bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydraulic Fracture Design in the Presence of Highly-Stressed Layers: A Case Study of Stress Interference in a Multi-Horizontal Well Pad
Authors: Ueda Kenji , Kuroda Shintaro , Rodriguez-Herrera Adrian , Garcia-Teijeiro Xavier , Bearinger Doug , Virues Claudio J. , Tokunaga Hiroyuki , Makimura Dai , Lehmann Jurgen , Petr Christopher , Tsusaka Kimikazu , Shimamoto Tatsuo
Published: January 2018

A design of hydraulic fracturing in variably-stressed zones is one of key components for an effective multi-zone, multi-horizontal well pad treatment. In the recent literature, optimum completion strategies catering for stimulation-induced in-situ stress changes are discussed, however, only few of these focus on vertical stress changes and its impact on multi-zone fracture geometries. In this paper, we present an approach to design contained hydraulic fractures in a high stress layers by studying the role of vertical stress shadowing on actual field data.

In modeling hydraulic fractures with pseudo-3D models, if fracture simulations are initiated in high stress zones, "artificially" unbounded height growth results in very limited lateral propagation. On the other hand, 3D hydraulic fracturing models are too computationally expensive to optimize large design jobs, for example, in multi-horizontal well pads. In this paper, we employ a Stacked Height Growth Model, whereby fractures are also discretized vertically yet retain the numerical formulation pseudo-3D models. Coupling with finite element stress solvers then allows to identify vertical stress changes in the vicinity of induced hydraulic fractures and to understand the interference between hydraulic fracture sequences and their respective microseismic signatures.

Considering a potential combination of fracturing sequences, it was revealed that stress perturbations from the neighboring well hydraulic fractures initiating from low stress layers can be used to increase stress within the same zone and also potentially reduce stresses in higher-stress layers above and below. By modeling and calibrating an actual multi-zone, multi-horizontal stimulation job, we elaborate on the benefits of increasing stress barriers before fracturing in higher-stress layer to avoid the chances of re-fracturing from high stress zones. Regarding hydraulic fracture geometries, we explain our results by analyzing actual microseismic observations with respect to simulated stress patterns after stimulation. We explore the notion of deliberately ordering hydraulic fracture to manage vertical interference and create more contained fractures in a multi-zone horizontal well pad.

Fracturing in a higher-stress zone will naturally divert the energy into low stress, potentially unproductive zones. In an effort to manage this phenomenon, this paper presents one of the few data-rich case studies on multi-zone, multi-well engineered stimulation design. The approach shown in this paper can be a helpful reference to understand fracture height growth in the presence of both vertical and horizontal stress shadowing.
Applying Subsurface DNA Diagnostics and Data Science in the Delaware Basin
Authors: Silva J. , Ursell L. , Percak-Dennett E.
Published: January 2018

The application of DNA sequencing in the oil industry provides a non-invasive, economical, and high-resolution data source for elucidating hydrocarbon fluid movement. DNA Diagnostics could be used to understand drainage height and inform the vertical spacing of wells, as well as provide the ability to derive/predict depositional environments based on biomarker signatures.

To date, DNA sequencing has been applied in over 200 wells across 8 basins in North America, including the Permian, Eagle Ford, and Bakken. Subsurface DNA Diagnostics are used to guide well spacing, evaluate well interference (e.g. frac hits), determine oil potential, and understand production profiling.

The effective application of DNA sequencing in the oilfield requires the use of advanced data science techniques and machine learning. To date, the industry's application of machine learning has been focused on production and completion parameters that provide a statistical view of the subsurface. In oilfield DNA sequencing, millions of data points per well are generated; and to apply these direct measurements to the subsurface requires novel machine learning techniques which are presented here.

In this analysis, we present the results of DNA sequencing from a 33-well study in the Delaware Basin. Well cuttings and produced fluid samples were obtained in a non-invasive manner to generate stratigraphically unique signals for hydrocarbon fluid movement. Various data science techniques are presented to interpret the data with initial observations providing a novel view into production across formations.

Additionally, we will provide an overview of future work and how we plan to augment the dataset with other more conventional techniques in order to fine-tune the uncertainties associated with a new data source and methodology.
Effectiveness of Geometric Versus Variable Shot Clusters to Stimulate a Percolating Crack Network Capable of Sustaining Flow
Authors: Ardakani E. P. , Baig A. M. , Urbancic T. I. , Kahn D. , Rich J. , Langton D. , Silver K.
Published: January 2018

The perforation strategy for a hydraulic fracture completion for an unconventional reservoir can have a very large influence on the overall success of the injection program at effectively stimulating that network. To evaluate differences in perf clustering methodologies, operators are frequently in need of observational evidence to suggest which strategy is most efficient. We present a paper where we look at a detailed analysis of microseismicity for different stages with different completion programs.

