Three Dimensional Thermo-poroelastic Modeling of Fluid Injection and Induced Microseismicity in Naturally Fractured Reservoirs

Interests in naturally fractured reservoirs have grown rapidly in recent years due to the increasing energy needs. Understanding the behavior of naturally fractured reservoirs would be beneficial for a variety of engineering applications, including enhanced oil recovery in the petroleum industry, reservoir stimulation in enhanced geothermal systems, salt water disposal, carbon dioxide storage, and nuclear waste management. In naturally fractured reservoirs with low permeability rock matrix, natural fractures provide primary pathways for fluid flow and dominate the flow behavior of the fractured medium. Fractures are stress sensitive. They could dilate, slip in shear, and propagate possibly as a result of stress changes caused by fluid injection operations, thereby increasing fracture aperture and permeability, and influencing reservoir performance. Injection into fractured reservoirs could also induce seismicity, which is often attributed to shear slippage on fractures. In this study, we developed a three dimensional fully coupled thermo-poroelastic model which is integrated with a stochastic natural fracture network to simulate the response of fractured reservoirs to fluid injection. Fluid injection induces significant perturbations in the pore pressure, temperature and stress fields within a reservoir, and involves coupling between fluid flow, heat transfer, and mechanical deformation. This coupling process is modeled using a linear theory of thermo-poroelasticity and solved using a finite element method. The presence of natural fractures is taken into consideration by implementing a fracture network model into the coupled thermo-poroelastic model. A discrete fracture network is generated based on stochastic descriptions of fracture distribution parameters, including fracture density, size and orientation. The available fracture geometry includes penny-shaped circular fractures, elliptical fractures and rectangular fractures. Since the calculations of flow in non-circular fractures require additional mathematical treatments (Long et al. 1985) and the available solutions to heat transfer in the non-circular fractures are also limited, therefore, the commonly used penny-shaped circular fracture is modeled in this work. The permeability of the fractured rock is estimated using an equivalent permeability approach. The fracture permeability can increase by shear dilation and fracture propagation. For numerical simulations of fracture slip, two most widely used friction models are incorporated, including a constant friction model and a rate-and-state friction (RSF) model that considers the dependence of friction on the slip velocity and the past sliding history. The coupled FEM is solved for pressure, temperature, and deformation in the equivalent continuum medium formed by the fractures and the rock matrix. Knowing the flows and heads within the fracture network and the intersections between fractures, local pressure distribution on individual fracture planes is solved analytically based on an image theory (Rahman et al. 2002). Heat transfer within the interconnected fracture network is modeled by a flow pipe network model considering both the convection via fracture flow and the conduction between adjacent rock mass and the fluid in the fracture. Stress dependent fracture deformation behavior including opening, shear dilation, and possible propagation is considered, and the associated changes in fracture aperture and fracture network geometry are updated for permeability in the coupled FEM. The potential of microseismicity induced by fracture shear slippage is also modeled. The developed model is verified against analytical solutions and previously published numerical results. This model is first used to simulate cold water injection into a naturally fractured reservoir to examine its capability of analyzing the dynamic reservoir response during injection. Results show that the fluid and heat flow within the fractured reservoir are primarily dominated by the connected fracture network. The results also indicate that the overall reservoir permeability enhancement can be attributed to the combined effects of fracture opening, shear slippage, and propagation. A sensitivity study is carried out for investigating the effect of various parameters on the reservoir performance and on the occurrence of induced seismicity during injection. The results show that the injection response of a naturally fractured reservoir is a complex process controlled by multiple factors, including the properties of fracture network, in-situ stress conditions, rock matrix permeability, the properties of injecting fluid, injection scheme and injection temperature. The developed model has a wide variety of engineering applications in naturally fractured rock. Two application examples are present in this dissertation. The first application example is the simulation of reservoir stimulation in the Newberry EGS Demonstration. Field data on the fracture network and in-situ stress and laboratory data on rock and fracture properties are used in model construction. The simulated injection profile, the evolution of permeability and induced microseismic events have good agreements with field observations. Simulation results also show the perturbation and rotation of the in-situ stress field adjacent to the injection well, which helps to explain the discrepancy between the stress models derived pre-injection and inverted from seismic data post-injection. The second application example is a large scale simulation of the 12 years long term wastewater injection in central Oklahoma. A conceptual model is built based on the available data on the fault geometry, regional stress fields, and well injection history. Simulation results show that during injection, the elevated pore pressure can migrate downward from the Arbuckle injection layer into the deeper crystalline basement via the fault system. For nearly critical fractures, a small elevated pressure is sufficient to cause shear slippage of fractures along the optimally oriented Meeker-Prague fault and potentially induce seismicity. Injection strategies of capping the total injected volume, reducing the injection rate, and restricting the injection depth are proposed to reduce the size of the potentially induced seismicity. The numerical model developed in this study is shown to have the capability of analyzing the dynamic reservoir response during fluid injection. It is useful for the design and evaluation of injection plans in naturally fractured reservoirs

