Shale Play Research Articles

Development of shale reservoirs: Knowledge gained from developments in North America

The international daily increase in energy demands requires exploration of new and unconventional energy resources. Unconventional oil and gas have received special attention in recent years as an important source of fossil fuel. This is true especially in North America; United States and Canada, and in other regions in the world including the Middle East.The technological advancements have made the production from unconventional resources possible and more economical. The learning curve and a substantial experience are being developed in North America, where most of the shale developments took place. This paper presents an effort to summarize the current experience on shales of North America from different aspects: rock mechanics, rock/fluids interaction, gas flow mechanisms through shale rocks, proppant embedment and water recovery after shale fracturing.Shale rocks are composed of rock matrix, kerogen, and natural fractures. The mineralogy of shale rocks changes from one field to another. This change in mineralogy will impact the mechanical properties of the shale reservoirs. For example, Haynesville shale becomes more ductile with the increase in its clay content. Similar trends were seen for Lower Bakken shale, while other shale reservoirs, like Eagle Ford, Barnett and Middle Bakken contain more quartz and calcite, which make the rocks harder and easier to fracture. The rock mechanical properties of shale rocks can change as a direct result of the exposure of these clay-sensitive rocks to fracturing fluids. This has been confirmed in literature where Middle Bakken shale lost 52% of its Young's modulus after exposure to slickwater at 300 °F for 48 h.Porosity in unconventional reservoirs can be found in both organic and inorganic parts of the rock. The porosity of the organic matter, and hence the amount of gas stored in kerogen, cannot be neglected and should be considered in the calculation of the gas originally in place. Porosity in organic matter depends on several parameters; among the most important ones is the maturity of the shale itself. Flow of gas in shale rocks is governed mainly by the non-Darcy effects. In addition, gas can be stored and produced from different sources including natural fractures, organic matter and inorganic matrix. Porosity and permeability in organic matter cannot be neglected and it is very important when it comes to storage and flow in shale reservoirs.As a direct result of using different fluid systems in hydraulic fracturing of shale reservoir, an impact on the rock mechanical properties of the rocks were noticed and recorded. This impact can be significant based on several parameters like the temperature, time to exposure and the mineralogy of the shale rock itself. The rock properties can change in a way the rock becomes more ductile and that can increase the proppant embedment in the rock and the overall fracture conductivity to decrease.Among the different fracturing fluid systems used in the field, the use of slickwater in hydraulic fracturing represents a major challenge as a huge volume of water is used in such treatment. In Marcellus shale formation, hydraulic fracturing of one well may require an average volume of 3–8 million gallons of water. Recycling of produced water has been attempted in North America in Marcellus shale play, where re-use of the flowback water resulted in 25% reduction in the fresh water volumes and it reduced the cost of disposing produced water by 45%–55%. A comprehensive understanding and analysis on unconventional reservoirs is required for the Middle Eastern reservoirs. The paper presents a summary of all of these findings from North America.

Concomitant degradation of complex organics and metals recovery from fracking wastewater: Roles of nano zerovalent iron initiated oxidation and adsorption

This work examines the characteristics of fracking wastewater from an emerging shale play in Central China, and the catalytic activity of nano-sized zerovalent iron (n-ZVI) particles to degrade major organic components of fracking wastewater (FW), and to simultaneously recover/remove metals and potential toxic elements. Addition of optimized concentration of n-ZVI (2g/L) to the raw FW led to COD reductions of 30% at pH 4, and 54% at pH 3 (with addition of H2O2) respectively within 120min reaction time. Activity of n-ZVI catalyst on degradation kinetics of total petroleum hydrocarbon (TPH) was over 6 times faster in acidic condition (Krc=0.0029min−1), than at natural pH of the raw FW (Krc=0.00046min−1). Meanwhile, oxidant-assisted degradation of the FW TPH reached higher degradation amounts (C/C0=0.191) at half the time required for treatment without oxidant addition (C/C0=0.218), and thus, implies a reduce treatment cost at shorter reaction time. Moreover, n-ZVI initiated oxidation led to rapid degradation of the FW polyethylene glycols (93.7% PEGs removal), as verified by liquid chromatography/tandem triple quadrupole mass spectrometry (LC–MS/MS), and possible degradation pathway of PEGs by n-ZVI was deduced. Similarly, n-ZVI recover metals and remove potential halocarbon-forming elements like chlorine as confirmed by X-ray fluorescence (XRF) analysis. Furthermore, the n-ZVI catalyst essentially increased biodegradability index of the FW at lower pH, and in the presence of oxidants. Therefore, pre-treatment of FW with n-ZVI represents a potential and cost-effective treatment option for the reuse of fracking wastewaters.