While event distributions tend to be the first and most frequently examined aspect of a microseismic monitoring effort, because the generation of a microseismic event is not immediately diagnostic of fluid-induced fracturing, the event clouds tend to overestimate the effective area of fracturing. In order to gain further insight into how microseismic events describe effective fracture growth, a deeper look at the waveforms through techniques like Seismic Moment Tensor Inversion (SMTI) and subsequent stress inversion can be effective. These steps are necessary to describe the discrete network of cracks, from the microseismic data. Using a fracture network topology approach, the network can then be characterized in terms of its ability to percolate fluids.

We compare how cracks behave for a regular geometric shot cluster (GSC) and a variable shot cluster (VSC) and assess variations in the stimulations. Both shot clusters were completed in consecutive stages of the same lateral. The mechanisms from the GSC stages show shear-dominant mechanisms with opening and closing components in roughly equal proportions, while the VSC stages have a higher concentration of shear-tensile opening failures. Furthermore, the GSC stages showed modest connectivity around the treatment well relative to the VSC stages, which showed significant growth of connected fractures away from the treatment well. Since the VSC stages also showed relatively more stable stress behaviour than the GSC stages, these observations suggest that stability in stresses allows for steady growth of the fracture network across the reservoir.

This type of higher-order analysis of microseismic data is critical to establishing value from this data stream in terms of completion evaluation. The recognition that each microseismic event is tied to the rupture of a crack in the reservoir allows for these types of comparisons to be made in a robust fashion and be tied to the underlying geomechanics that governs the type of response from one type of completion to the other.
Parent-Child Fracture Interference: Explanation and Mitigation of Child Well Underperformance
Authors: Manchanda Ripudaman , Bhardwaj Prateek , Hwang Jongsoo , Sharma Mukul M.
Published: January 2018

In the last few years, several operators in unconventional plays have seen fracture interference between existing production wells (parent wells) and newly fractured infill wells (child wells). This interference usually has a negative impact on the production from both the parent and child wells. In this work, a mechanistic explanation of the parent-child interaction is provided using results from poro-elastic simulations. Child well underperformance is studied in detail and mitigation strategies are discussed. Results shown in this work quantify the impact of depletion and refracturing on child well fracturing.

In this work, a 3D reservoir-scale poro-elastic geomechanics software (Multi-Frac) was used to model the depletion of the parent well region and calculate its impact on pressure, total stress and effective stress. Refracturing simulations of the parent well were conducted to showcase the importance of a good refracturing operation in reducing the probability of fracture hits from the child well to the parent well. The poro-elastic capabilities of Multi-Frac help in analyzing the stress changes in the reservoir induced by depletion and re-fracturing. These stress changes explain the observed fracture hits from child wells.

The stress changes and the depletion patterns also explain the underperformance of the child well fractures. Implications of depletion on both total stress and effective stress are analyzed. Decrease in the total stress near the parent well creates a zone of attraction for the child well fracture, thus, causing the child well fracture to be created in a region of extensive depletion. Depletion induced increase in the effective stress was observed from the simulation. This increase in the effective stress makes fracture network creation harder and thus reduces the productivity of the child well fractures. Re-fracturing of the parent well showed an increase in the stress in the reservoir and can help avoid fracture hits from neighboring child wells. Thus, re-fracturing a parent well and subsequently fracturing a child well can be a possible strategy to mitigate the impact of fracture hits and thereby improve the EUR of the pad.

The three main factors that induce interference between parent wells and child wells are reservoir depletion, reservoir total stress changes and reservoir effective stress changes. All of these factors have been studied and quantified in this work. Modifications to parent well fracturing treatment design, refracturing treatment design and child well fracturing treatment design are suggested to improve productivity.
Hydraulic Fracture Interaction with Cemented Natural Fracture: A Three Dimensional Discrete Element Method Analysis
Authors: Lee Hunjoo P. , Razavi Omid , Olson Jon E.
Published: January 2018

The propagation path of hydraulic fracture is significantly affected by the properties of cemented natural fractures (i.e., veins), such as, stiffness, tensile and shear strength, and flow characteristics. Moreover, the magnitude of stress anisotropy can control the results of hydraulic fracture crossing or diverting into the vein. To study the effect of vein properties and the differential stress on the interaction of hydraulic fractures with mineral-filled veins, we employed a three-dimensional (3D) Discrete Element Method (DEM) model which couples the fluid flow and the bonded-particle assembly. The hydraulic fracture interaction with the vein was investigated by monitoring the bond breakages and measuring the fracture diversion distance along the vein before kinking back into the rock matrix. Numerical results are in good agreement with the fracture diversion results from the published experimental and numerical SCB tests of Marcellus shale with calcite-filled veins. The propagating hydraulic fracture is more likely to divert into the veins with smaller approach angle. Increasing the differential stress leads to fracture crossing than diversion into the vein. For veins with greater stiffness than the host rock, microcracks were generated in the vein before the hydraulic fracture intersected it. For tight formations with stiffer veins, the vein permeability did not have much influence on the fracture diversion result since the damage induced by the stress concentration ahead of the hydraulic fracture tip dominated the fluid flow in the vein.
Frac Hit Induced Production Losses: Evaluating Root Causes, Damage Location, Possible Prevention Methods and Success of Remediation Treatments, Part II
Authors: Rainbolt Michael F. , Esco Jacey
Published: January 2018

