 at the scale of the site and at the scale of the excavations. These patterns include channels of high or low permeability that alternate along the strike of the fault.

The variations in permeability appear to correlate with undulations in the plane of the fracture zone, which in turn correlate with dilational gaps (the high-conductivity channels), restraining bends (the areas of core disking and high normal stresses), and fault-bounded structural wedges and secondary fractures in the fault-bounded blocks.

These interpretations are based on the compilation of geological, hydrogeological, and geomechanical data and emphasize the need for an integrated multi-

FIGURE 8.19 Areas of disking and measured normal stresses. From Martin et al. (1990).

disciplinary approach to characterizing permeability variations in a fractured medium.

CASE HISTORY V. FRACTURE STUDIES IN A GEOTHERMAL RESERVOIR: THE GEYSERS GEOTHERMAL FIELD, CALIFORNIA

The Geysers geothermal field in central California (Figure 8.21) is one of the best-known geothermal reservoirs in North America and one where steam production is associated with fractures and faults in otherwise low-permeability metasedimentary and hypabyssal plutonic rocks. This field is one of the most thoroughly studied geothermal reservoirs in the world. However, the characteristics and hydraulic properties of fractures are only partially understood at even this well-studied site for a variety of reasons common to most geothermal study sites: (1) complexity of the local geology (2) difficulty of geological mapping and geophysical soundings in a deeply weathered and rugged terrain (3) problems in obtaining well logs and other measurements in hostile borehole environments and (4) difficulties in modeling two-phase flow in heterogeneous, dual-porosity reservoirs. Despite these difficulties, the results from ongoing studies at The Geysers provide examples of how geological, geochemical, geophysical, and reservoir modeling techniques can be applied to one of the most difficult problems in fracture hydrology.

FIGURE 8.20 Cross section through fracture zones 2 and 2.5, with the subvertical "room 209 fracture."

The Geysers geothermal field is located in the Coast Ranges province of central California. Because of the difficulty in obtaining geophysical soundings in this rugged and geologically complex terrain, models of The Geysers geothermal reservoir have been developed mostly from surface geological and structural investigations and from detailed study of borehole cuttings and cores. Surface investigations reveal a series of northwest-trending, steeply dipping, strike-slip faults superimposed on previously faulted and folded terrain. Reservoir rocks consist of blueshist- and greenshist-grade metasedimentary rocks of the Franciscan assemblage intruded by a large felsic pluton that appears genetically related to late Tertiary and Quaternary surficial rhyolites of the Clear Lake volcanic field, which lies just northeast of the geothermal reservoir (McLaughlin and Donnelly-Nolan, 1981). The reservoir itself is located beneath relatively impermeable caprocks and is developed in both the pluton and overlying Franciscan metagraywackes and argillites (Figure 8.21). The intrusive "felsite" is at least 1.3 million years ago (Schriener and Suemnicht, 1981 Dalrymple, 1992). The reservoir is believed to have developed in the graywacke because of its intrinsic brittleness and high susceptibility to fracturing and because of hydrothermal dissolution of Franciscan calcite, aragonite, and other minerals that were only

FIGURE 8.21 Sketch map (top) and schematic cross sections (middle and bottom) of the geothermal reservoir at The Geysers geothermal field. From Thompson (1992).

partially filled by late-stage secondary phases (Gunderson, 1990 Hulen et al., 1992). The heat source for the geothermal system is believed to be from felsite intrusions beneath the reservoir (Hebein, 1985 Walters et al., 1988).

Surface geophysical measurements yield some information about the nature of the geothermal reservoir and underlying rocks, but the complexity of the terrain and geological environment have made these measurements very difficult to interpret. Gravity measurements indicate a pair of negative anomalies associ-

ated with the reservoir (Chapman, 1978 Chapman et al., 1981 Isherwood, 1981). The larger and presumably deeper anomaly is centered northeast of the field and is believed to be associated with a magmatic body at depth below the Clear Lake volcanic field. A smaller, shallower gravity low (the "production low") is apparently associated with the geothermal reservoir itself. The local density deficiency is attributed to a combination of effects, including fluid withdrawal, the presence of steam in the reservoir, geochemical dissolution of minerals, and the presence of relatively less dense minerals in reservoir rocks (Denlinger, 1979 Denlinger and Kovach, 1981). Aeromagnetic surveys generally confirm the structure indicated by the gravity data and help further define the lateral limits of the reservoir. Surface resistivity measurements have done little more than confirm the separation of the subsurface environment into three layers: basement, reservoir, and cap rock (Keller and Jacobson, 1983 Keller et al., 1984).

