Understanding hydraulic fracturing: a multi-scale problem.

Despite the impact that hydraulic fracturing has had on the energy sector, the physical mechanisms that control its efficiency and environmental impacts remain poorly understood in part because the length scales involved range from nanometres to kilometres. We characterize flow and transport in shale formations across and between these scales using integrated computational, theoretical and experimental efforts/methods. At the field scale, we use discrete fracture network modelling to simulate production of a hydraulically fractured well from a fracture network that is based on the site characterization of a shale gas reservoir. At the core scale, we use triaxial fracture experiments and a finite-discrete element model to study dynamic fracture/crack propagation in low permeability shale. We use lattice Boltzmann pore-scale simulations and microfluidic experiments in both synthetic and shale rock micromodels to study pore-scale flow and transport phenomena, including multi-phase flow and fluids mixing. A mechanistic description and integration of these multiple scales is required for accurate predictions of production and the eventual optimization of hydrocarbon extraction from unconventional reservoirs. Finally, we discuss the potential of CO2 as an alternative working fluid, both in fracturing and re-stimulating activities, beyond its environmental advantages.This article is part of the themed issue 'Energy and the subsurface'.

CO2/Brine transport into shallow aquifers along fault zones.

Unintended release of CO(2) from carbon sequestration reservoirs poses a well-recognized risk to groundwater quality. Research has largely focused on in situ CO(2)-induced pH depression and subsequent trace metal mobilization. In this paper we focus on a second mechanism: upward intrusion of displaced brine or brackish-water into a shallow aquifer as a result of CO(2) injection. Studies of two natural analog sites provide insights into physical and chemical mechanisms controlling both brackish water and CO(2) intrusion into shallow aquifers along fault zones. At the Chimayó, New Mexico site, shallow groundwater near the fault is enriched in CO(2) and, in some places, salinity is significantly elevated. In contrast, at the Springerville, Arizona site CO(2) is leaking upward through brine aquifers but does not appear to be increasing salinity in the shallow aquifer. Using multiphase transport simulations we show conditions under which significant CO(2) can be transported through deep brine aquifers into shallow layers. Only a subset of these conditions favor entrainment of salinity into the shallow aquifer: high aspect-ratio leakage pathways and viscous coupling between the fluid phases. Recognition of the conditions under which salinity is favored to be cotransported with CO(2) into shallow aquifers will be important in environmental risk assessments.

Multicomponent interparticle-potential lattice Boltzmann model for fluids with large viscosity ratios.

This work focuses on an improved multicomponent interparticle-potential lattice Boltzmann model. The model results in viscosity-independent equilibrium densities and is capable of simulating kinematic viscosity ratios greater than 1000. External forces are incorporated into the discrete Boltzmann equation, rather than through an equilibrium velocity shift as in the original Shan and Chen (hereafter, SC) model. The model also requires the derivation of a momentum conserving effective velocity, which is substituted into the equilibrium distribution function and applies to both the single- and multiple-relaxation-time formulations. Additionally, higher-order isotropy is used in the calculation of the fluid-fluid interaction forces to reduce the magnitude of spurious currents (i.e., numerical errors) in the vicinity of interfaces. First, we compare the model to the SC model for static bubble simulations. We demonstrate that the model results in viscosity-independent equilibrium bubble densities for a wide range of kinematic viscosities, which is not the case for the SC model. Furthermore, we show that the model is capable of simulating stable bubbles for kinematic viscosity ratios greater than 1000 (when higher-order isotropy is used), whereas the SC model is known to be limited to kinematic viscosity ratios on the order of 10. Next we verify the model for surface tension via Laplace's law and show that the model results in the same surface tension values for a range of kinematic viscosities and kinematic viscosity ratios of 10, 100, and 1000. The model is also verified for layered cocurrent flow though parallel plates. We show that the simulated velocity profiles preserve continuity at the interface for kinematic viscosity ratios ranging from 0.001 to 1000 and that the model accurately predicts nonwetting and wetting phase relative permeability for kinematic viscosity ratios of 0.01 to 100.