Alesco and Mark Resources: Cross-Border Tax Arbitrage, Economic Reality, and Anti-Avoidance Rules in New Zealand and Canada

This essay compares the role given to the concept of economic reality in New Zealand and Canadian cross-border tax arbitrage decisions, particularly Alesco and Mark Resources. Alesco and Mark Resources both address the problem of drawing the line between acceptable tax mitigation and unacceptable avoidance, and adopt economic substance as a key indicator of where this line lies. This essay considers how the concept of economic reality pervades these cases and evaluates the influence of legislative and judicial context to the significance afforded to the concept of economic reality in the two decisions, as well as reviewing how the economic realities jurisprudence has evolved following these cases

Economic evaluations of guideline-based care for chronic wounds: a systematic review

Objectives: The aim of this study was to review all published economic evaluations of guideline-based care for chronic wounds and to assess how useful these studies are for decision making in health services. Methods: Embase, PubMed, Scopus, Health Technology Assessment (HTA) and National Health Service Economic Evaluation Database (NHS EED) were searched on April 16th, 2018. We included studies that evaluated the economic impact and health outcomes associated with implementing evidence-based guidelines as a bundle of care for the prevention and/or treatment of chronic wounds. Information was extracted from each eligible study and organized by the type of chronic wound. The quality of published economic evaluation studies was assessed using the Consolidated Health Economic Evaluation Reporting Standards (CHEERS). Results: A total of 24 economic evaluation studies met the inclusion criteria, of which 12 applied decision analytic models. The compliance with the CHEERS checklist ranged between 43 and 83%. Limitations: We may have missed some economic evaluation studies despite the use of broad search terms. The quality assessment was conducted based on judgment. Using the CHEERS checklist may reflect the way evaluations were reported rather than conducted. Conclusions and Implications of Key Findings: We found that guideline-based care may be cost-saving or cost-effective in most circumstances. The quality and usefulness of reviewed studies for decision making were variable. Better information and higher-quality economic evaluations will increase decision makers’ confidence to promote guideline-based care

Two Sample Tests for High Dimensional Covariance Matrices

We propose two tests for the equality of covariance matrices between two high-dimensional populations. One test is on the whole variance-covariance matrices, and the other is on offdiagonal sub-matrices which define the covariance between two non-overlapping segments of the high-dimensional random vectors. The tests are applicable (i) when the data dimension is much larger than the sample sizes, namely the “large p, small n” situations and (ii) without assuming parametric distributions for the two populations. These two aspects surpass the capability of the conventional likelihood ratio test. The proposed tests can be used to test on covariances associated with gene ontology terms

Cost-effectiveness analysis of an innovative model of care for chronic wounds patients

