bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proppant Distribution Observations from 20,000+ Perforation Erosion Measurements
Authors: Roberts Glyn , Whittaker Jeff , McDonald Joe , Paxson Tanner 
Published: January 2020

Abstract
Recent step changes in downhole video technology and image analysis have coincided with a growing understanding of how perforation erosion can be used to measure the effectiveness of limited entry hydraulic fracturing. This has led to rapid growth in video-based perforation imaging and produced a substantial database of measured and statistically analysed perforations. A review of recurring patterns and common trends identified in the database provides useful insights on proppant placement and distribution.
An analysis was undertaken on a dataset that includes detailed individual perforation dimensions from more than 6,000 clusters and 600 stages. With a focus on understanding the uniformity of proppant distribution, the initial phase was to identify significant recurring patterns in cluster level proppant placement derived from perforation erosion measurements. Multiple treatment design parameters were then analysed to understand their influence on proppant distribution. Among those considered were stage length, number and spacing of clusters per stage, the number of perforations shot per cluster, perforation charge type and phasing.
While every well produces a unique set of results, several recurring trends were identified across the database. These often indicated sub-optimal proppant placement with undesirable consequences for production and ultimate recovery. Results demonstrate thatProppant placement is often significantly non-uniform across a stageA strong tendency for greater heel-side perforation erosion is typically observed for ‘geometric’ stage and cluster designsA similar strong preference for proppant to be placed in perforations located towards the low-side of the wellbore is also apparentMore uniform proppant distribution can be obtained using an engineered design approachAlthough they are often inter-related several treatment parameters can be engineered with relative ease to produce more uniform proppant placement
Analysis methods, results, treatment parameter considerations, primary conclusions and other relevant findings will be discussed in detail.
The majority of research on treatment design parameters that influence proppant placement has mainly used CFD-DEM models. The approach presented in this paper, however has used empirical, in-situ data. The size of the dataset and the frequency at which certain tendencies are observed provide some confidence that the approach and results are valid and can help improve treatment design. It is hoped that the results of the study will provide hydraulic fracture specialists with further evidence-based guidelines that ultimately help increase production and enhance ultimate recovery.
A New Mechanism for the Formation of Hydraulic Fracture Swarms
Authors: Manchanda Ripudaman , Shrivastava Kaustubh , Zheng Shuang , Sharma Mukul 
Published: January 2020

Abstract
Mine-back experiments, lab experiments, and cores taken through fractured rock show that hydraulic fracturing treatments can create swarms of fractures. Subcritical crack growth, microcracking ahead of the fracture tip and failure of weak planes in the rock are mechanisms that have helped explain fracture swarming observed in both natural and hydraulic fractures. In this work, we show that fracture swarms can also form in homogeneous rocks by complex stress fields induced in the reservoir by propagating hydraulic fractures or by other geologic events.
A 3-D fracturing simulator based on the Displacement Discontinuity Method (DDM) and a 3-D fracturing-reservoir simulator based on the Finite Volume Method (FVM) were used to simulate hydraulic fracture propagation. These models can accurately account for stress shadow effects and simulate fracture turning during propagation with the direction of propagation calculated using the maximum tangential stress criterion. Simultaneous propagation of multiple fractures is simulated to exhibit multi-stranded fracture propagation behavior in the absence of natural fractures in the reservoir. Additionally, we assess the impact of natural fractures in the reservoir on the created fracture swarms.
The stress shadow around a single fracture is spatially variable. Simulation of the propagation of multiple fractures shows that parts of the fractures propagating in lower stress contrast regions turn more readily than the parts of the fractures propagating in higher stress contrast regions. The smaller width of the fracture in the high-stress layers induces a smaller stress shadow while the larger width of the fracture surface in the low-stress layers induces a larger stress shadow. Higher stress interference in certain layers causes fracture turning in those layers and induces splitting of the fracture tip resulting in swarms of fractures. The FVM simulations clearly show this effect. Fracture branching and tip splitting are only evident when these simulations are run in 3-D. The fracture branching results obtained from the simulators show good agreement with field core-through observations from the Eagle Ford and the Permian basins. This work shows that the stress field created by propagating fractures can result in the creation of fracture swarms. It is shown that this branching can happen in the absence of material flaws and weaknesses. This new mechanism of fracture branching to create fracture swarms is quantified through both DDM and finite volume simulations.
Developing Methodology for DFIT Design and Pressure Interpretation by Coupled Reservoir Geomechanics Flow Simulation
Authors: Mohamed Mohamed , Thaker Tirth , Ibrahim Mazher , Ozkan Erdal 
Published: January 2020

