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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "H: Geo-Energy".

Deadline for manuscript submissions: closed (31 October 2019) | Viewed by 39704

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Special Issue Editors

Dr. José A. Torres

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Guest Editor

Computational Hydrocarbon Laboratory for Optimized Energy Efficiency, University of Pau and Pays de l’Adour, 64012 Pau, France
Interests: reservoir engineering; reservoir simulation; enhanced oil recovery; unconventional reservoirs; data analysis; machine learning; advanced reservoir monitoring systems
Special Issues, Collections and Topics in MDPI journals

Dr. Hector Klie

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Guest Editor

1. CEO at DeepCast.ai, 800 Town & Country Blvd, STE # 300, Houston, TX 77024, USA
2. Adjunct Professor at the Department of Computational & Applied Mathematics, Rice University, Houston, TX 77005, USA
Interests: data science; artificial intelligence; computational science; reservoir simulation; high performance algorithms; optimization; uncertainty quantification

Special Issue Information

Dear Colleagues,

We are pleased to invite you to submit papers to the journal Energies for a Special Issue that will be entirely devoted to “Shale Oil and Shale Gas Resources”. The Special Issue will expand on essential technical challenges for improving the understanding and management of these unconventional reservoirs. This Special Issue will serve as an excellent channel for sharing information and lessons learned, collected from different plays.

The relatively short production span observed in unconventional reservoirs demands novel solutions for optimizing drilling, completion, and improved recovery efficiencies. On the other hand, the consolidation and analysis of multiple sources of data are becoming key enablers for the discovery of strong production drivers and building predictive models for complex rock–fluid interactions on fractured media. This issue will seek to ignite contrasting perspectives towards optimal shale play management.

Potential topics of interest include, but are not limited to:

Advances in shale reservoir characterization techniques and workflows;
Analysis of physical-chemical interactions of shale rocks with drilling, injected, or in-situ fluids;
Novel technologies to address the complex challenges in the modeling and simulation of hydrocarbon production from shale formations;
Geomechanical aspects and impacts on shale reservoirs;
Novel methods for enhanced hydrocarbon recovery in shale reservoirs;
Machine learning and data science applications for unlocking new insights in shale resources exploitation.

Dr. José A. Torres
Dr. Hector Klie
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

unconventional resources
shale gas
shale oil
shale plays
fractured media
hydraulic fracturing
completions
coupled flow and geomechanics
machine learning
data-driven models

Published Papers (11 papers)

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Research

20 pages, 7832 KiB

Open AccessArticle

Impact of Shale Anisotropy on Seismic Wavefield

by Han Li, Xiwu Liu, Xu Chang, Ruyue Wu and Jiong Liu

Energies 2019, 12(23), 4412; https://0-doi-org.brum.beds.ac.uk/10.3390/en12234412 - 20 Nov 2019

Cited by 7 | Viewed by 2839

Abstract

During unconventional resources exploration, ignoring shale anisotropy may lead to wrong seismic interpretations, thus affecting the accuracy and credibility of sweet spots prediction and reservoir characterization. In order to investigate the impact of shale anisotropy on the seismic wavefield, we propose a quantitative evaluation method by calculating the waveforms’ amplitude and phase deviations. Based on the 3D elastic wave equation and the staggered-grid finite-difference method, the forward modeling theory with the consideration of shale anisotropy is established. Then, we use the envelope misfit (EM) and phase misfit (PM) parameters to illustrate the differences in waveforms’ amplitude and phase morphology, which are caused by anisotropy. Lastly, by comparing the waveforms of the models with/without anisotropy and calculating their EM and PM values, a practical and quantitative evaluation method is constructed. We used synthetic models of different complexity and oilfield models to validate the proposed method. Through the research, we also gained some new insights about the anisotropy’s effects. For a certain medium model, the impact of shale anisotropy on seismic wavefield is complicated and needs specific analysis. The proposed method provides a useful and quantitative tool for the evaluation of shale anisotropy’s impact. Full article

(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)

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12 pages, 3432 KiB

Open AccessArticle

Experimental Investigation of the Effects of Drilling Fluid Activity on the Hydration Behavior of Shale Reservoirs in Northwestern Hunan, China

by Han Cao, Zheng Zhang, Ting Bao, Pinghe Sun, Tianyi Wang and Qiang Gao

Energies 2019, 12(16), 3151; https://0-doi-org.brum.beds.ac.uk/10.3390/en12163151 - 16 Aug 2019