Elemental geochemistry of lower Silurian Longmaxi shale in southeast Sichuan Basin, South China: Constraints for Paleoenvironment

A significant proportion of shale gas resources occurs in Lower Silurian Longmaxi Formation in southeast Sichuan Basin, South China, where commercial gas production has been achieved at Fuling Shale Gas Field. This study area is located adjacent to Fuling Jiaoshiba shale play. Elemental geochemistry regarding paleoenvironment aspects of lower Silurian Longmaxi shale gas is poorly understood. However, the samples in this study are representative, revealing the complete elemental geochemical characteristics of Longmaxi Shale. This research has analysed trace and rare earth elements of lower Silurian Longmaxi Shale and investigated the depositional environment, provenance, and tectonic settings when this type of shale formed. Sedimentary structures include horizontal lamination, massive lamination, and deformation structures that are well developed in black shale and grey silty shale of lower Silurian Longmaxi Formation. Gamma ray, total organic carbon, and pyrite contents are relatively higher in the lower part of the shale. The enrichment of sulfophile heavy metal elements (Cu, Zn, Pb, Mo, Ni) indicates that a reducing environment is common during the deposition of Longmaxi Formation. The concentration of rare earth elements is generally constant with relatively high concentration of light rare earth elements, stable concentration of heavy rare earth elements, and negative Eu anomalies. The sediments of Longmaxi Formation are derived primarily from the sedimentary rocks and granites in continental crust. The combination of trace and rare earth elements indicates that the tectonic settings of the provenance are continental island arc and active continental margin.

Geologic Carbon Storage for Shale Gas Recovery

We consider the feasibility of a novel Carbon Capture, Utilization and Storage (CCUS) concept that consists in producing oil and gas from hydrocarbon-rich shales overlying deep saline aquifers that are candidates for CO2 storage. Such geological overlapping between candidate aquifers for CO2 storage and shale plays exists in several sedimentary basins across the continental US. Since CO2 reaches the storage formation at a lower temperature than the in-situ temperature, a thermal stress reduction occurs, which may lead to hydraulic fracturing of the caprock overlying the aquifer. In this work, we use a thermo-hydro-mechanical approach for modelling a caprock-aquifer-baserock system. We show that hydraulic fracturing conditions are induced within the aquifer by thermal stress reduction caused by cooling and that hydraulic fractures eventually propagate into the lower portion of the shale play. Nonetheless, fracture height of penetration in the caprock is considerably short after 10 years of injection, so the overall caprock sealing capacity is maintained. To maximize the benefit of the proposed CCUS method, CO2 injection should be maintained as long as possible to promote the penetration depth of cooling-induced hydraulic fractures into organic-rich shales. Though drilling a horizontal well in the lower portion of the shale to produce hydrocarbons from the induced hydraulic fractures may not be technically feasible, hydrocarbons can still be produced through the injection well. The production of hydrocarbons at the end of the CO2 storage project will partly compensate the costs of CCS operations.

