bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analytical Solution of Transient Multiphase Flow to a Horizontal Well With Multiple Hydraulic Fractures
Authors: Shojaei Hasan , Tajer Ehsan S. 
Published: August 2013

Abstract
This paper presents an analytical model for three-phase flow towards a horizontal well with multi-stage hydraulic fractures, producing from a low-permeability oil reservoir (e.g. shale oil) under primary depletion. The model accounts for time-dependent trilinear-flow model (Brown et al. 2011) and solution-gas drive model (Muskat 1981).
While there are numerous analytical models proposed for inflow of horizontal wells with multistage fractures, they do not consider three-phase flow condition and/or time dependent behavior (i.e. they assume steady or pseudo-steady state conditions). These two conditions should be honored for low-permeability oil reservoirs with prolonged transient period which produce oil, water and dissolved gas.
In this paper, we first present the mathematical framework for the transient three-phase trilinear flow towards a multi-fractured horizontal well in a bounded oil reservoir. Later, we combine the flow equations with the material balance equations to account for pressure depletion and solution-gas drive during primary production. We compare the predictions of our analytical model with a commercial numerical simulator. We demonstrate very good agreements of these two different approaches. Last, the advantages and limitations of this new method are discussed.
Production forecast using the presented analytical model is significantly faster in comparison to the numerical simulator. This finds applications where multiple realizations are required, either during the optimal design of key factors (i.e. number of stages, spacing, optimal fracture conductivity) or during the characterization of hydraulic fractures by matching the production history.
Probabilistic Evaluation of Global Technically Recoverable Tight Gas Resources
Authors: Dong Zhenzhen , Holditch Steve A. , Ayers Walter B. 
Published: August 2013

Abstract
For many countries outside North America, potentially large resources of natural gas in place are present in unconventional reservoirs, such as tight (low-permeability) sandstone/limestone, shales and coal beds. However, there are no reliable estimates of technically recoverable resources (TRR) for these unconventional reservoirs, and many countries lack advanced technology, such as horizontal drilling and hydraulic fracturing, necessary to develop unconventional resources. To encourage investment in these technologies, new resources estimates are needed. The objective of this study was to develop a methodology and software for probabilistic resource estimation, and to use this new technology to estimate global technically recoverable gas resources in tight sands.
Tight gas reservoirs are present in every petroleum province, and global tight gas resources in place are large. However, it is uncertain how much of the in-place resource is technically recoverable. Although some publications report TRR of tight gas for small geographical areas, little is known publicly about these resources on a global scale.
The objective of our work was to determine the probabilistic distribution of TRR of tight gas, worldwide. To achieve this goal, we developed a computer program, Unconventional Gas Resource Assessment System (UGRAS). The program integrates a Monte Carlo technique with an analytical reservoir simulator. This combination provides an excellent means to predict production profiles for a wide variety of reservoir characteristics and producing conditions. Using UGRAS, we established probabilistic distributions of original gas in-place and TRR for selected tight gas formations in the United States and derived a representative distribution of recovery factors for tight gas reservoirs. The recovery factors follow a logistic distribution, with a P50 of 79%.
We extended the distribution of recovery factors gained from our analyses of tight gas reservoirs in the United States to estimate TRR of tight gas worldwide, outside the United States. Global technically recoverable tight gas is estimated to be 38,000 (P10) to 84,000 (P90) Tcf, with a P50 value of 58,000 Tcf. Results of this work support the existence of significant global resources of technically recoverable tight gas and may have potential to guide energy strategy, such as to forecast future energy supply worldwide. UGRAS is a robust tool that may be used to evaluate and rank tight gas resources, worldwide.
Impact of Delays and Shut-Ins on Well Productivity
Authors: Crafton James W. , Noe Sandra L. 
Published: August 2013

Abstract
A population of over 270 wells, including over 80 Marcellus wells, was investigated to assess the impact of various early production management strategies, with attention given to the time delay between stimulation and first production, often referred to as the "resting" or "soak" period and the effect of subsequent shut-ins. Subsets of this population were used to perform the various evaluations. Four significant control factors became apparent. The use of non-volatile interfacial tension management chemistry and the rate of change of the surface flowing pressure significantly impacted the long-term performance of the wells. The use of the IFT chemistry significantly mitigated, but did not prevent, damage arising from delay to first production or shut-ins. Based on the performance metric used, delay to first production is not beneficial. However, based on other data, the probability of improvement with IFT management was less than one in four and without IFT management was about one in eight. Once on production, the rate with which the flowing pressure was decreased had an important impact on the reservoir / wellbore connectivity. If the rate of surface flowing pressure decrease was greater than about 250 psi per day, the loss of connectivity was obvious. The last control factor was the benefit derived from using high conductivity proppants, in conjunction with the IFT management achieved with persistent Interfacial Tension Modifier fluids.
A Correlation to Evaluate the Fracture Permeability Changes as Reservoir is Depleted
Authors: He Jun , Ling Kegang , Pei Peng , Ge Jun , Qin Wenting 
Published: August 2013