Passive seismic surveys have been especially useful in defining reservoir properties, based on both identification of source areas for microseismic events and characterization of reservoir volumes through which such seismic waves pass (Iyer et al., 1979 Majer and McEvilly, 1979). The seismic source area maps indicate the location of a magma chamber at a depth of several kilometers to the northeast. The elevated level of seismic activity may be associated with fluid withdrawal from the reservoir (Young and Ward, 1981). Seismic activity in the reservoir provides an important constraint on geomechanical models of the reservoir. The most frequently cited mechanism for the generation of this activity is the response of the fractured rock to compression as steam is withdrawn (Hamilton and Muffler, 1972 Majer and McEvilly, 1979). Most recent studies indicate that microseismic activity is closely associated with both injection and withdrawal of fluids (Majer et al., 1988 Stark, 1990).

Active seismic surveys have been very difficult to carry out and have done little more than confirm the stratigraphy and faults inferred from drilling. Coupling of source energy to the ground surface has been a continuing problem. Most effective surface seismic surveys have used the Vibroseis method, which was designed to improve seismic sounding in such terrains (Denlinger and Kovach, 1981). Even with this method, most energy is apparently scattered in the reservoir volume. The few weak deep reflections probably represent the top of the basement. However, the microseismic monitoring technique has been much more effective in delineating the properties of reservoir rocks in part because the energy source is well coupled to the rock mass. These surveys indicate that the developed reservoir volume is associated with relatively low Vp/Vs ratios (ratios of compressional to shear velocity). This implies a reduced value for Poisson's ratio of reservoir rocks from which fluids have been withdrawn (O'Connell and Johnson, 1991). A similar result was obtained in vertical seismic profile studies reported by Majer et al. (1988).

Geochemical investigations generally form a major part of geothermal reservoir studies, and this is certainly true of The Geysers. Patterns of geochemical

alteration of reservoir rocks and minerals deposited in fracture fillings indicate that the reservoir has evolved from a liquid-dominated to a vapor-dominated system (Sternfeld, 1989). This has apparently occurred in part because the relatively impermeable caprock and sealed margins of the system inhibited recharge of the reservoir (White et al., 1971). Much of the geochemical and thermal history of the reservoir and caprock is based on interpretation of fluid inclusions in core samples and the compositions, textures, and paragenesis of minerals deposited in fractures, breccias, and dissolution cavities (Walters et al., 1988 Hulen et al., 1991). This result has important consequences for fracture studies. The complex evolution of a geothermal reservoir is important in evaluating the coupling between flow, temperature, stress, and fluid chemistry. Depending on location, the caprock is also a consequence of stratigraphy and the interaction of stress, temperature, and mineral deposition.

Geomechanical investigations have also contributed to the study of the reservoir. Much of this work centers on definition of the geomechanical nature of the reservoir and is concerned with questions about the effects of structural control on the lateral continuity of permeable zones and the flow of steam toward production wells. Fault and fracture orientation may be the primary determinant of flow in the reservoir (Thompson and Gunderson, 1989 Beall and Box, 1992). Several models have been proposed for the generation of open fractures in the reservoir, including wrench faulting of blocks and opening of near-vertical fractures and faults in the direction of minimum horizontal stress (Oppenheimer, 1986 Thompson and Gunderson, 1989 Nielson and Brown, 1990). At least some oriented cores indicate that the strike of fractures is perpendicular to the present direction of the least principal stress (Nielson and Brown, 1990). Other data indicate a strong lithological control on fracture generation or preservation in some cores, graywacke beds are fractured, but intervening argillite beds are not (Sternfeld, 1989 Hulen et al., 1991). Production data indicate that there is horizontal continuity between producing wells. Fracture generation and opening mechanisms need to account for this horizontal continuity as well as the presence of conduits for the upward convection of fluids.