Characterization of the chemicals used in hydraulic fracturing fluids for wells located in the Marcellus Shale Play

Hydraulic fracturing, coupled with the advances in horizontal drilling, has been used for recovering oil and natural gas from shale formations and has aided in increasing the production of these energy resources. The large volumes of hydraulic fracturing fluids used in this technology contain chemical additives, which may be toxic organics or produce toxic degradation byproducts. This paper investigated the chemicals introduced into the hydraulic fracturing fluids for completed wells located in Pennsylvania and West Virginia from data provided by the well operators. The results showed a total of 5071 wells, with average water volumes of 5,383,743 ± 2,789,077 gal (mean ± standard deviation). A total of 517 chemicals was introduced into the formulated hydraulic fracturing fluids. Of the 517 chemicals listed by the operators, 96 were inorganic compounds, 358 chemicals were organic species, and the remaining 63 cannot be identified. Many toxic organics were used in the hydraulic fracturing fluids. Some of them are carcinogenic, including formaldehyde, naphthalene, and acrylamide. The degradation of alkylphenol ethoxylates would produce more toxic, persistent, and estrogenic intermediates. Acrylamide monomer as a primary degradation intermediate of polyacrylamides is carcinogenic. Most of the chemicals appearing in the hydraulic fracturing fluids can be removed when adopting the appropriate treatments.

The Great Divide: Public Perceptions of Shale Gas Extraction and Hydraulic Fracturing in Pennsylvania and New York

This study compares public perceptions of shale gas extraction and hydraulic fracturing in two of the most populous states with significant shale gas reserves but with vastly different approaches to developing this resource. Drawing on data from a comparative survey administered to two statewide samples in Pennsylvania (n = 411) and New York (n = 404), the study examines the correlates of support for hydraulic fracturing, as well as general levels of public awareness, and perceptions of effects of hydraulic fracturing within the Marcellus shale play. Though the level of awareness of the fracking issue among residents of Pennsylvania and New York is found to be similarly high, levels of support for fracking differ, mirroring distinctive policy approaches found in these neighboring states. The correlates of support for fracking include being Republican, having a conservative ideology, and being male. The study also finds that residents of New York are more aware of fracking policy and debate in Pennsylvania than vice versa, with many New York residents perceiving negative effects on their home state as a result of fracking in neighboring Pennsylvania. This asymmetric level of awareness and concern raises new questions on the role of cross-­border perceptions in shaping opinion toward hydraulic fracturing in adjacent states.

A New Method to Estimate Total Organic Carbon (TOC) Content, an Example from Goldwyer Shale Formation, the Canning Basin

Background:There is an increasing interest in the Goldwyer Formation of the Canning Basin as a potentially prospective shale play. This Ordovician shaly formation is one of the most prominent source rocks in the Canning Basin. One key property to evaluate the prospectivity of any shale oil or gas is its total organic carbon (TOC) richness.Objectives:This study investigates different TOC estimation techniques and validates the reliability of each, aiming to provide a best estimating approach for local and global applications.Method:The limited well distribution in the large area of the Canning Basin makes a basin-wide study not warranted at this stage. A focused look into the Barbwire Terrace was carried out instead. General TOC estimation methods, such as Schmoker and ∆logR were employed for TOC calculation. TOC relationships of single and multivariate regressions were also derived from wireline data and TOC rock sample measurements.Results:Both Schmoker and ∆logR methods tend to overestimate TOC when compared to the available Rock-Eval pyrolysis TOC measurements. The regression approach have shown to provide the best TOC estiamtes for wells in the Barbwire Terrace, where the best multiple regression approach for the terrace and global application was found to be the one derived from gamma-ray (GR), bulk density (RHOB), and sonic log transit time (DT).Conclusion:The generalized nature of the Schmoker method, as it provides a global relationship between density and TOC is probably the main reason why this approach does not provide a good fit in the case of the Goldwyer Formation. Furthermore, the uncertainty associated with the ∆logR method factors, such as the level of maturity (LOM), and resistivity and sonic baselines greatly influence the TOC estimation in this method, and hence, sometimes do not merit a reliable TOC estimation. The multiple regression approach have shown to be most accurate once lithology and compaction information (GR, RHOB, and DT) were incorporated in the regression process. TOC was reliably estimated for wells inside and outside the Barbwire Terrace, and also for wells of a global lacustrine shale. Such derivation have provided a more accurate technical assessment of the shale play and its prospectivity as a potential unconventional hydrocarbon resource.