Millions of dollars in production losses are occurring from fracture-driven well-to-well interference (frac hits) in horizontal wells in unconventional play reservoirs. The work presented in SPE 187192 has been continued in this paper with a new case study (Case Study V), data from a pair of Wolfcamp B wells in the Permian Basin. The parent well suffered fracture interference during the child well's stimulation operations, negatively effecting production. The child and parent wells were both completed with the "plug and perf" technique. The parent well was completed with 74 stages while the child well's completion consisted of 105 frac stages. The child well was drilled with a longer lateral and the first 72 stages of the well's fracturing operations caused clear, repeatable pressure changes in the parent well. The data from these two wells is rich in cause and effect and permits compelling observations and conclusions. These findings were then compared to those from Case Studies I-IV, SPE 187192.

Detailed plots of the pressure changes superimposed with fracturing data were created and studied to better understand the significance and cause of what was happening to the Case Study V parent well. The shut-in pressure data from the parent well was taken at the intake of the electrical submersible pump (ESP) and recorded in 1-3 minute increments. Both wells have the same number of perf clusters per stage, stage spacing and amount of sand per stage. One-second fracture stimulation data for both completions was available. Case Study V plots and examples from Case Studies I-IV were put side-to-side and back-to-back to quickly view the similarities and differences. Fact-based conclusions were reached regarding causality of fracture-driven communication and interference between these wells.

Preface

The study for this paper is based on and uses data from nearly 200 individual fracture stimulation stages pumped in five pairs of wells. In order to document and discuss that much information, there are numerous plots and illustrations. While this is perhaps unconventional, it must be pointed out that a paper that is focused on data MUST show the data. Time constraints prevented the inclusion of several additional plots and "Part III" is being planned and is in the works. SPE 187192 (part I), King et al (2017) will be referred to several times and a few of the old plots are shown. There are new plots and observations from Case Studies I-IV.
Benefits of Engineering Fracture Design. Lessons Learned from Underperformers in the Midland Basin.
Authors: Parsegov S. G. , Niu G. , Schechter D. S. , Laprea-Bigott M.
Published: January 2018

Hydraulic fracturing (HF) is a very complex engineering process. It involves rock and fluid mechanics, mixed mode rock failure and transportation of individual proppant particles. This process is multiscale both in time and spatial domains that is why it is almost impossible to create a fully coupled 3D model with a detailed description of physical and chemical processes even with significant assumptions.

Recent data indicates well completion becomes more expensive than the drilling itself for several unconventional reservoirs. The reason is an increase of fluid and proppant pumped at high rates. Thus, the critical importance of engineering optimization of fracture spacing and individual pumping schedule for maximization of Net Present Value (NPV), Estimated Ultimate Recovery (EUR), and other metrics in the "lower for longer" price environment.

Unfortunately, unconventional operators see little value in fracture modeling because of its complexity and amount of data required for any reasonable predictive power. That is why many companies consider geometric design as the cheapest and hence the most efficient option thus resulting in trial and error to optimize HF design.

In this paper we use publicly available well logs and completion data covering the Midland Basin from the University Lands website. We also demonstrate that HF model calibration with microseismic data and stochastically generated Discrete Fracture Network (DFN), although is a challenging task, may improve our understanding of fracture design pitfalls and to become an essential step for optimum engineering design. Insights from our work can be useful to increase the predictive power of in-house models and reduce total cost and effort involved in this complex modeling.
Active Well Defense in the Bakken: Case Study of a Ten-Well Frac Defense Project, McKenzie County, ND
Authors: Bommer Peter A. , Bayne Marcus A.
Published: January 2018

The effects of well interference between existing producing wells and newly stimulated wells (commonly known as "frac hits") are of growing concern as full-density development accelerates across all the North American shale plays. Strategies to mitigate the negative effects of such interference are becoming increasingly important as frac hits become more frequent.