Abstract
The increasing development of unconventional resource plays an important role in filling the gap between demand and conventional oil and gas supply. Due to the nature of low permeability, tight gas and shale reservoirs need fractures, natural and artificial, to produce hydrocarbon at commercial rates. Fracture permeability is a key factor affecting the development of these unconventional reservoirs. It is observed that fracture permeabilities decline as reservoirs are depleted because pore pressure declines lead to the closures of fractures and the permeability reductions. Therefore a correlation to quantify the fracture permeabilities varying with pore pressures is highly demanded.
In this study we investigated the effects of pore pressures on fracture permeabilities assuming constant in-situ stresses exert on the formations. Starting from the force balance, we derived equations to calculate fracture permeability based on fracture geometry. Our new correlations can also be used to evaluate the changing fracture permeability during the recovery of hydrocarbon. The proposed correlations provide a way to estimate the fracture permeability at initial pressure and the depleted pressure at any production stage. We noticed that some experiments had been conducted to build relationships between fracture permeability and pressure for some types of rocks. The empirical correlations from experiments are only as good as the databases they based on. Our research provided theoretical correlations and can be applied to any conventional and unconventional reservoirs universally. The proposed methods considered the laminar flow as well as turbulent flow in the fracture, which is often observed in gas well. Under the conditions of no core sample available to test the impact of pressure on fracture permeability, or special core analyses prohibited by cost and time, the proposed correlations are powerful tools to estimate the change of permeability with producing time.
Long Term Forecasting in Shale Reservoirs by Using Rate Transient Analysis
Authors: Gunaydin D. , He Z. , Brown K. G. , Deasy M. A. , Porter M. D. , Corinchock D. J. 
Published: August 2013

Abstract
Shale reservoirs have become one of the most promising natural gas resources in the energy industry. However the complex nature of shale, combined with limited production history, make predicting recovery very difficult in these reservoirs, especially early in the life of the well.
The hyperbolic form of the Arps equation has been modified for use in estimating reserves and forecasting production in shale reservoirs. Although the ease and accessibility of this method make it convenient for most applications, the Arps equation has limitations (assumes boundary-dominated flow, and assumes that flowing bottomhole pressure, drainage area, permeability and skin factor are all constant). By analyzing production data using Rate Transient Analysis (RTA) theory, analytic models can be developed and used to forecast production and recovery in shale gas reservoirs. Because RTA-based models are not subject to many of the assumptions imposed in the development of the Arps equation, these models are much more versatile than decline curves derived using the Arps modified hyperbolic equation.
In this paper, we present a practical workflow for performing RTA to determine the key performance parameters of horizontal shale wells with multiple fractures. This methodology provides a deterministic approach to estimate long term well performance in a shale reservoir. One important advantage over using the Arps equation is the ability to forecast production under different operating strategies. Using this workflow, the production and economic impacts resulting from different completion designs and operational scenarios (e.g., delayed installation of compression) can be studied.
This methodology was implemented on data sets from over 150 Marcellus Shale wells. Forecasts determined using this workflow compare favorably to the forecasts estimated by decline curve analysis and reservoir simulation. Field examples from Marcellus wells are included in this paper to demonstrate the workflow and results.
Understanding the Inter-Relationship of Key Parameters in Unconventional Shale Reservoirs Using Analytical Solutions
Authors: Lalehrokh F. , Jayakumar R. , Lawal H. 
Published: August 2013