Visionary planning and the Eagle Ford Shale Play: a cross-case study of rural school superintendents as sense-makers

The decision-making processes used by superintendents in times of economic crises are well documented. Little is known about how they respond/plan in times of economic gains. The purpose of this study is to explore how superintendents respond and plan for the future amidst the changes brought about by oil and gas development of the Eagle Ford Shale (EFS) in South Central Texas. Two research questions guided this qualitative study: in what ways are rural school district superintendents sensemakers and how do they respond to the presence of the EFS Play? Three superintendent’s narratives were represented against a backdrop of structural functionalism and a model of sensemaking. Sensemaking is how the superintendents in our study explained what is going on within their school districts. Despite increased reserves and affluence two issues took precedence: school facilities/physical plants deterioration and declining academic achievement. Each superintendent leveraged the situation as a process to maximise economic benefits to school improvement. The EFS play was viewed as a strategic opportunity to pass/administer school bond elections; to a lesser degree academic improvement. Implications: Rapidly changing economics requires new and increased knowledge of superintendents. Balanced sensemaking will help superintendents with visions of sustained development and improved opportunities.

Using PCA and PLS on publicly available data to predict the extractability of hydrocarbons from shales

Prediction of hydrocarbon extraction from shale requires specialized knowledge of shale play characteristics and analysis to assess effective, economical, and sustainable implementation of oil and natural gas production. In this work, we present a statistical approach that can be used as a preliminary investigation into the hydrocarbon resource potential of a shale play based on limited data. Statistical algorithms for Principal Component Analysis (PCA) and Partial Least Squares Regression (PLS) were used to determine if depositional environments and lithographic boundary characteristics of different plays allowed prediction of specific production parameters. This project characterizes Eagle Ford and Utica formations—two high-producing shale plays in the United States—and Banff/Exshaw and Colorado formations—two recently assessed shale plays in Alberta, Canada. Partial Least Squares Regression models were unable to model gas production parameters from predictor variables, highlighting the complexity of gas formations and the need for data on microscale petrophysical characteristics. In contrast, oil production parameters were better predicted, because bulk variables such as mineral composition appeared to correlate with oil location in mineral interfaces. As expected, a PLS model's predictive capabilities increased with specificity of data sets to particular regions of a shale play. This study indicates how PCA and PLS modeling could assist stakeholders to make preliminary decisions regarding hydrocarbon extraction, especially when limited to publicly available petrophysical data.

Re-appraisal of the Bakken Shale play: Accounting for historic and future oil prices and applying fiscal rates of North Dakota, Montana and Saskatchewan

The ascent of the Bakken shale play as a major U.S. oil producer became threatened by the 2014–2016 oil price fall. This benchmark study assesses and compares the economic performance of typical Bakken wells across three different fiscal regimes: North Dakota (ND) and Montana (MT) in the U.S., and the Canadian province of Saskatchewan (SK). Decline curve analysis and discounted cash flow analysis are applied to evaluate and re-appraise both the productivity and economic performance (internal rate of return, IRR) of typical Bakken wells in each region. For wells of similar estimated ultimate recovery (EUR), the fiscal regime of Montana (IRR 27%) is slightly more advantageous than North Dakota's (IRR 24%). If wells can be identified in SK akin to ND's reference well of 555 Mbbls EUR, the Canadian province provides the most attractive after tax return (180%). However, type curves for Bakken wells in SK and MT analyzed in our study typically have EURs at only 14% and 37% of the ND reference well (EUR∼555 Mbbls) and IRRs adjusted for EUR in MT and SK are negative in both regions at the historic reference price of $80/bbl. A sensitivity analysis using oil prices ranging between $20–100/bbl accounts for any of the price levels seen in the 2014–2016 price fall, and can be projected forward. The evaluation of single well economics and sensitivity to oil price changes and drilling and completion cost is subsequently expanded with a representative firm approach considering certain asset development options with multiple wells in each of the three Bakken jurisdictions (ND, MT, SK).

Attitudes Toward “Fracking”: Perceived and Actual Geographic Proximity

AbstractPrior surveys have sought to gauge American public opinion toward shale gas development. Research on environmental hazards has produced conflicting findings related to the role of proximity in predicting attitudes. This study analyzes how perceived and actual proximity to active shale gas development in Pennsylvania, Ohio, and Texas predicts individual preferences for moratoria. We implement a conditionally parametric probit, which accounts for geographic variation in coefficient values. Our results suggest that attitudes toward the potential benefits and risks associated with shale gas development play a larger and more consistent role in predicting preference for moratoria than proximity or other sociodemographic factors. Our methodology allows for inferences related to the extent of geographic variation in coefficient values. Our results indicate that the role of proximity in predicting preference for moratoria differs based on whether a respondent resides in an urban or rural area or within a shale play.