Current provision of services for the care of chronic wounds in Australia is disjointed and costly. There is large variability in the way that services are provided, and little evidence regarding the cost-effectiveness of a specialist model of care for treatment and management. A decision-analytic model to evaluate the cost-effectiveness of a specialist wound care clinic as compared to usual care for chronic wounds is presented. We use retrospective and prospective data from a cohort of patients as well as information from administrative databases and published literature. Our results show specialist wound clinics are cost-effective for the management of chronic wounds. On average, specialist clinics were $3,947 cheaper than usual clinics and resulted in a quality adjusted life year gain of 0.04 per patient, per year. Specialist clinics were the best option under multiple scenarios including a different cost perspective and when the cost of a hospital admission was reduced. Current models of care are inefficient and represent low value care, and specialist wound clinics represent a good investment compared to current approaches for the management of chronic wounds in Australia

Economic evaluation of an intervention designed to reduce bullying in Australian schools

Background There is a shortage of information on the costs and benefits of anti-bullying programs implemented in Australia. Information on the costs and benefits of anti-bullying programs is vital to assist policy making regarding the adoption of these programs. The aim of this study was to estimate the changes to costs and health benefits of implementing the “Friendly Schools Friendly Families” (FSFF) anti-bullying intervention in Australia. Methods A societal perspective cost-effectiveness analysis was undertaken based on randomised controlled trial data for an anti-bullying intervention implemented in primary schools in Western Australia. The modelling strategy addressed changes to costs comprising intervention costs, less cost-savings, and then changes to health benefits measured by avoidable disability-adjusted life years (DALYs). Costs and health benefits were identified, measured, and valued in 2016 Australian dollars. Intermediate events modelled included anxiety disorders, depressive disorders, intentional self-harm, cost-savings accrued by educator time, and reduced productivity losses for carers associated with absenteeism. Uncertainty analysis and scenario analyses were also conducted. Results The prevalence of bullying victimisation was reduced by 18% by the Friendly Schools Friendly Families anti-bullying intervention. At a national level, this is expected to result in the avoidance of 9114 DALYs (95% CI 8770–9459) and cost-savings of A$120 million per year. The majority of cost-savings were associated with the reduction in mental healthcare. The model results demonstrated that the FSFF anti-bullying intervention is likely to be a cost-effective approach to reduce bullying in Australia, relative to a threshold of A$50,000 per DALY averted, with an ICER of A$1646. Conclusions The Friendly Schools Friendly Families anti-bullying intervention represents a good investment compared to usual activities for the management of child and adolescent bullying in Australia. The investment and implementation of evidence-based interventions that reduce bullying victimisation and bullying perpetration in schools could reduce the economic burden associated with common mental health disorders and thereby improve the health of many Australians

Diabetes-related foot disease in Australia: a systematic review of the prevalence and incidence of risk factors, disease and amputation in Australian populations

Background Diabetes-related foot disease (DFD) is a leading cause of global hospitalisation, amputation and disability burdens; yet, the epidemiology of the DFD burden is unclear in Australia. We aimed to systematically review the literature reporting the prevalence and incidence of risk factors for DFD (e.g. neuropathy, peripheral artery disease), of DFD (ulcers and infection), and of diabetes-related amputation (total, minor and major amputation) in Australian populations. Methods We systematically searched PubMed and EMBASE databases for peer-reviewed articles published until December 31, 2019. We used search strings combining key terms for prevalence or incidence, DFD or amputation, and Australia. Search results were independently screened for eligibility by two investigators. Publications that reported prevalence or incidence of outcomes of interest in geographically defined Australian populations were eligible for inclusion. Included studies were independently assessed for methodological quality and key data were extracted by two investigators. Results Twenty publications met eligibility and were included. There was high heterogeneity for populations investigated and methods used to identify outcomes. We found within diabetes populations, the prevalence of risk factors ranged from 10.0–58.8%, of DFD from 1.2–1.5%, and the incidence of diabetes-related amputation ranged from 5.2–7.2 per 1000 person-years. Additionally, the incidence of DFD-related hospitalisation ranged from 5.2–36.6 per 1000 person-years within diabetes populations. Furthermore, within inpatients with diabetes, we found the prevalence of risk factors ranged from 35.3–43.3%, DFD from 7.0–15.1% and amputation during hospitalisation from 1.4–5.8%. Conclusions Our review suggests a similar risk factor prevalence, low but uncertain DFD prevalence, and high DFD-related hospitalisation and amputation incidence in Australia compared to international populations. These findings may suggest that a low proportion of people with risk factors develop DFD, however, it is also possible that there is an underestimation of DFD prevalence in Australia in the few limited studies, given the high incidence of hospitalisation and amputation because of DFD. Either way, studies of nationally representative populations using valid outcome measures are needed to verify these DFD-related findings and interpretations