Observations of fractures, veins, and the texture of core samples have further contributed to an understanding of the source and movement of fluids in the reservoir. A double-porosity framework has been applied to the reservoir (Williamson, 1990). Major flow conduits are assumed to be fractures, faults, and brecciated zones, although only a single example of a major steam conduit has been recovered from core (Gunderson, 1990). The bulk of fluid reserves in the reservoir is stored in "matrix" porosity, where the matrix refers to everything besides the main fluid conduits. Detailed core examination reveals that the matrix porosity consists of open microfractures, dissolution voids from leaching of calcite and aragonite, and vuggy hydrothermal veinlets (Gunderson, 1990 Hulen et al., 1992). Much of the reservoir production apparently comes from water

adsorbed on the surfaces of minerals lining pore spaces and veins (Barker et al., 1992).

One of the most effective methods for investigating the flow of water and steam along fractures in the reservoir is production testing and tracer studies. Fluids injected into the reservoir appear to preferentially follow planes perpendicular to the direction of the least principal stress (Thompson and Gunderson, 1989). In the past, tritium and deuterium from power plant injectate have been used as tracers in attempting to follow the path of injected water from injection to production wells (Gulati et al., 1978). These tracers are difficult to interpret because relatively high detection limits are required and the effects of vapor fractionation on the tracers in the reservoir are unknown. Recent studies have used halogenated alkenes, which fractionate almost exclusively into steam and have extremely low detection limits (Adams et al., 1991a,b). Vapor-phase tracers have been detected in production wells within days of injection, indicating horizontal velocities in the reservoir as large as 1 km/day (Adams et al., 1991a,b). The path traveled by the first few percent of steam generated from injection water appears to be the same as that indicated for the injection water using deuterium tracers. The extremely short travel times indicate that flow takes place along major fractures and faults, rather than through the "matrix" porosity of the bulk of the reservoir rock.

These results demonstrate the way in which various lines of investigation can be used to constrain one of the most complicated problems related to fracture flow&mdashdelineation and modeling of flow in geothermal reservoirs. The difficulty in obtaining measurements in a complex geological environment, the hostile environment of boreholes, and the multivariate nature of two-phase flow in fractured media combine to make such studies extremely difficult to carry out. One of the most interesting aspects of fracture studies in geothermal reservoirs is the interaction of temperature, stress, and geochemistry in controlling flow. Stress and temperature determine mechanical properties, and temperature and geochemistry determine where mineral dissolution and growth occur. These interrelationships allow for many possible kinds of behavior. One of the most important examples is the generation of a caprock. If these zones of sealed fractures were in fact formed during the evolution of geothermal systems, the fracture infilling clearly influences the distribution of temperature in the reservoir as well as the geometry of convective flow.

The number of independent variables in such geomechanical investigations requires that the full array of potential measurements be applied. This overview of investigations at The Geysers geothermal area provides an example of the techniques that can be applied to these difficult investigations and the various models that can be developed in attempting to constrain a multivariate, two-phase, dual-porosity fracture flow problem where reservoir porosity and permeability are a time-varying function of temperature, pressure, and in situ stress conditions.

REFERENCES

Adams, M. C., J. M. Moore, and P. Hirtz. 1991a. Preliminary assessment of halogenated alkanes as vapor-phase tracers. Paper presented at the Sixteenth Annual Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, Calif., pp. 57&ndash62.

Adams, M. C., J. J. Beall, S. L. Enedy, and P. Hirtz. 1991b. The application of halogenated alkanes as vapor-phase tracers: a field test in the southeast Geysers. Geothermal Resources Council Transactions, 15:457&ndash463.

Andersson, J. E., P. Andersson, and E. Gustafsson. 1991. Effects of gas-lift pumping on borehole hydraulic conditions at Finnsjön, Sweden. Journal of Hydrology, 126(1&ndash2):113&ndash127.

Andersson, K. P., P. M. Andersson, E. Gustafsson, and O. Olsson. 1989. Mapping ground water flow paths in crystalline bedrock using differential radar crosshole tomography measurements utilizing saline tracers. In Proceedings of the Third International Symposium on Borehole Geophysics for Minerals, Geotechnical, and Groundwater Applications. Tulsa, Okla.: Society of Professional Well Log Analysts.

Barker, B. J., M. S. Gulati, M. A. Bryan, and K. L. Reidel. 1992. Geysers reservoir performance. Monograph on The Geysers Geothermal Field. Special report no. 17, Geothermal Resource Council, Davis, Calif., pp. 167&ndash178.