Abstract
Gas shales have become an attractive target due to their huge resource of 500 to 780 TCF. Due to the complexity of shale gas reservoirs and their ultra-low nano Darcy permeabilities, they are termed as ‘unconventional’ reservoirs. Contact to a large reservoir surface area is necessary to produce oil or gas at sustainable rates. Improvements in horizontal drilling and massive hydraulic fracturing technology have made economic extraction of these "unconventional" reservoirs feasible.
The scope of this paper is to illustrate methodology for analyzing rate-time and pressure data from horizontal wells with multiple hydraulic transverse fractures. Three distinctive scenarios are considered for a single shale gas well. The implications of multiple interpretations for the same well are discussed in detail. First scenario considers the well in internal linear transient flow with a large stimulated reservoir volume (SRV) and drainage area requirement and the implications that arise with this assumption. The second scenario considers the well is in depletion flow period but this transition has happened later in the life of the well. The third scenario considers the well has gone to an early transition period which implies high reservoir permeability (K) and small effective fracture half-length, i.e., a possibility of contribution from natural fractures in the vicinity of the wellbore. Each scenario has been analyzed in detail to demonstrate an easy step by step approach to understand the implication of multiple interpretations on the overall well performance. This approach will help us understand a common problem that is mostly overlooked which is the reservoir contribution outside the SRV - external reservoir volume (XRV).
The outcome of each of the mentioned scenarios is distinctive. Therefore choosing the right scenario for the well is very critical. In order to wisely choose the correct scenario, a combination of various parameters such as: XRV size, current well flow regime, the time that well has gone to depletion, available drainage area, presence of natural fractures and matrix permeability must be considered. In this paper, the impact of the aforementioned parameters on well performance analysis, reservoir assessment and field development is analyzed in-depth.
An Examination of Infill and Offset Drilling Patterns on Field Development for Shale Wells
Authors: Sahai Vivek , Jackson Greg , Lalehrokh Farshad , Rai Rakesh 
Published: August 2013

Abstract
Capital expenditures, personal and equipment resources, acreage lease restrictions, and market conditions strongly influence drilling and development plans for shale resources. Delaying the start of new wells is understood to reduce the NPV of a section but variations in the arrangement of infill wells in a section have not been thoroughly examined to date.
In this paper, the impact of timing and pattern of well placement on NPV, and recovery factor at an optimal number of wells per section is studied. The sensitivities included wells with a small amount of stimulated reservoir volume (SRV) overlap. To study the drilling/infill pattern, three limiting scenarios were evaluated, i.e. an infill scheme where future wells are drilled between existing wells, a linear scheme where future wells are immediate offsets of existing wells, and a hybrid scheme that is a combination of the infill and linear schemes. Four different start times of future wells were evaluated to determine impact of timing.
The results show EUR is relatively insensitive to the drilling schedule. The section recovery factor can be conserved as long as all the wells are drilled in a reasonable amount of time. A quantification of the NPV reduction as a result of the order and scheduling of wells is presented. These results illustrate once a threshold of total cumulative production from a section is achieved, infill wells may not be economic and thus should be carefully considered.
The results of the study are a resource to aid operators in understanding the impact of well spacing as shale plays mature from being in the appraisal phase to the field development phase. Knowledge of how development decisions impact optimal resource development will allow operators to adapt their drilling plans to maximize their return on investment.
Experimental and Numerical Studies on the Micro-fractures and its Significance Toward Production of Shales: A Case Study
Authors: Wei Chenji , Wang Yuhe , Qin Guan , Li Qianyao , Killough John 
Published: August 2013

Abstract
The mechanisms of shale gas storage and flow are complex. Understanding the microstructure is an important step for evaluating a new shale gas play toward accurate reserve estimation and recovery prediction. The emphasis of this paper is study on the micro-fractures observed on the research shale formation.
The approaches involved in this study include experimental study and numerical modeling. Longmaxi Shale, which is an emerging Lower Silurian marine shale gas play in China with huge potential according to preliminary explorations, is the research formation in this paper. Core samples used in the experiment are collected from the target layer of Longmaxi Shale. The pore structure is visualized in nano-scale using Scanning Electron Microscope (SEM). In order to evaluate the influence of micro-fracture, a micro-model is built to explicitly simulate the micro-factures. The effect of micro-fracture on gas drainage capacity of shale matrix is then scaled up to a well model using a triple porosity approach.
SEM images reveal well-developed micro-fractures on the Longmaxi Shale. Micro-fractures exhibit strong heterogeneity. The width, length and connectivity of the micro-fractures vary notably. This feature is believed can significantly influent the gas drainage capacity of shale matrix and as a result well performance. Sensitivity analysis is conducted by varying micro-fracture density, width, length and connectivity. Results show that micro-fracture plays an important role in production performance. This is because that the well-developed micro-fractures enhance the gas drainage capacity of shale matrix. Thus, micro-fractures observed in Longmaxi Shale have to be considered in evaluating potentials of this new shale gas play.
This study characterizes the microstructure of Longmaxi Shale and discusses the significance of micro-fractures, which provides important information to support engineers and geologist for better understanding the marine shale and optimizing production plan on the marine shale.
How Natural Fractures Could Affect Hydraulic-Fracture Geometry
Authors: Taleghani Arash Dahi , Olson Jon E. 
Published: August 2013