Abstract
A numerical, coupled reservoir flow and geomechanics model has been built using a black-oil simulator and evaluated for diagnostic fracture injection test (DFITs) in unconventional reservoirs. DFITs have evolved into a commonly used technique to generate direct estimates of some key unconventional reservoir characteristics. Challenges, however, arise due to the complexity of the unconventional reservoir characteristics, long shut-in times to reach the closure pressure, and the long test durations to obtain realistic reservoir parameters from pseudoradial flow. One way to improve the analysis of minifrac tests in unconventional reservoirs is to use a coupled geomechanics and flow simulator, which is capable of representing the interactions between the reservoir fractures and minifrac developed during minifrac tests.
The numerical model used in this work is based on coupling the geomechanical rock properties with the reservoir flow model. The geomechanical model simulates the growth and subsequent closure of the hydraulic and secondary fractures by modeling the change in the reservoir stresses. Furthermore, the model simulates the minifrac pressure response before fracture-closure as well as during the after-closure falloff period. The pressure response during the falloff period is then analyzed to evaluate the reservoir properties using Nolte pre-closure and after-closure analysis techniques.
The coupled geomechanics and flow simulation of minifrac provides the capability of modeling the fracture breakdown and fracture closure and estimating the fracture dimensions. The traditional fracture design tools provide similar information focusing only on the geomechanics of the rock and ignoring the effect of the reservoir flow. An additional advantage of the simulator used in this work is to provide estimates of fracture stiffness, fracture closure permeability, residual permeability, and permeability of the matrix.
The simulator allows pressure matching and successfully simulates the reservoir flow for extended shut-in periods. The simulator allows designing DFITs with different injection volumes, rates, and shut-in periods and thus helps provide the optimum parameters for the test. The after-shut-in flow regimes generated by the simulation model agree with the DFIT theory.
A Rapid Injection Flow-Back Test RIFT to Estimate In-Situ Stress and Pore Pressure in a Single Test
Authors: Wang HanYi , Sharma Mukul 
Published: January 2020

Abstract
Quantifying in-situ stress and pore pressure has significant applications in earth sciences and subsurface engineering, such as fault zone studies, underground CO2 sequestration, oil and gas reservoir development, injection into deep wells, and geothermal energy exploitation. The extended leak-off test (XLOT)/ pump-in and flow-back test (PIFB) have been the industry-standard for stress determination during drilling for some time, where drilling mud is injected to create a small fracture in an vertical open-hole below a newly cemented casing. This is followed by a shut-in phase and/or flow-back phase. However, there is still no consensus as regards to which methods should be used to pick closure stress from XLOT/PIFB data, and the influence of drilling mud and near wellbore hoop stress can further complicate the interpretation process. In addition, the risks of formation damage and wellbore integrity issues are also major concerns when executing XLOT/PIFB during high-cost drilling operations.
Diagnostic Fracture Injection Tests (DFIT) is another standard method for estimating in-situ stress and other important reservoir/fracture parameters such as pore pressure and permeability. Such tests can be executed in either open-hole or cased-hole, and even carried out in horizontal wells. In very low permeability reservoirs, it may take several days for fracture closure and weeks to observe the after-closure flow regime. The required shut-in time for DFITs can be extremely long in unconventional reservoirs (weeks or months). In some circumstances, if the reservoir is naturally fractured and its effective permeability is strongly pressure-sensitive during the before-closure period, picking the closure stress in the DFIT data becomes ambiguous.
In this study, we present a new approach to estimate in-situ stress and pore pressure using a Rapid Injection Flow-Back Test (RIFT) in low permeability formations, where the fracture closure process is facilitated via controlled flow-back that is followed by a shut-in period. This significantly shortens the time required to conduct a test that allows us to estimate the in-situ stress and the pore pressure. The time-convolution solution for RIFT is derived by preserving the physics of unsteady-state reservoir flow, elastic fracture mechanics, material balance, and progressive fracture closure. Our new approach not only provides an unambiguous way to estimate in-situ stress (even in naturally fractured formations), but also allows us to estimate pore pressure with data from a test that lasts only a few hours. It also provides to estimate effective fracture volume. Both numerical simulations and field cases are presented to demonstrate the advantages of RFIT, along with a discussion of cautions and the potential pitfalls when designing and executing RIFT.
Distributed Acoustic and Temperature Sensing Applications for Hydraulic Fracture Diagnostics
Authors: Li Xinyang , Zhang Jimmy , Grubert Marcel , Laing Carson , Chavarria Andres , Cole Steve , Oukaci Yassine 
Published: January 2020