Barton, C. C., and P. A. Hsieh. 1989. Physical and hydrologic-flow properties of fractures. Field Guide Book T385, American Geophysical Union, Washington, D.C., 36 pp.

Barton, C. C., and E. Larsen. 1985. Fractal geometry of two-dimensional fracture networks at Yucca Mountain, southwest Nevada. Pp. 77&ndash84 in Fundamentals of Rock Joints, O. Stephansson, ed. Lulea, Sweden: Centek Publishers.

Bassett, R. L., S. P. Neumann, T. C. Rasmussen, A. Guzman, G. R. Davidson, and C. F. Lohrstorfer. 1994. Validation studies for assessing unsaturated flow and transport through fractured rock. Report NUREG/CR-6203, prepared by the University of Arizona, Tucson, for the U.S. Nuclear Regulatory Commission.

Bassett, R. L., E. L. Fitzmaurice, and A. Guzman. 1996. Rapid and long-distance transport of water and solute through networks in variably saturated tuff. Submitted to Water Resources Research.

Beall, J. J., and W. T. Box, Jr. 1992. The nature of steam-bearing fractures in the South Geysers Reservoir. Pp. 69&ndash75 in Monograph on The Geysers Geothermal Field. Special report no. 17, Geothermal Resource Council, Davis, Calif.

Beauheim, R. L. 1988. Scale effects in well testing in fractured media. Pp. 152&ndash161 in Proceedings of the 4th Canadian/American Conference on Hydrogeology, B. Hitchon and S. Bachu, eds. Dublin, Oh.: National Water Well Association.

Block, L., C. H. Cheng, M. Fehler, and W. S. Phillips. 1994. Seismic imaging using microearthquakes induced by hydraulic fracturing. Geophysics, 59:102&ndash112.

Bredehoeft, J. D., C. E. Neuzil, and P. C. D. Milly. 1983. Regional flow in the Dakota aquifer: a study of the role of confining layers . Water Supply Paper 2237, U.S. Geological Survey, Reston, Va.

Busenberg, E., and L. N. Plummer. 1992. Use of chlorofluorocarbons (CC13F and CC12F2) as hydrologic tracers and age-dating tools: the alluvium and terrace system of central Oklahoma. Water Resources Research, 28 (9):2257&ndash2283.

Chapman, R.H. 1978. Gravity anomalies in The Geysers-Clear Lake Area, Northern California, Field Trip Guidebook 45, Castle Steam Field, Great Valley Sequence. Pp. 89&ndash98 in 53rd Annual Meeting, Pacific Section, American Association of Petroleum Geologists, Society of Economic Paleontologists and Mineralogists, and Society of Exploration Geophysicists, Sacramento, Calif.

Chapman, R. H., R. P. Thomas, H. Dykstra, and L. D. Stockton. 1981. A reservoir assessment of The Geysers geothermal field. Publication TR 27, California Division of Oil and Gas, Sacramento, Calif., pp. 21&ndash33.

Chem-Nuclear Systems, Inc. 1993. Site characterization report for the Wake/Chatham County potentially suitable site, North Carolina. Raleigh, N.C.: Chem-Nuclear Systems, 85 pp.

Cosma, C., P. Heikkinen, and S. Pekonen. 1991. Improvement of high resolution borehole seismics. Stripa Project TR 913, Swedish Nuclear Fuel and Waste Management Co., Stockholm.

Dalrymple, G. B. 1992. Preliminary report on 40Ar/39Ar incremental heating experiments on feldspar samples from the telsite unit, Geysers geothermal field, California. USGS Open-File Report 92&ndash407, U.S. Geological Survey, Reston, Va., 15 pp.

Davies, P. B., L. H. Brush, and F. T. Mendenhall. 1991. Assessing the impact of waste-generated gas from the degradation of transuranic waste at the Waste Isolation Pilot Plant. In Proceedings of the Workshop on Gas Generation and Release from Radioactive Waste Repositories, Aixen-Provence, France, September 23-26. Washington, D.C.: Nuclear Regulatory Commission.

Davis, G. H. 1984. Structural Geology of Rocks and Regions. New York: John Wiley & Sons.

Davison, C. C. 1984. Monitoring hydrogeological conditions in fractured rock at the site of Canada's Underground Research Laboratory. Groundwater Monitoring Review, 3(4):95&ndash102.