This case study presents a second-generation active well defense project involving four new wells and six offsetting legacy wells in the Bakken and Three Forks formations located in the North Fork Field, McKenzie County, ND. The operator has experienced numerous examples of stimulation interference in this field as its development operations have progressed into the full-density phase. Stimulation interference is defined as any increase in pressure occurring in a well as a result of stimulation activities in an offset or nearby well. While such interference has not necessarily had a lasting effect on legacy production, it has in some cases resulted in the need for costly remediation due to the migration of solids into the legacy laterals. The well defense efforts described herein are intended to minimize the need for post-stimulation remediation in legacy wells by preventing solids migration.
Mechanisms for the Formation of Complex Fracture Networks in Naturally Fractured Rocks
Authors: Shrivastava Kaustubh , Sharma Mukul M.
Published: January 2018

Complex fracture networks are formed when hydraulic fractures grow in naturally fractured reservoirs. Current planar fracture models are inadequate for capturing the effect of natural fractures on fracture propagation and addressing the important question of optimum fracture spacing and well spacing. Stress interference due to three-dimensional fracture networks can result in intricate fracture geometries, which are usually neglected by fracture models. In this paper, we present a three-dimensional hydraulic fracturing simulator that models the deformation and stress fields induced by both the dilation and shear failure of all existing and propagating hydraulic or natural fractures. It is shown that the simulator allows us to capture the complex fracture geometries, and microseismic signatures often observed in heterogeneous and naturally fractured rocks.

Fracture geomechanics is modeled in a computationally efficient manner using a fully three-dimensional displacement discontinuity method. The simulator captures the physics of fracture growth, fracture turning, fluid distribution in fracture networks, and the intersection of hydraulic fractures with pre-existing natural fractures. The model captures the interaction between multiple branches of a hydraulic fracture (stress shadow effect). The model also simulates the shear failure of hydraulically disconnected natural fractures to simulate microseismic activity and can account for the effect of shear failure and slippage along bed boundaries and along natural fractures on hydraulic fracture propagation.

The effect of pre-existing natural fracture density and orientation on the geometry of the fracture network generated is systematically studied. It is shown that natural fractures play an important role in determining the propagation direction of hydraulic fractures and this effect is quantified. At high natural fracture density, the propagation direction of a hydraulic fracture is dominated by the orientation of natural fractures rather than the far field stress magnitude and direction. The density of the natural fractures also affects the complexity of the final created fracture geometry.
An Engineered Approach to Hydraulically Fracture the Vaca Muerta Shale
Authors: Buijs Hernán , Ponce Jorge
Published: January 2018

In recent years, several papers have been published on the subject of rock properties, stress and permeability models in the Vaca Muerta unconventional formation, with the intention of understanding fractured well performance. In most cases, however, these publications have failed on providing sufficient information to adequately describe the generated models, nor have studied in detail the benefits and limitations of applying different schools of thought and incorporating field measurements during the design and evaluation of hydraulic fractures. This work seeks to explain a systematic approach to characterize, constrain and validate such models through integration of prefrac diagnostic injections, core data, independently-determined fracture dimensions, and postfrac production data. The final objective is to build predictive models that can be used to improve completion strategies in this promising but still immature play.
Optimization of Bakken Well Completions in a Multivariate World
Authors: Scanlan W. P. , Pierskalla K. J. , Sobernheim D. W. , Christian J. , Dutta R. , Sharma A. , Seigel S. , Zhang B. , Boykin B.
Published: January 2018

The advent of mega-sized hydraulic fracturing jobs which incorporate increased proppant per foot density, enlarged fluid volumes, tighter cluster spacing, and shorter stages in the Bakken/Three Forks play, have led to significantly higher IP's on the order of 20% over the past two years. Yet despite this dramatic increase, concerns exist as to whether treatments are fully optimized with respect to costs of overall volumes, rates, and concentrations. This paper describes two case histories, one in the Middle Bakken and one in the Three Forks formations of the Williston Basin, where a multidisciplinary geoscience and engineering team was assembled to attempt to answer the optimization question within the confines of real-world operational logistics and cost constraints.

In these case histories, an optimization process is described that begins with wellbore context. The consideration of offset wells in the area, data analytics processes considering reservoir quality, and perceived successful completions for the area are incorporated as input. Detailed layered and geomechanical models are then constructed using drilling, neural network and public domain data to produce optimized perforation cluster design and grouping in precise fracturing stages. A rigorous planar 3D hydraulic fracturing model is used to simulate fracture geometry characteristics including height growth, half length, and aperture. Lastly, proppant tracing and production modeling were used to validate the approach used.

The result of the project was to develop an optimization process incorporating the multidisciplinary technical team's expertise to provide an integrated, cost-effective completion design that would lead to more rigorous support for why these engineering decisions were taken. In addition, a secondary goal was to leverage software and database capacity for completion decisions into a "best practices process" that would neither burden the existing E&P staff nor hinder the completion timing. The resultant case study captures the process, technology analysis, weighted benefits, takeaway learnings, and results from two such wells within the Williston Basin.
A Summary of the US Environmental Protection Agency's Multiyear Study of the Potential Impacts of Hydraulic Fracturing on Drinking Water Resources
Authors: Dunn-Norman S. , Hufford W. , Almond S. W. , Consulting S. Almond
Published: January 2018

In December 2016, the United States Environmental Protection Agency (U.S. EPA) published the findings of their multiyear study entitled, "Hydraulic Fracturing for Oil and Gas: Impacts from the Hydraulic Fracturing Water Cycle on Drinking Water Resources in the United States." EPA's final report (with contributing studies) totals over a thousand pages, and sparked controversy during the assessment, after the release of their draft 2015 report and the final document. This paper provides a summary of the EPA study effort and processes, and highlights key finding and limitations of the work.