Abstract
Hydraulic fracturing operations in unconventional reservoirs are increasingly being monitored with fiber-optic (FO) Distributed Acoustic and Temperature Sensing (DAS/DTS). In this paper, we discuss how a single well equipped with fiber optics and DAS can be used as a diagnostic tool to better understand the completions program of three offset wells and the fiber instrumented well.
Strain measurements were initially conducted for seismic studies, then followed by measurements of fluid injections from monitoring wells to better understand placement along the lateral section of the wellbore for programs such as hydraulic fracturing, water flooding, and steam injection. The broadband DAS signals have shown of value for the monitoring of microseismic, as well as thermal and mechanical strain of the fiber over the entire well-pad's completion process. During well stimulation, as a fracture propagates to an offset wellbore with fiber deployed, the DAS measurements can be used to monitor very small changes of strain on the fiber. Analysis of the Cross-Well Communication (CWC) strain measurements provide information about possible fracture numbers and locations, as well as the fracture propagating rate based on known well distance. Changes in the strain measurements are coupled with microseismic events that can be simultaneously monitored using the same interrogator unit and fiber optic cable.
Here we present various diagnostic tools for DAS that help to better understand the completions program. A variety of physical effects, such as temperature, strain and micro seismicity are measured and correlated with the treatment program to aid in the analysis. Two of the offset wells were zipper-fractured first, then the fiber installed well was zipper-fractured with the third offset well. By monitoring CWC strain measurements we show that DAS can assess the treatment and performance of neighboring wells that are not instrumented with fiber optic cable. Low frequency strain events from neighboring wells provide direct measurements of the fracture density and possible fracture network post fiber well completion. CWC measurements can provide strain levels that can be analyzed in the context of the various completion parameters including stage length, clusters, and well spacing, etc. We also discuss the fluid and proppant allocations measurements that can be performed on the well with fiber installation. We show how DAS can be used as a tool for investigating cluster efficiency, diverter effectiveness, and for determining completions problems like screen-outs and stage communication.
The analysis of the DAS data demonstrates that current fiber-optic technology can provide enough sensitivity to detect a significant number of frac events that can be used for an improved reservoir description and as an assessment of the completions program.
Mixing Equations in Various Geometries
Authors: Brigham William E. 
Published: January 2020

ABSTRACT
Often, in flow through porous media, the mixing characteristics of the flowing fluids are defined by the diffusivity equation. Solutions of this equation are available for linear flow and close approximations are available for radial flow. In this paper, one of the radial flow approximation methods has been generalized to a variety of geometries. The solution is assumed to be in the form of an error function; and equations are derived for the standard deviation, i.e., the argument of the error function. By breaking the flow system into segments and by repeated use of these solutions, mixing can be calculated in a large variety of flow systems. For example, equations can be used to calculate tracer flow behavior in reservoirs and mixing in vertical miscible displacement.

INTRODUCTION
In the absence of viscous fingering, the equations defining mixing in a linear miscible displacement are well known.
Association between peripheral blood/bronchoalveolar lavage eosinophilia and significant oxygen requirements in patients with acute eosinophilic pneumonia
Authors: Choi Joon Young , Lim Jeong Uk , Jeong Ho Jung , Lee Ji Eun , Rhee Chin Kook 
Published: January 2020

Abstract
Background We investigated the association between a combination of two markers, peripheral (PEC) and bronchoalveolar lavage (BAL) eosinophil percentage (BEP), and oxygen requirements in patients with acute eosinophilic pneumonia (AEP). Methods We retrospectively reviewed the medical records of patients with AEP treated at the Armed Forces Capital Hospital between May 2012 and May 2017. We used correlation analyses to assess the association between PEC/BEP and clinical outcomes in AEP patients. Receiver operating characteristic (ROC) curve analyses were used to calculate the cut-off value for BEP that categorised patients requiring a significant oxygen supply. The BAL/blood eosinophil (BBE) score was introduced to stratify patients with peripheral eosinophilia and elevated BEP. Clinical characteristics and outcomes were compared between the different groups. Multiple logistic regression was performed for significant oxygen requirements using two different models using age, C-reactive protein (CRP), smoking duration, and BBE score (model 1) and age, CRP, BEP, and PEC (model 2). Results Among the 338 patients, 99.7% were male, and their mean age was 20.4 ± 1.4 years. Only 0.6% of patients were never smokers and the mean number of smoking days was 26.2 ± 25.4. Correlation analyses revealed that both the PaO2/FiO2 ratio and duration of oxygen supply were associated with BEP. ROC curve analyses indicated a cut-off level of 41.5%. Patients with a high BBE score had favourable outcomes in terms of hypoxemia, hospital days, intensive care unit admission, oxygen supply days, and steroid treatment days. Multiple logistic regression revealed that BEP and BBE score tended to be associated with significant oxygen requirements. Conclusions In this study, we revealed that both peripheral and BAL eosinophilia is associated with favourable outcomes in AEP patients.
Case Identification of Mental Health and Related Problems in Children and Young People using the New Zealand Integrated Data Infrastructure
Authors: Bowden Nicholas , Gibb Sheree , Thabrew Hiran , Kokaua Jesse , Audas Richard , Merry Sally , Taylor Barry , Hetrick Sarah 
Published: January 2020