SummaryHydraulic fracturing is recognized as the main stimulating technique to enhance recovery in tight fissured reservoirs. These fracturing treatments are often mapped by use of hypocenters of induced microseismic events. In some cases, the microseismic mapping shows asymmetry of the induced-fracture geometry with respect to the injection well. In addition, the conventional theories predict fracture propagation along a path normal to the least compressive in-situ stresses, whereas in some cases the microseismic data suggest fracture propagation parallel to the minimum compressive stress. In this paper, we present an extended-finite-element-method (XFEM) model that can simulate asymmetric fracture-wing development as well as diversion of the fracture path along natural fractures. Simulation results demonstrate the sensitivity of the fracture-pattern geometry to differential stress and natural-fracture orientation with respect to the in-situ maximum compressive stress. We examine the properties of sealed natural fractures that are common in formations such as the Barnett shale and show that they may still serve as weak paths for hydraulic-fracture beginning and/or diversion. The presented model predicts faster fracture propagation in formations where natural fractures are favorably aligned with the tectonic stresses.
The Effect of Audit Committee Industry Expertise on Monitoring the Financial Reporting Process
Authors: Cohen Jeffrey R. , Hoitash Udi , Krishnamoorthy Ganesh , Wright Arnold M. 
Published: August 2013

ABSTRACT
Calls from practice suggest that audit committee members with industry expertise can improve audit committee effectiveness. Nevertheless, regulators and the extant literature have focused on the financial expertise of the audit committee. We posit that audit committee industry knowledge is valuable because accounting guidance, estimates, and oversight of the external auditor are often linked to a company's operations within a particular industry. Taking a holistic view, we examine two measures of financial reporting quality (financial restatements and discretionary accruals) and two measures of external auditor oversight (audit and nonaudit fees). As predicted, we find that audit committee members who are both accounting and industry experts perform better than those with only accounting expertise. We also find that in certain instances, supervisory experts who are also industry experts perform better than supervisory experts alone. Overall, these results suggest that industry expertise, when combined with accounting expertise, can improve the effectiveness of the audit committee in monitoring the financial reporting process.
Data Availability: All data are gathered from publicly available sources.
Real Activities Manipulation and Auditors' Client-Retention Decisions
Authors: Kim Yongtae , Park Myung Seok 
Published: August 2013

ABSTRACT
In this study, we examine the effect of clients' real activities manipulation (RAM) on auditors' client-retention decisions. We find that, with the exception of RAM through overproduction, clients' opportunistic operating decisions are positively associated with the likelihood of auditor resignations. We also provide evidence that auditors are especially sensitive to clients' RAM to just meet or beat earnings benchmarks in their client-retention decisions. In addition, we find that clients whose auditors resign from engagements tend to hire smaller auditors and these clients engage in RAM more aggressively. Our additional analysis shows that, with the exception of RAM through overproduction, clients' abnormal operating decisions are significantly associated with litigation risk against auditors. Overall, our evidence suggests that auditors drop clients with aggressive RAM to avoid excessive risk.
Data Availability: Data used in this study are available from public sources identified in the study.
Real-Time Support of Pediatric Diabetes Self-Care by a Transport Team
Authors: Franklin Brandi E. , Crisler S. Crile , Shappley Rebekah , Armour Meri M. , McCommon Dana T. , Ferry Robert J. 
Published: August 2013

OBJECTIVE
The study seeks to improve access for underserved patients via novel integration of Pedi-Flite (a critical care transport team) and to validate whether this safely enhances diabetes care and effectively expands the endocrine workforce.

RESEARCH DESIGN AND METHODS
The study retrospectively analyzed pager service use in a cohort of established diabetic patients (n = 979) after inception of Pedi-Flite support. Outcomes included incidence and severity of recurrent diabetic ketoacidosis (DKA) and cost savings generated from reduced referrals to the emergency department (ED) and on-call endocrinologist. We generated descriptive statistics to characterize the study population and ED visits for DKA and constructed logistic regression models to examine associations of pager use and likelihood of ED visitation and nonelective inpatient admission from an ED for DKA.

RESULTS
Pager users comprised 30% of the patient population. They were younger but had more established diabetes than nonusers. While pager users were 2.75 times more likely than nonusers to visit the ED for DKA (P &lt; 0.0001), their visits were less likely to lead to inpatient admissions (odds ratio 0.58; P &lt; 0.02). More than half (n = 587) of all calls to the pager were resolved without need for further referral. Estimates suggest that 439 ED visits and 115 admissions were avoided at a potential cost savings exceeding 760,000 USD.

CONCLUSIONS
Integration of a transport service provides a novel, cost-effective approach to reduce disparities in diabetes care. Advantages include scalability, applicability to other disease areas and settings, and low added costs. These findings enrich an emerging evidence base for telephonic care-management models supported by allied health personnel.