An improved model for estimating the TOC in shale formations

Determination of the total organic carbon (TOC) from well logs is an important step in formation evaluation of shale reservoirs. The ΔlogR model is one of the most commonly used methods in determining the TOC of the source rocks. Wang et al. (2016) made three revisions on ΔlogR model to enhance the prediction accuracy, one of which is to use a changeable slope of log10Rt versus porosity logs to replace a fixed value. Based on the original ΔlogR model and Wang's revision, we propose an improved model for a better TOC estimation in this paper. Specifically, the approximate linear baseline is replaced by a theoretical one. Under this condition, both the slope and resistivity and porosity log values of the baselined rocks vary from depth to depth. The determination of theoretical baseline is presented, and the varied baseline log values are obtained by a simple mathematical technique. In addition to the shale play of Western Canada Sedimentary Basin, two study areas of Sichuan Basin and Ordos Basin in China, were used to assess the applications of the proposed model and its improvement over the original model. The analysis and discussions presented in this paper indicate that the improved model offers more reliable results in shale plays with large lithological variations. Also, the TOC content of the three study areas was estimated using the proposed model. The results showed that the TOC values estimated from well logs and core analysis are in good agreement.

Controls on Methane Occurrences in Aquifers Overlying the Eagle Ford Shale Play, South Texas.

Assessing natural vs. anthropogenic sources of methane in drinking water aquifers is a critical issue in areas of shale oil and gas production. The objective of this study was to determine controls on methane occurrences in aquifers in the Eagle Ford Shale play footprint. A total of 110 water wells were tested for dissolved light alkanes, isotopes of methane, and major ions, mostly in the eastern section of the play. Multiple aquifers were sampled with approximately 47 samples from the Carrizo-Wilcox Aquifer (250-1200 m depth range) and Queen City-Sparta Aquifer (150-900 m depth range) and 63 samples from other shallow aquifers but mostly from the Catahoula Formation (depth <150 m). Besides three shallow wells with unambiguously microbial methane, only deeper wells show significant dissolved methane (22 samples >1 mg/L, 10 samples >10 mg/L). No dissolved methane samples exhibit thermogenic characteristics that would link them unequivocally to oil and gas sourced from the Eagle Ford Shale. In particular, the well water samples contain very little or no ethane and propane (C1/C2+C3 molar ratio >453), unlike what would be expected in an oil province, but they also display relatively heavier δ13 Cmethane (>-55‰) and δDmethane (>-180‰). Samples from the deeper Carrizo and Queen City aquifers are consistent with microbial methane sourced from syndepositional organic matter mixed with thermogenic methane input, most likely originating from deeper oil reservoirs and migrating through fault zones. Active oxidation of methane pushes δ13 Cmethane and δDmethane toward heavier values, whereas the thermogenic gas component is enriched with methane owing to a long migration path resulting in a higher C1/C2+C3 ratio than in the local reservoirs.

Fracture Modeling Using a Constructed Discrete Fracture Network From Seismic Data