Abstract
Background In a novel endeavour we aimed to develop a clinically relevant case identification method for use in research about the mental health of children and young people in New Zealand using the Integrated Data Infrastructure (IDI). The IDI is a linked individual-level database containing New Zealand government and survey microdata. Methods We drew on diagnostic and pharmaceutical information contained within five secondary care service use and medication dispensing datasets to identify probable cases of mental health and related problems. A systematic classification and refinement of codes, including restrictions by age, was undertaken to assign cases into 13 different mental health problem categories. This process was carried out by a panel of eight specialists covering a diverse range of mental health disciplines (a clinical psychologist, four child and adolescent psychiatrists and three academic researchers in child and adolescent mental health). The case identification method was applied to the New Zealand youth estimated resident population for the 2014/15 fiscal year. Results Over 82,000 unique individuals aged 0-24 with at least one specified mental health or related problem were identified using the case identification method for the 2014/15 fiscal year. The most prevalent mental health problem subgroups were emotional problems (31,266 individuals), substance problems (16,314), and disruptive behaviours (13,758). Overall, the pharmaceutical collection was the largest source of case identification data (59,862). Conclusion This study demonstrates the value of utilising IDI data for mental health research, moving beyond incidence rates based on single data sources, and providing directions for future use and validation, including further linkage of data to the IDI.
Usage of Cloud Storage Facilities by Medical students in a low-middle income country, Sri Lanka: A cross sectional study
Authors: Hettige Samankumara , Dasanayaka Eshani , Ediriweera Dileepa Senajith 
Published: January 2020

Abstract
Background:
Cloud storage facilities (CSF) has become popular among the internet users. There is limited data on CSF usage among university students in low middle-income countries including Sri Lanka. In this study we present the CSF usage among medical students at the Faculty of Medicine, University of Kelaniya.
Methods:
We undertook a cross sectional study at the Faculty of Medicine, University of Kelaniya, Sri Lanka. Stratified random sampling was used to recruit students representing all the batches. A self-administrated questionnaire was given.
Results:
Of 261 (90.9%) respondents, 181 (69.3%) were females. CSF awareness was 56.5% (95%CI: 50.3% - 62.6%) and CSF usage was 50.8% (95%CI: 44.4 - 57.2%). Awareness was higher in males (P=0.003) and was low in senior students. Of CSF aware students, 85% knew about Google Drive and 70.6% used it. 73.6% and 42.1% knew about Dropbox and OneDrive. 50.0% and 22.0% used them respectively. There was no association between CSF awareness and pre-university entrance or undergraduate examination performance. Inadequate knowledge, time, accessibility, security and privacy concerns limited CSF usage. 69.8% indicated that they would like to undergo training on CSF as an effective tool for education.
Conclusion:
CSF awareness and usage among the students were 56.5% and 50.8%. Google drive is the most popular CSF. Lack of knowledge, accessibility, concerns on security and privacy limited CSF usage among students. Majority were interested to undergo training on CSF and undergraduate Information Communication Technology (ICT) curricula should introduce CSF as effective educational tools.
Implementation of a new program of gestational diabetes screening and management in Morocco: A qualitative exploration of health workers’ perceptions
Authors: Utz Bettina , Assarag Bouchra , Lekhal Touria , Damme Wim Van , De Brouwere Vincent 
Published: January 2020

Abstract
Background: Gestational diabetes mellitus (GDM) is associated with an increased risk for a future type 2 diabetes mellitus in women and their children. As linkage between maternal health and non-communicable diseases, antenatal care plays a key role in the primary and secondary prevention of GDM associated adverse outcomes. While implementing a locally adapted GDM screening and management approach through antenatal care services at the primary level of care, we assessed its acceptability by the implementing health care providers. Methods : As part of a larger implementation effectiveness study assessing a decentralized gestational diabetes screening and management approach in the prefecture of Marrakech and the rural district of Al Haouz in Morocco, we conducted four focus group discussions with 29 primary health care providers and seven in-depth interviews with national and regional key informants. After transcription of data, we thematically analysed the data using a combined deductive and inductive approach. Results: The intervention of screening and managing women with gestational diabetes added value to existing antenatal care services but presented an additional workload for first line health care providers. An existing lack of knowledge about gestational diabetes in the community and among private health care physicians required of public providers to spend more time on counselling women. Nurses had to adapt recommendation on diet to the socio-economic context of patients. Despite the additional task, especially nurses and midwives felt motivated by their gained capacity to detect and manage gestational diabetes, and to take decisions on treatment and follow-up. Conclusions : Detection and initial management of gestational diabetes is an acceptable strategy to extend the antenatal care service offer in Morocco and to facilitate service access for affected pregnant women. Despite its additional workload, gestational diabetes management can contribute to the professional motivation of primary level health care providers.