Davison, C. C., and E. T. Kozak. 1988. Hydrogeological characteristics of fracture zones in a granite batholith of the Canadian Shield. Pp. 53&ndash59 in Proceedings of the 4th Canadian/American Conference on Hydrogeology. B. Hitchon and S. Bachu, eds. Dublin, Oh.: National Water Well Association.

Denlinger, R. P. 1979. Geophysics of The Geysers geothermal field, northern California. Ph.D. thesis, Stanford University, Stanford, Calif., 87 pp.

Denlinger, R. P., and R. L. Kovach. 1981. Three-dimensional gravity modeling of The Geysers hydrothermal system and vicinity, northern California: Geological Society of American Bulletin, Pt. 1, 92(6):404&ndash410.

Everitt, R. A., and A. Brown. 1996. Geological mapping of the AECL Research's Underground Research Laboratory&mdashA cross section of thrust faults and associated fractures in the roof zone of an Archean batholith. In Fractured and Jointed Rock Masses. Rotterdam: A. A. Balkema.

Everitt, R. A., A. Brown, C. C. Davison, M. Gascoyne, and C. D. Martin. 1990. Regional and local setting of the Underground Research Laboratory. Pp. 64-1&ndash64-23 in Proceedings of the International Symposium on Unique Underground Structures. Golden, Colo.: Colorado School of Mines.

Fehler, M. 1989. Stress control of seismicity patterns observed during hydraulic fracturing experiments at the Fenton Hill hot dry rock geothermal energy site, New Mexico. International Journal of Rock Mechanics and Mining Science and Geomechanics Abstracts, 26:211&ndash219.

Finley, S. J., and J. C. Lorenz. 1987. Significance of drilling and coring-induced fractures in Mesaverde core, northwestern Colorado. Sandia National Laboratories, AAPG Bulletin, 71(5):556.

Geldon, A. L. 1993. Preliminary hydrogeologic assessment of boreholdes UE-25 C-1, UE-25 C-2, UE-25 C-3, Yucca Mountain, Nye City, Nevada. USGS Water Resources Investigations Report 92-4016, U.S. Geological Survey, Reston, Va.

Geothermal Resources Council. 1992. Monograph on The Geysers geothermal field. Special Report No. 17, Geothermal Resources Council, Davis, Calif., 325 pp.

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Gunderson, R.P. 1990. Reservoir matrix porosity at The Geysers from core measurements. Geothermal Resources Council Transactions, 14:449&ndash454.

Gustafsson, E., and P. Andersson. 1991. Groundwater flow conditions in a low-angle fracture zone at Finnsjön, Sweden. Journal of Hydrology, 126(1&ndash2):79&ndash11.

Hamilton, R. M., and L. M. P. Muffler. 1972. Microearthquakes at The Geysers geothermal area, California. Journal of Geophysical Research, 77(11):2081&ndash2086.

Hardin, E. L., C. H. Cheng, F. L. Paillet, and J. D. Mendelson. 1987. Fracture characterization by means of attenuation and generation of tube waves in fractured crystalline rock at Mirror Lake, New Hampshire. Journal of Geophysical Research, 92(B8):7989&ndash8006.

Hebein, J. J. 1985. Historical hydrothermal evolutionary facets revealed within the exploited Geysers steam field. Geothermal Resources Council Bulletin, 14(6):13&ndash16.

Hsieh, P. A., and A. M. Shapiro. 1994. Hydraulic characteristics of fractured bedrock underlying the FSE well field at the Mirror Lake site, Grafton County, New Hampshire. In U.S. Geological Survey Toxics Substance Hydrology Program, D. W. Morganwalp and D. A. Aronson, eds., Proceedings of the technical meeting, Colorado Springs, Colorado, Sept. 20&ndash24, 1993. USGS Water-Resources Investigations Report, U.S. Geological Survey, Reston, Va.

Hsieh, P. A., S. P. Neuman, and E. S. Simpson. 1983. Pressure testing of fractured rocks&mdasha methodology employing three-dimensional hole test. NUREG/CR-3213, U.S. Nuclear Regulatory Commission, Washington, D.C., 176 pp.

Hsieh, P. A., A. M. Shapiro, C. C. Barton, F. P. Haeni, C. D. Johnson, C. W. Martin, F. L. Paillet, T. C. Winter, and D. L. Wright. 1993. Methods of characterizing fluid movement and chemical transport in fractured rock. In Field Trip Guide Book for Northeastern United States, J. T. Chaney and J. C. Hepburn, eds. Boulder, Colo.: Geological Society of America.