In 2010 Congress authorized the U.S. EPA to study the potential impact of hydraulic fracturing (HF) on water quality. EPA's office of Research and Development (ORD) drafted a study approach that included (1) defining research questions and identifying data gaps, (2) conducting a process for stakeholder input and research prioritization, (3) developing a detailed study design that would lead to external peer-review, and (4) implementation of the planned research. This study approach was reviewed by a committee formulated under the EPA's Scientific Advisory Board (SAB), and one author of this paper served on the first SAB review panel. A separate SAB committee was empaneled later to review the results of the research and draft conclusions. All three authors of this paper were appointed to the second SAB panel.

Initially, industry considered the Congressional request to be a focused assessment related to the actual process of HF on drinking water. It later became clear that the interpretation by the EPA of the Congressional request was a broader evaluation on the "life cycle" of water during the drilling and completion activities for oil and gas development. The final focused study approach was based on a HF hydraulic fracturing water cycle beginning with water acquisition, chemical mixing, and injection of the treatment. After HF (the actual hydraulic fracturing treatment, also known as "completion"), the fracture water cycle includes produced water handling, HF water disposal and reuse, and identification and hazard evaluation of chemicals across the hydraulic fracturing water cycle. Each of the stages in the HF process are treated separately in the study, and includes fundamental explanations, scientific research, academic (literature) review, and stakeholder input.

This paper provides a succinct summary of the EPA HF study. The summary is important for industry, government and academia as the final Assessment report is currently being cited as a basis for policy and regulatory development worldwide.
Production Performance of Infill Horizontal Wells vs. Pre-Existing Wells in the Major US Unconventional Basins
Authors: Lindsay G. , Miller G. , Xu T. , Shan D. , Baihly J.
Published: January 2018

In most US unconventional basins, operators often start development by drilling the minimum number of wells needed to hold their acreage. These initial wells are sometimes called "parent" wells. Operators then start drilling their infill development wells, which many operators are currently in the process of doing across various unconventional basins. Infill performance can be highly variable, with operators making great efforts to ensure infill wells perform comparable to or better than existing parent wells. This challenge will become more magnified in the unconventional industry as infill development surpasses parent well drilling. To add more uncertainty, limited research exists showing basin-wide trends as to how infill wells can be expected to perform on average in comparison to their parent well counterparts. We studied infill well performance in numerous US basins, with the objectives of understanding performance trends and their causes, along with providing recommendations for maximizing infill well potential.

We evaluated the performance of newly drilled infill wells compared to their parent wells, which had been produced for some time. With publicly available production and well information, an evaluation was performed for the following major unconventional basins: Bakken/Three Forks, Barnett, Bone Springs, Eagle Ford, Fayetteville, Haynesville, Marcellus, Niobrara, Wolfcamp (Midland and Delaware Basins), and Woodford.

Using a spatial, statistical approach with key production indicators, we identified key trends across the various basins where the infill wells produced at different production rates compared to their parent wells. Overall, there is about a 50% chance that a child well will outperform a parent well; However, normalizing production to total proppant pumped and lateral length suggests that larger volumes with longer laterals in infill wells may be needed to achieve similar rates to the parent wells.

Underperformance of infill wells may likely be because of existing depletion and inter-well production competition with both parent and other infill wells. Additionally, in areas where significant depletion is expected, predicting the performance of new infill wells can be very difficult. This paper will discuss alternative methodologies and technologies that may help understand and increase the production potential of lower performing infill wells.
Diagnostic Testing and Analysis of Hydraulically Fractured Dual-Porosity Formations
Authors: Elwaziry Y. , Soliman M. Y.
Published: January 2018

Several techniques were developed to analyze the after-closure fracture data of a DFIT/MiniFrac test. The majority of these techniques assume the reservoir is homogeneous. However, this assumption is not always satisfied: a formation may be heterogeneous and naturally fractured, making the published techniques not applicable in this case.

A most recent technique developed by Soliman et al. (2010) presented an analytical solution for an injection-falloff test for a naturally fractured formation. The solution was found to be effective, especially in the analysis of MiniFrac tests. However, the solution was applicable only in the absence of residual fracture conductivity.