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 179130, “Calibrated Complex Fracture Modeling Using a Constructed Discrete Fracture Network From Seismic Data in the Avalon Shale, New Mexico,” by Foluke Ajisafe, Manoj Thachaparambil, Donald Lee, Ben Flack, Kim Hemsley, Efe Ejofodomi, and Christopher Taylor, Schlumberger, prepared for the 2016 SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, USA, 9–11 February. The paper has not been peer reviewed. The objective of this study is to validate the concept of using a seismically derived discrete fracture network (DFN) calibrated with borehole measurements, for complex-hydraulic-fracture modeling. This study was applied successfully on a two-well horizontal pad in the Avalon Shale located in the Delaware Basin, New Mexico. The work flow presented in this paper shows the successful application of seismic data in creating DFNs required to model hydraulic fractures in unconventional reservoirs. Introduction In the past, hydraulic-fracture modeling was limited to planar models for conventional reservoirs, with the absence of natural fractures. In unconventional reservoirs, planar models are highly limited in properly simulating complex fracture geometries. In recent years, a state-of-the-art complex- fracture-network model, also known as an unconventional fracture model (UFM), was developed. The model simulates the fracture propagation, rock deformation, and fluid flow in the complex fracture network created during a treatment. A key difference between the UFM and the conventional planar-fracture model is the ability to simulate the interaction of hydraulic fractures with pre-existing natural fractures. In shale plays, conventional DFN models are built out of 1D fracture-dip interpretation from a borehole-image log or from core in the same or a nearby well. However, because the hydraulic fractures created during a stimulation treatment usually extend hundreds of feet away from the wellbore, it is important to characterize and understand the natural fractures away from the wellbore. Therefore, a more-accurate DFN model than the simple conventional model is crucial in unconventional plays for optimizing well spacing and stimulation design to ultimately achieve maximum effective drainage while maximizing returns. In this study, the authors use an established work flow for extracting seismic-scale fracture networks and extending their population properties to model corresponding subseismic fractures that are critical to understanding and calibrating complex-hydraulic-fracture geometry created during stimulation. Geology The Avalon unconventional shale play consists of siltstone, limestone, clay, chert, and organics. It can be subdivided into three zones: upper, middle, and lower. In the past, the Avalon shale has been exploited by vertical drilling, but recently, horizontal drilling has been the trend to fully exploit this unconventional play.

Hydraulic Fracturing Conference Offers New Insights

Conference review The SPE Hydraulic Fracturing Technology Conference and Exhibition took place 24–26 January in The Woodlands, Texas. The event included more than 50 technical paper presentations, as well as 90 exhibitors, discussing and showcasing new hydraulic fracturing technologies, various applications, and learnings from fracture-stimulated wells. Below are some of the highlights from the conference. Initial Impressions of Wells May Be Misleading Stephen Rassenfoss, JPT Emerging Technology Senior Editor The mostly widely reported production data proved to be a bad indicator of future output. A study presented at the conference considered whether the widely reported 30-day production total is a good way to evaluate a well compared with less frequently offered longer-term numbers. “Production at 30 days tends to be an unreliable estimate,” said Edward Ifejika, a field operations engineer for Total who did the research while he was a student at Texas A&amp;M University (SPE 184817). The number after 90 days offers a much better estimate of future gas production and the improvement from there is limited. Getting a Better Look at Propped Fractures Stephen Rassenfoss, JPT Emerging Technology Senior Editor Carbo Ceramics is getting a clearer look at where the proppant goes. The ceramic proppant maker showed much-improved images at this year’s conference (SPE 184880) compared with the ones shown last year, as well as a new set of images showing three stages of a Marcellus gas well. The presentation at the start of the conference’s technical sessions drew a large crowd. The method discussed uses metallically coated ceramic proppant that is activated by an electric current run through the reservoir. The new method promises a deep look that is not available using alternatives such as radioactive markers, which are visible only within a couple feet of the wellbore. Think-Tank Founder Touts Benefits of Fossil Fuels Trent Jacobs, JPT Digital Editor Higher life expectancy, plentiful food, and soaring gross domestic product are among the benefits that much of the world’s population has enjoyed since widespread use of fossil fuels began more than a century ago. They are also the central pillars to Alex Epstein’s the-sis of why fossil fuel production, and the engineering involved, equates to a moral obligation. Epstein, founder of the for-profit think tank Center for Industrial Progress and author of The Moral Case for Fossil Fuels, was the featured speaker of this year’s conference. Addressing several hundred industry professionals, Epstein used the rise of the North American shale sector to highlight how, despite making possible the many advantages of living in the modern age, the wider oil and gas industry is losing the public relations battle. Institute Seeks To Boost Knowledge in Permian Basin Trent Jacobs, JPT Digital Editor For all of the upstream activity going on in the Permian Basin of Texas, it can be difficult to assess which horizontal well strategies are working best and why. The primary reason is operators in Texas are not required to share as much detailed drilling and completion information as they are in other major oil-producing states such as North Dakota, home to one of the shale sector’s most revered public databases. But with the recent formation of the Texas Oil and Gas Institute (TOGI), it is expected that the Permian will soon become a much more well understood shale play. TOGI was established in 2015 by the regents of the University of Texas (UT) system, which manages oil and gas mineral rights across 2 million acres of land in west Texas. Saudis Find Proppant Source in Their Own Back Yards Stephen Rassenfoss, JPT Emerging Technology Senior Editor When hydraulic fracturing arrived in Saudi Arabia, there was something lacking. While the reserves of tight gas are bountiful and sand covers the desert, Saudi Aramco has had to import ceramic proppant to hold open the fractures created. Sand dunes in its deserts provide a seemingly endless supply of sand, but when the national oil company studied those grains of sand, it found that they were “nice and round but not very strong,” said Kirk Bartko, a senior petroleum engineering consultant for Saudi Aramco, during a presentation at the conference (SPE 184823). It was a second-grade proppant, which was not quite up to the demand of wells typically 10,000 ft deep where proppant faces closure pressures of about 11,000 psi. The likely result would be sand grains crushed into fine particles likely to block the flow of gas.