HIV prevention in primary care: impact of a clinical intervention.

Discomfort, lack of confidence in skills, and environmental constraints may cause primary care providers to miss opportunities to discuss human immunodeficiency virus (HIV) risk with patients. We used a systems approach to address both intrapersonal and environmental barriers to HIV risk assessment and prevention counseling in a managed care clinical setting. The design was one-group pretest/posttest. The study took place in two primary care clinics of a large Pacific Northwest managed care organization. Participants (n = 49) included physicians, physician assistants, nurse practitioners, registered nurses, and social workers. The intervention included training, clarification of provider/staff roles, assess to tools and materials, and reminders/reinforcers. Outcome measures were provider attitudes, beliefs, outcome expectations, knowledge, confidence in skills, and perceived supports and barriers, measured by written pretest/posttest surveys administered 12 months apart. Seven months after the most intensive part of the intervention, providers' attitudes and beliefs were more favorable to HIV risk assessment and prevention counseling. They were less likely to express frustration with high-risk patients (decrease from 100% to 79% agreement, p = 0.001) and more confident that their advice would be effective with gay men and single adult heterosexuals (p = 0.002 and 0.005, respectively). They reported more confidence in their training in sexual history taking (p = 0.0003) and their skills assessing readiness for change (p = 0.007), and more support in practice environments. This study demonstrated that it is possible to affect important personal and environmental factors that influence primary care providers' HIV prevention behavior using an interactive, real-world systems approach. Further research is needed on providers' impact on patient behavior.

Enhancing primary care HIV prevention: a comprehensive clinical intervention.

CONTEXT: Human immunodeficiency virus (HIV) and sexually transmitted disease (STD) risk assessment and counseling are recommended for a large proportion of the population, yet measured rates of such counseling remain low. OBJECTIVE: Use a comprehensive intervention to improve and sustain rates of HIV/STD risk assessment and counseling by providers. DESIGN: Patient telephone survey using a one-group pre- and post-intervention design with measurements over a 62-week period. SETTING AND PARTICIPANTS: Patients (N=1042) from two outpatient clinics at a health maintenance organization (HMO) presenting for either of two types of index visit: symptomatic (n=210), or routine physical examination or birth control (n=832) visits. MAIN OUTCOME MEASURES: Telephone survey performed within 3 weeks of the index visit. Patients' recall of a general discussion of HIV/STDs and specific discussion of sexual behaviors/risk factors. RESULTS: The intervention was associated with increased patient recall of providers: discussing HIV/STD in general (OR 1.6; 95% CI, 1.12-2.22), asking about sexual behaviors/risk factors (OR 1.7; 95% CI, 1.2-2.6), discussing HIV prevention generally (OR 2.4; 95% CI, 1.4-4.0), and discussing personal risk reduction (OR 2.6; 95% CI, 1.6-4.3). Provision of written materials concerning HIV/STD also increased significantly (OR 2.8; 95% CI, 1.3-4.3). A clear-cut pattern of improved provider effort was seen, with the most pronounced improvements in high-risk patients. Results were stable over a 38-week follow-up period. CONCLUSION: A sustained improvement in HIV/STD risk assessment and counseling can be achieved in an outpatient HMO setting using a relatively non-intensive systematized intervention.

Hospital course of HIV-positive patients with odontogenic infections.

OBJECTIVE: The study purpose was to compare and contrast the hospital course of patients who are human immunodeficiency virus-positive (HIV+) and human immunodeficiency virus-negative (HIV-) who were admitted to manage their odontogenic infection. STUDY DESIGN: We used a retrospective case-control study design and a sample derived from patients admitted for management of their odontogenic infections. Cases and controls were defined as patients who were HIV+ or HIV-, respectively. HIV status was determined by patient self-report. Outcome variables included admission temperature (degrees Celsius) and white blood cell count, number of fascial spaces infected, days with temperature >38 degrees C, need for intensive care, and length of hospital stay. RESULTS: The study sample consisted of 60 patients (10 HIV+ cases and 50 HIV- controls matched for age and sex) with a mean age of 32.8 +/- 6.6 years and was predominantly male (78%). Significant differences existed between patients who were HIV+ and those who were HIV- for the following variables: admission white blood cell count, number of days with maximum temperature >38.0 degrees C, and use of the intensive care unit. CONCLUSIONS: The study results suggest that patients who are HIV+ who are admitted for management of odontogenic infection have a significantly more intense hospital course than those who are HIV-. However, the overall length of hospital stay is not significantly different.