A solution for an injection-falloff test for a naturally fractured and hydraulically fractured formation has been developed. The solution was established by inference using numerical simulation. MiniFrac tests are simulated and analyzed for naturally and hydraulically fractured formations. The study includes infinitely conductive fractures, finite conductivity fractures and radial flow regime.

Furthermore, the developed solution was employed successfully to analyze field data of a shale formation that is known to be naturally fractured. A naturally fractured formation that was hydraulically fractured is examined and presented.
Wavelet Analysis of Fracturing Pressure Data
Authors: Unal E. , Siddiqui F. , Soliman M. Y.
Published: January 2018

This study demonstrates a successful application of Wavelet Analysis to fracturing pressure data across various conventional and unconventional formations to evaluate post treatment data and enhance future stimulation practices. This methodology was compared to the proven Moving Reference Point (MRP) technique developed by Pirayesh et al (2013), to improve the understanding of wavelet analysis. As a fracturing diagnostic tool, the wavelet analysis technique can also be used as companion diagnostic tool alongside previously published methods (such as MRP etc.)

Wavelet analysis of a signal is the mathematical decomposition of that signal into orthogonal wavelet components. The level of decomposition is chosen to discern high and low-resolution parts of the signal. The process represents the signal as a sum of translations and scalings of the chosen wavelet to obtain coefficients of each wavelet.

Fracturing treatment pressure signals occur at various frequencies with finite durations that makes it possible to divide the pressure signals into many components and analyze them individually by wavelet transformation. Discrete Wavelet Transformation by Daubechie wavelets was implemented on fracture propagation pressure to various resolution levels to reveal necessary information within the data. The detail coefficients were analyzed by examining the anomalies at various resolution levels.

Wavelet analysis was performed on various shale and conventional fracturing data. Some interesting patterns are readily discernable from the wavelet detail coefficients. For instance, during the injection of proppants, there is an amplitude change in the detail coefficients at the exact moment when the proppant contacts the formation surface. This is expected because wavelet analysis is sensitive to any discontinuity in the system. Furthermore, such amplitude changes are also observed in the analyzed pressure data corresponding to tip screen-out and near wellbore sand-out events. Comparing such events along-side the MRP method paves the way for early detection of screen-out events. A comparison with the MRP technique is also provided in this study. This method reduces the uncertainty in analysis of Nolte-Smith and MRP method by providing an independent estimate of fracture propagation characteristics.

There have been publications discussing wavelet transformations of various formation and reservoir parameters (permeability, reservoir pressure, etc.), and discussing the application of wavelets for noise reduction and data smoothing. However, this is the first study mainly about wavelet analysis of fracture injection pressure data to understand and detect anomalies during various completion treatments. Ultimately, this technique helps to improve treatment designs and efficiency by analyzing fracture and formation behavior of the treatment and enhance decision making during execution, by providing early screen-out detections.
Measurements While Fracturing: Nonintrusive Method of Hydraulic Fracturing Monitoring
Authors: Parkhonyuk S. , Fedorov A. , Kabannik A. , Korkin R. , Nikolaev M. , Tsygulev I.
Published: January 2018

A new method of nonintrusive fracturing process monitoring in real time has been developed. The method is a combination of advanced signal processing algorithms and a tube wave velocity model based on Bayesian statistics and, thus, does not require complex hardware. This enables cost-effective and timely decisions at the wellsite. The technique was validated in the field in several fracturing and refracturing jobs.
Choosing the Right Products
Authors: Boothe M. , Videlock S. , Lincicome D. , Greaves R. , Hyden R. , Olson K. E.
Published: January 2018

The Right Products Program is designed to drive the assessment of all chemical products used in hydraulic fracturing through an effective decision-making process aimed at minimizing the toxicity of fracture fluids. This program increases the accountability of our chemical suppliers, improves HS&E stewardship, and reduces our overall impact potential from a human health and environmental standpoint. The Right Products Program provides an internal workflow through which all chemicals are reviewed to ensure that the safest and most appropriate products are used. In addition, the Right Products Program provides standards that chemical suppliers must meet prior to the product's use in operations.

This program demonstrates the commitment of Southwestern Energy (SWN) to do the right thing in order to responsibly develop our resources. The Right Products Program provides the ability to evaluate products company-wide through a consistent review process made possible by corporate, interdisciplinary, and operational collaboration.