Hulen, J. B., D. L. Nielson, and W. Martin. 1992. Early calcite dissolution as a major control on porosity development in The Geysers steam field, California&mdashadditional evidence in core from Unocal well NEGU-17. Geothermal Resources Council Transactions, 16:167&ndash174.

Hulen, J. B., M. A. Walters, and D. L. Nielson. 1991. Comparison of reservoir and caprock core from the northwest Geysers steam field, California&mdashimplications for development of reservoir porosity. Geothermal Resources Council Transactions, 15:11&ndash18.

Isherwood, W. F. 1981. Geophysical overview of The Geysers. Pp. 83&ndash95 in Research in the Geysers-Clear Lake area, northern California, R. J. McLaughlin and J. M. Donnelly-Nolan, eds., USGS Professional Paper 1141, U.S. Geological Survey, Reston, Va.

Iyer, H. M., D. H. Oppenheimer, and T. Hitchcock. 1981. Abnormal P-wave delays in The Geysers-Clear Lake geothermal area. Science, 204:495&ndash497.

Kamineni, D. C., and M. Bonardi. 1983. Bastnaesite in fractures of the Eye-Dashwa lakes pluton, Atikokan, Ontario, Canada. Chemical Geology, 39:263.

Kamineni, D. C., G. F. McCrank, and D. Stone. 1987. Multiple alteration events in the East Bull Lake anorthosite-gabbro layered complex, NE Ontario, Canada: evidence from fracture mineralogy and 40AR-39AR dating. Applied Geochemistry, 2:73&ndash80.

Keller, G. V., and J. J. Jacobson. 1983. Deep electromagnetic soundings northeast of The Geysers steam field. Geothermal Resources Council Transactions, 7:497&ndash603.

Keller, G. V., J. I. Pritchard, J. J. Jacobson, and N. Harthill. 1984. Megasource time-domain electromagnetic sounding methods. Geophysics, 49:993&ndash1009.

Kim, K., and W. M. McCabe. 1984. Geomechanics characterization of a candidate nuclear waste repository site in basalt. Proceedings of the 25th Symposium on Rock Mechanics, Northwestern University, pp. 1126&ndash1135.

Lapcevic, P. A., K. W. Novakowski, and F. L. Paillet. 1993. Analysis of transient flow in an observation well intersecting a single fracture. Journal of Hydrology, 151:227&ndash239.

Laubach, S. E. 1988. Subsurface fractures and their relationship to stress history in East Texas Basin sandstone. Techtonophysics, 156(1-2):37&ndash49.

Laubach, S. E., R. W. Baumgardner, Jr., E. R. Monson, E. Hunt, and K. J. Meador. 1988. Fracture detection in low-permeability reservoir sandstone a comparison of BHTV and FMS logs to core. SPE-18119, Society of Petroleum Engineers of AIME, Richardson, Tex., pp. 129&ndash139.

Lorenz, J. C. 1989. Difference in fracture characteristics and related production, Mesaverde formation, northwestern Colorado. Sandia National Laboratories, SPE Formation Evaluation, 4(1):11-16.

Lorenz, J. C. 1990. Significance of coring-induced fractures in Mesaverde core, northwestern Colorado. Sandia National Laboratories, AAPG Bulletin, 74(7):1017&ndash1029.

Lorenz, J. C., and S. J. Finley. 1991. Regional fractures. II. Fracturing of Mesaverde reservoirs in the Piceance Basin, Colorado. Sandia National Laboratories, AAPG Bulletin, 75(11):1738&ndash1757.


Details

Michael Ashby

Royal Society Research Professor Emeritus at Cambridge University and Former Visiting Professor of Design at the Royal College of Art, London, UK

Mike Ashby is sole or lead author of several of Elsevier’s top selling engineering textbooks, including Materials and Design: The Art and Science of Material Selection in Product Design, Materials Selection in Mechanical Design, Materials and the Environment, and Materials: Engineering, Science, Processing and Design. He is also coauthor of the books Engineering Materials 1&2, and Nanomaterials, Nanotechnologies and Design.

Affiliations and Expertise

Royal Society Research Professor Emeritus, University of Cambridge, and Former Visiting Professor of Design at the Royal College of Art, London, UK


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