Methane Occurrences in Aquifers Overlying the Barnett Shale Play with a Focus on Parker County, Texas.

Clusters of elevated methane concentrations in aquifers overlying the Barnett Shale play have been the focus of recent national attention as they relate to impacts of hydraulic fracturing. The objective of this study was to assess the spatial extent of high dissolved methane previously observed on the western edge of the play (Parker County) and to evaluate its most likely source. A total of 509 well water samples from 12 counties (14,500 km2 ) were analyzed for methane, major ions, and carbon isotopes. Most samples were collected from the regional Trinity Aquifer and show only low levels of dissolved methane (85% of 457 unique locations <0.1 mg/L). Methane, when present is primarily thermogenic (δ13 C 10th and 90th percentiles of -57.54 and -39.00‰ and C1/C2+C3 ratio 10th, 50th, and 90th percentiles of 5, 15, and 42). High methane concentrations (>20 mg/L) are limited to a few spatial clusters. The Parker County cluster area includes historical vertical oil and gas wells producing from relatively shallow formations and recent horizontal wells producing from the Barnett Shale (depth of ∼1500 m). Lack of correlation with distance to Barnett Shale horizontal wells, with distance to conventional wells, and with well density suggests a natural origin of the dissolved methane. Known commercial very shallow gas accumulations (<200 m in places) and historical instances of water wells reaching gas pockets point to the underlying Strawn Group of Paleozoic age as the main natural source of the dissolved gas.

Ono–Kondo Model for Supercritical Shale Gas Storage: A Case Study of Silurian Longmaxi Shale in Southeast Chongqing, China

Shale gas storage is a dominant factor to economically evaluate the shale play. A series of Lower Silurian Longmaxi marine shale samples in southeast Chongqing, China, were collected to investigate the reservoir characteristics, and a suit of methane adsorption isotherms were fitted using a supercritical Ono–Kondo model to better understand the adsorption capacity of Longmaxi shale. The saturated adsorption of a monolayer presents a greatly positive relationship with the total organic carbon (TOC) content. A negative relationship with clay was observed due to the predominant influence of organic matter on the methane adsorption. Methane adsorption also increases with increasing pressure and decreases with increasing temperature. On the basis of the relationships, one new estimation algorithm related to TOC content, pressure, and temperature was established to calculate the methane adsorption capacity on the basis of the Ono–Kondo model. Furthermore, with higher TOC content, the adsorption capacity of shal...