This paper provides details behind the methodology of the Right Products Program. We will discuss the hazard assessment and product scoring, workflow, lessons learned, and provide examples of assessed products.
Visual Analysis on the Effects of Fracture-Surface Characteristics and Rock Type on Proppant Transport in Vertical Fractures
Authors: Huang Hai , Babadagli Tayfun , Andy Li Huazhou , Develi Kayhan
Published: January 2018

The fracture-surface characteristics (such as roughness and fractal dimensions) may greatly affect the proppant transport during hydraulic fracturing operation. Few researches have focused on investigating the proppant transport in vertical fracture with actual surface characteristics. As a continuation of our previous study (Huang et al. 2017), we qualitatively investigatethe migration of proppants in rough and vertical fractures by considering the effects of surface characteristics and rock type on the instantaneous transport and areal spreading of proppant in the fractures. We fractured different types of tight rocks (including limestone, marble, tight sandstone, and granite) with Brazilian test and molded them to manufacture 20×20cm transparent replicas with an aperture of 1 mm. We characterized the surface characteristics of these rock samples with different fractal dimensions. Subsequently, dyed fracturing fluid with or without proppant loading was injected into the rough vertical fracture. In each test, we monitored the inlet pressure continuously while the proppants were being transported in the fracture. The process was videotaped to monitor the proppant distribution in the rough fracture. Different from our previous study (Huang et al. 2017), a higher injection rate is used in this present study. The experimental results obtained in this study further consolidate the many findings reported in our recent study (Huang et al. 2017): in rough and narrow fracture, the surface roughness plays a pivotal role in affecting how proppants settle in the fracture as well as where the proppants settle in the fracture. Roughness of the vertical fractures tends to significantly enhance the vertical placement of proppants in the fracture, leading to a much higher proppant-filling ratio in a rough fracture than in a smooth fracture. Interestingly, in addition to the bridging effect observed in Huang et al. (2017), a previously formed proppants cluster can be broken up under a higher-rate slurry flow. The bridging of proppants and its subsequent breaking up can recursively occur during the high-rate slurry flow, resulting in fluctuations in the proppant filling ratios as well as fluctuations in the pressure profiles recorded in the inlet of the fracture model. The roughness of fracture models not only affects how much area of the fracture is being occupied by the proppants in the fracture, but also affects how tightly the proppants are filling up the fracture. Different types of rock have different surface characteristics, leading to the observed differences with regard to how the proppants migrate, settle down and fill up the fractures. No definite correlation could be established between any of the fractal numbers and the relative coverage of proppants in the fracture. More experiments, however, need to be conducted to reach more concrete conclusions in this regard.
Flowback-Based Minimum Stress Estimate in Low-Permeability Environment: Procedure, Interpretation, and Application in the Vaca Muerta Shale
Authors: Pichon Stephane , Varela Raul , Manière Jérôme , Hasbani Jose , d'Huteau Emmanuel
Published: January 2018

Low-permeability formations must be hydraulically fractured to produce at commercial rates. A good understanding of the formation stress conditions is critical for completion design, but requires in-situ measurement as calibration to support the geomechanical evaluation. This calibration is commonly done using diagnostic formation injection test (DFIT) methodology by creating a hydraulic fracture and then waiting for it to close through leakoff to the formation. However, in a low-permeability low-leakoff environment, application of this approach might become limited because of the time to fracture closure and the non-uniqueness of the interpretation. This paper demonstrates the applicability of the fracture flowback method to define closure pressure. Although proposed in the 1980s, this method has been underused by the industry. One of the objectives of this paper is, therefore, to advocate through field examples its simplicity of development, interpretation, and repeatability, particularly in low-leakoff reservoirs such organic shale formations.

The procedure is composed of a sequence of various cycles of pump-in flowback through a fixed choke, pressure rebound, and fracture reopening. The proposed methodology offers several minimum stress measurements for repeatability and quality check purposes, reduces interpretation non-uniqueness, and can be completed within 1 hour, making it compatible with the hydraulic fracturing operations.

Test design considerations, such as well geometry, pump rate, fluid volume, choke size, or perforation requirements, are reviewed to maximize the chance of success. Interpretation of the different possible patterns that can be observed is discussed and illustrated with practical examples from the Vaca Muerta shale. Comparison is made between the pump-in flowback and calibration decline approaches performed over the same interval. Repeatability is evaluated, and discrepancies between cycles are investigated.

A direct application of the method is the calibration of a stress profile when applied to a vertical well. However, additional observations related to the fracture closure mechanism or residual fracture conductivity can be drawn by detailing the flowed-back volumes or rate of rebound pressure. These observations can be related to the lithology when the procedure is implemented in different intervals of the same formation.
New API Standards for Shale Development
Authors: Benge Glen , Miller David , Miller Stephanie , Goodman Roland
Published: January 2018

The American Petroleum Institute (API) is the only national trade association representing all facets of the oil and natural gas industry whose mission is to promote safety across the industry globally and to influence public policy in support of a strong, viable U.S. oil and natural gas industry. For almost 100 years, API has led the development of petroleum and petrochemical equipment and operating standards. These represent the industry's collective wisdom on everything from drill bits to environmental protection and embrace proven, sound engineering and operating practices and safe, interchangeable equipment and materials.