Factors associated with healing of diabetes-related foot ulcers: observations from a large prospective real-world cohort

Factors associated with healing of diabetes-related foot ulcers: observations from a large prospective real-world cohor

Using measures of quality of care to assess equity in health care funding for primary care: analysis of Indonesian household data.

BACKGROUND: Many countries implementing pro-poor reforms to expand subsidized health care, especially for the poor, recognize that high-quality healthcare, and not just access alone, is necessary to meet the Sustainable Development Goals. As the poor are more likely to use low quality health services, measures to improve access to health care need to emphasise quality as the cornerstone to achieving equity goals. Current methods to evaluate health systems financing equity fail to take into account measures of quality. This paper aims to provide a worked example of how to adapt a popular quantitative approach, Benefit Incidence Analysis (BIA), to incorporate a quality weighting into the computation of public subsidies for health care. METHODS: We used a dataset consisting of a sample of households surveyed in 10 provinces of Indonesia in early-2018. In parallel, a survey of public health facilities was conducted in the same geographical areas, and information about health facility infrastructure and basic equipment was collected. In each facility, an index of service readiness was computed as a measure of quality. Individuals who reported visiting a primary health care facility in the month before the interview were matched to their chosen facility. Standard BIA and an extended BIA that adjusts for service quality were conducted. RESULTS: Quality scores were relatively high across all facilities, with an average of 82%. Scores for basic equipment were highest, with an average score of 99% compared to essential medicines with an average score of 60%. Our findings from the quality-weighted BIA show that the distribution of subsidies for public primary health care facilities became less 'pro-poor' while private clinics became more 'pro-rich' after accounting for quality of care. Overall the distribution of subsidies became significantly pro-rich (CI = 0.037). CONCLUSIONS: Routine collection of quality indicators that can be linked to individuals is needed to enable a comprehensive understanding of individuals' pathways of care. From a policy perspective, accounting for quality of care in health financing assessment is crucial in a context where quality of care is a nationwide issue. In such a context, any health financing performance assessment is likely to be biased if quality is not accounted for

Equity of health financing in Indonesia: A 5-year financing incidence analysis (2015-2019).

BACKGROUND: In 2014, Indonesia launched a single payer national health insurance scheme with the aim of covering the entire population by 2024. The objective of this paper is to assess the equity with which contributions to the health financing system were distributed in Indonesia over 2015 - 2019. METHODS: This study is a secondary analysis of nationally representative data from the National Socioeconomic Survey of Indonesia (2015 - 2019). The relative progressivity of each health financing source and overall health financing was determined using a summary score, the Kakwani index. FINDINGS: Around a third of health financing was sourced from out-of-pocket (OOP) payments each year, with direct taxes, indirect taxes and social health insurance (SHI) each taking up 15 - 20%. Direct taxes and OOP payments were progressive sources of health financing, and indirect tax payments regressive, for all of 2015 - 2019. SHI contributions were regressive except in 2017 and 2018. The overall health financing system was progressive from 2015 to 2018, but this declined year by year and became mildly regressive in 2019. INTERPRETATION: The declining progressivity of the overall health financing system between 2015 - 2019 suggests that Indonesia still has a way to go in developing a fair and equitable health financing system that ensures the poor are financially protected. FUNDING: This study is supported through the Health Systems Research Initiative in the UK, and is jointly funded by the Department of International Development, the Economic and Social Research Council, the Medical Research Council and the Wellcome Trust