HIV testing among the general US population and persons at increased risk: information from national surveys, 1987-1996.

OBJECTIVES: We used data from national surveys to measure the rate of HIV testing in the general US population and among persons at increased behavioral risk and summarized what has been learned about HIV testing from these surveys. METHODS: Three nationally representative surveys were used: the National Health Interview Survey for 1987 through 1995, the 1995 National Survey of Family Growth, and the 1996 National Household Survey on Drug Abuse. These surveys asked about HIV testing experience and behavioral risks for HIV. Rates of testing were computed for all persons, including those at increased risk for HIV. RESULTS: From 1987 to 1995, the percentage of adults ever tested increased from 16% to 40%. The 3 surveys were consistent with one another, and all showed much higher rates of testing for persons at increased risk for HIV. CONCLUSIONS: Surveys have provided information on HIV testing that is not available elsewhere, including rates of testing from private sources and public programs. Efforts to measure HIV testing and its correlates should continue and should be improved to provide information essential for effective programs.

Tuberculosis beliefs among recent Vietnamese refugees in New York State.

OBJECTIVE: To identify newly arrived Vietnamese refugees' beliefs about tuberculosis (TB) and TB education needs. METHODS: In 1994, the New York State Health Department and the Centers for Disease Control and Prevention conducted a survey of 51 newly arrived adult Vietnamese refugees in two New York counties. After being trained in interview methods, two bilingual researchers asked 32 open-ended questions on the causes of TB, TB treatment, and the disease's impact on work and social relationships. RESULTS: Respondents correctly viewed TB as an infectious lung disease with symptoms such as cough, weakness, and weight loss. Hard manual labor, smoking, alcohol consumption, and poor nutrition were believed to be risk factors. Many respondents incorrectly believed that asymptomatic latent infection is not possible and that infection inevitably leads to disease. Nearly all respondents anticipated that having tuberculosis would adversely impact their work, family, and community activities and relationships. CONCLUSIONS: Targeted patient education is needed to address misconceptions about TB among Vietnamese refugees and to help ensure adherence to prescribed treatment regimens.

Socioeconomic change and patterns of growth in the Andes.

Changes in the pattern of growth over a 20-year period are described for a combined rural and semi-urban population in the District of Nuñoa (Puno) in southern Peruvian Andes. Over the past two decades, Andean regions have experienced many socioeconomic changes, including the implementation of agrarian reform policies and increased integration into a market economy. Local changes in Nuñoa have included improved transportation networks, new markets, an expanded public school system, and improved health care facilities. Secular trends in stature and weight have been found to be associated with social and economic development throughout the developing world, including Peru. The purpose of this paper is to present the findings from a re-study of growth in the Nuñoan population, and to assess whether changing conditions in Nuñoa have resulted in secular increases in growth. A cross-sectional sample of 1,466 children and adults and mixed-longitudinal sample of 404 children (age 3-22), measured between 1983 and 1984, are compared to similar samples collected from the same location between 1964 and 1966. Adolescents are taller, heavier, and somewhat fatter in the present population, although these differences diminish or disappear in adulthood. Age of maturation, peak growth velocities, and cessation of growth may come 1 to 2 years earlier than in the 1960s. As was found in earlier studies, growth velocities are low, the adolescent growth spurt is small, and sexual dimorphism is delayed. No secular trends in adult stature were found. Thus, the effects of social and economic change on nutrition, health, and growth in the population are uneven and generally unclear. This points to inequalities in access to the benefits of change throughout the region.