In support of increased use of hydraulic fracturing, new editions of API's hydraulic fracturing standards have been developed to provide the latest technical direction for operators working to continuously improve well integrity, groundwater protection, and environmental safety. API's standards for shale development have worked alongside robust state regulations to ensure safe and responsible energy development with hydraulic fracturing for over 65 years.

Dubbed ANSI/API RP 100-1 and 100-2, the new standards provide guidance and recommendations for pressure containment and well integrity, as well as environmental safeguards, including groundwater protection, waste management, emissions reduction, site planning, and worker training. The release follows publication of ANSI/API Bulletin 100-3, which outlines community engagement guidelines to assist operators communicate effectively with residents and stakeholders to pursue mutual goals for community growth.

This paper will provide an overview of the developed global standards that emphasize three core principals of integrity, safety and environmental responsibility, and effective communication. Key focus areas of the paper outline how the standards address well integrity and fracture containment, environmental aspects associated with well construction and fracturing operations, and communication guidance for communities and other key stakeholders.
Interaction Between Hydraulic Fracture and a Preexisting Fracture under Triaxial Stress Conditions
Authors: Mighani Saied , Lockner David A. , Kilgore Brian D. , Sheibani Farrokh , Evans Brian
Published: January 2018

Enhanced reservoir connectivity generally requires maximizing the intersection between hydraulic fracture (HF) and preexisting underground natural fractures (NF), while having the hydraulic fracture cross the natural fractures (and not arrest). We have studied the interaction between a hydraulic fracture and a polished saw-cut fault. The experiments include a hydraulic fracture initiating from a pressurized axial borehole (using water) that approaches a dry fault that is inclined at an angle θ with respect to the borehole axis. The experiments are conducted on Poly(methyl) Meta Acrylate (PMMA) and Solnhofen limestone, a finely grained (<5 μm grain), low permeability (<10 nD) carbonate. The confining pressure in all experiments is 5 MPa, while the differential stress (1-80 MPa) and approach angle, θ (30, 45, 60, 90°) are experimental variables. During the hydraulic fracture, acoustic emissions (AE), slip velocity, slip magnitude, stress drop and pore pressure are recorded at a 5 MHz sampling rate. A Doppler laser vibrometer measures piston velocity outside the pressure vessel to infer fault slip duration and a strain gauge adjacent to the saw-cut provides a near-field measure of axial stress.

For PMMA, the coefficient of friction was 0.30 and sliding was unstable (stick-slip). The approaching HF in PMMA created a tensile fracture detected by AE transducers ~100 μs before the significant stick-slip event (45% stress drop and slip velocity of ~60 mm/s) and was arrested by the fault at all fault orientations and differential stresses, even at 90° fault orientation and 80 MPa differential stress. For Solnhofen limestone, we observed stable sliding at a coefficient of friction of 0.12. In contrast to PMMA, the HF in Solnhofen consistently crossed to the other side of the fault. When the HF crossed the fault, it produced a small stress drop (<10%) and slip velocity of only 0.5 mm/s. Theoretical models by Blanton (1986) and Renshaw and Pollard (1995) predict that HF will be arrested for Solnhofen limestone and cross PMMA 90° fault at 80 MPa differential stress. Although the exact cause for the discrepancy between experiments and the theory is not known, one feature present in the experiments but not considered in the models, is the diffusion of fluid driven by the fault slip. Thus, the formation of a "fluid-filled patch" on the fault surface as it is intersected by the HF may substantially impact the crossing/arrest behavior. The approach angle and differential stress also influence the HF initiation azimuth and breakdown pressure. In most cases, the HF initiation azimuth was normal to the fault strike. These observations suggest that the presence of natural fractures could result in rotation of hydraulic fractures to be more normal to their strike and a subsequent change in the downhole pressure recordings. The latter could be used as a diagnostic tool for predicting this interaction.
THE BUZZ AESTHETIC AND MANDE MUSIC: ACOUSTIC MASKS AND THE TECHNOLOGY OF ENCHANTMENT
Authors: Driver Merlyn
Published: January 2018

This article concerns the widespread preference for â€˜buzzyâ€™ timbres in African traditional musics; and, in particular, the ways in which this preference has been borne out in the Mande region of west Africa. The two main types of buzzing mechanisms in Mande music are metal buzzing rattles, which are attached to the neck or bridge of various string instruments, and mirlitons (vibrating membranes), which are placed over small holes on the resonating gourds of wooden xylophones. Over the last seventy to eighty years, an older and rougher â€˜buzz aestheticâ€™ within Mande music has become increasingly endangered, with buzzing largely disappearing from instruments such as the kora and the ngoni in favour of a â€˜cleanerâ€™, more â€˜Westernâ€™ aesthetic. Considered in a wider cultural context, I discuss the possible origins of the Mande buzz aesthetic and attempt to explore how the incorporation of buzzing sounds within Mande music might be connected to forms of â€˜esotericâ€™, â€˜supernaturalâ€™ and spiritual power.