Game theory approach to optimal design of shale gas supply chains with consideration of economics and life cycle greenhouse gas emissions

This article addresses the optimal design of a non‐cooperative shale gas supply chain based on a game theory approach. Instead of assuming a single stakeholder as in centralized models, we consider different stakeholders, including the upstream shale gas producer and the midstream shale gas processor. Following the Stackelberg game, the shale gas producer is identified as the leader, whose objectives include maximizing its net present value (NPV) and minimizing the life cycle greenhouse gas (GHG) emissions. The shale gas processor is identified as the follower that takes actions after the leader to maximize its own NPV. The resulting problem is a multiobjective mixed‐integer bilevel linear programming problem, which cannot be solved directly using any off‐the‐shelf optimization solvers. Therefore, an efficient projection‐based reformulation and decomposition algorithm is further presented. Based on a case study of the Marcellus shale play, the non‐cooperative model not only captures the interactions between stakeholders but also provides more realistic solutions. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2671–2693, 2017

The Performance improvements of a New Drilling Agitator Devicein Jiaoshiba Shale Gas well

In order to solve the backing pressure and high friction, a newdrilling agitator device was used in directional and horizontal drilling in Jiaoshiba area of Fuling, Chongqing, China.Due to Jiaoshiba region geological situations are complex, backing pressure and Stick-Slip are always existing in directional drilling, this source of additional torque and drag will lead to low ROP(rates of penetration), poor tool face control, short runs, severe drill string and bit wear, in directional and horizontal applications, this high friction could also lead to high well tortuosity, which will limit the amount of step out and can even impair productivity. The implementation of a unique tool, referred to as a Drilling Agitator Tool (DAT), has demonstrated clear improvement in drilling performance by reducing stick slip and torque at the drill string in Jiaoshiba area. This has enabled reduction in drag and thus improved weight transfer to the bit when drilling through highly interbedded formations, directional applications or long horizontal sections. It has also shown greater accuracy in maintaining tool face control once the static friction was minimized.This paper illustrates case studies from the Jiaoshiba Shale Plays, where the DAT has proven to help reduce torque and Stick-Slip when run on rotary in vertical applications, as well as Motor assemblies through directional and horizontal sections. These improvements in drilling performance have resulted in longer runs and faster ROP compared to offset wells, thus reducing the number of bits and improving the economics in drilling Jiaoshiba shale plays. Selecting high-efficiency PDC bit and screw together with DAT in Jiaoshiba shale gas well can accomplish “one single bit run”.

Regulated Gaseous Emissions from In-use High Horsepower Drilling and Hydraulic Fracturing Engines

Unconventional well development is an energy intensive process, which relies heavily on diesel fuel to power high-horsepower engines. To reduce emissions and fuel costs, and increase natural gas utilization, industry has employed a limited number of dual fuel compression-ignited and dedicated natural gas spark-ignited engines. However, little in-use data are available for conventional engines or these new technologies. We measured regulated gaseous emissions from engines servicing the unconventional natural gas well development industry to understand better their in-use characteristics such that insight into real world emissions factors could be developed for use by researchers, regulators, or industry. Data collection efforts were limited by low utilization of these new technologies, therefore these data may not be representative of the current distribution of engines either nationally or by shale play. Emissions and fuel consumption were collected from two drilling engines operating as Tier 2 diesel only and dual fuel, two drilling engines that were dedicated natural gas, and two hydraulic fracturing engines operated as diesel only and dual fuel. Emissions for diesel only operation were below Tier 2 certification standards for carbon monoxide and non-methane hydrocarbon plus oxides of nitrogen. Dual fuel engines require use of oxidation catalysts to reduce carbon monoxide and non-methane hydrocarbon emissions resulting from this mode of combustion. For dual fuel engines with diesel oxidation catalysts, carbon monoxide emissions were reduced below Tier 2 diesel only standards by an order of magnitude. Dual fuel operation showed varied effects on non-methane hydrocarbon plus oxides of nitrogen emissions depending on configuration. These variations were mainly driven by some technologies increasing or decreasing oxides of nitrogen emissions. One dual fuel drilling engine failed to meet Tier 2 standards, as it did not include a diesel oxidation catalyst. Of the two dedicated natural engines tested, one had a failed catalyst and did not meet off-road standards for spark-ignited engines; however, emissions from the engine with the properly functioning catalyst were well below standards. Dedicated natural gas engines also demonstrated potential to meet Tier 2 carbon monoxide regulations while producing significantly lower oxides of nitrogen emissions than diesel only or dual fuel engines.