Cited by 15 | Viewed by 2779

Abstract

The interaction between drilling fluid and shale has a significant impact on wellbore stability during shale oil and gas drilling operations. This paper investigates the effects of the drilling fluid activity on the surface and osmotic hydration characteristics of shale. Experiments were conducted to measure the influence of drilling fluid activity on surface wettability by monitoring the evolution of fluid-shale contact angles. The relationship between drilling fluid activity and shale swelling ratio was determined to investigate the osmotic hydration behavior. The results indicate that, with increasing drilling fluid activity, the fluid–shale contact angles gradually increase—the higher the activity, the faster the adsorption rate; and the stronger the inhibition ability, the weaker the surface hydration action. The surface adsorption rate of the shale with a KCl drilling fluid was found to be the highest. Regarding the osmotic hydration action on the shale, the negative extreme swelling ratio (b) of the shale was found to be: b_KCl < b_CTAB < b_SDBS. Moreover, based on the relationship between the shale swelling ratio and drilling fluid activity, shale hydration can be divided into complete dehydration, weak dehydration, surface hydration, and osmotic hydration, which contributes to the choice of drilling fluids to improve wellbore stability. Full article

(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)

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16 pages, 7318 KiB

Open AccessArticle

High Throughput Screening and Characterization Methods of Jordanian Oil Shale as a Case Study

by Ziad Abu El-Rub, Joanna Kujawa, Esra’a Albarahmieh, Nafisah Al-Rifai, Fathieh Qaimari and Samer Al-Gharabli

Energies 2019, 12(16), 3148; https://0-doi-org.brum.beds.ac.uk/10.3390/en12163148 - 16 Aug 2019

Cited by 6 | Viewed by 3824

Abstract

Oil shale is an important possible solution to the problem of energy in Jordan. To explore the technical and the economic feasibility of oil shale deposits, numerous samples are analyzed using the standard Fischer Assay (FA) method. However, it would be useful to develop faster, cheaper, and reliable methods for determining the oil content of oil shale. Therefore, the aim of this work was to propose and investigate rapid analytical techniques for the screening of oil shale deposits and to correlate them with the FA method. The Omari deposit located east of Jordan was selected as a case study for analysis using thermogravimetric analysis (TGA) coupled with Fourier-transform infrared (FTIR), differential scanning calorimetry (DSC), elemental analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis. Results obtained from the TGA method were linearly correlated with FA with high regression factor (R² = 0.99); a quadratic correlation (R² = 0.98) was maintained between the FA and the elemental hydrogen mass content, and a quadratic correlation (R² = 0.97) was found between the FA and the aliphatic hydrocarbons (FTIR peak at 2927 cm⁻¹) produced in the pyrolysis zone. Although other techniques were less correlated, further investigation might lead to better results. Subsequently, these correlated techniques can be a practical alternative to the conventional FA method when, in particular, specific correlation is made for each deposit. Full article

(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)

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11 pages, 1505 KiB

Open AccessArticle

Study on the Mechanism of Ionic Stabilizers on Shale Gas Reservoir Mechanics in Northwestern Hunan

by Pinghe Sun, Junyi Zhu, Binkui Zhao, Xinxin Zhang, Han Cao, Mingjin Tian, Meng Han and Weisheng Liu

Energies 2019, 12(12), 2453; https://0-doi-org.brum.beds.ac.uk/10.3390/en12122453 - 25 Jun 2019

Cited by 3 | Viewed by 3295

Abstract

The shale of the lower Cambrian Niutitang formation in northwestern Hunan is an ideal reservoir for shale gas. There is a close connection between borehole stability and drilling fluid in shale gas drilling. Ionic stabilizer is a new type of stratum consolidation agent that inhibits the hydration expansion of clay minerals and improves mechanical strength of the borehole. The traditional idea of pore wall protection is to use drilling fluid additives to prevent shale from interacting with water. However, ionic stabilizer can change the hydrophilic of clay minerals in shale, making the particles become hydrophobic and dense, therefore, the formation stability can be enhanced simultaneously. The material used in this paper is different from the normal ionic stabilizer, some chemical bonds that have been changed in the new material called enhanced normality ionic (ENI) stabilizer. This paper utilized the shale samples those obtained from Niutitang formation to study the connection between ENI and the mechanical properties of shale. Mechanical tests and microscopic pore tests were performed on different samples which were soaked in water and the ENI with different concentrations. It has been found through tests that ENI can inhibit the development of shale pores, and as the concentration increases, the inhibition increases. In addition, as the ENI concentration increases, the uniaxial compressive strength and Young’s modulus of the shale increase, and the ratio of stability coefficients decreases. It can be concluded that the ENI can improve the mechanical strength of carbon shale, and prevent the development of rock damage. Moreover, it can improve the ability of rock to resist damage, and enhance borehole stability initiatively. Full article

(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)

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22 pages, 6286 KiB

Open AccessArticle

Enhanced Tight Oil Recovery by Volume Fracturing in Chang 7 Reservoir: Experimental Study and Field Practice

by Long Yu, Jinjie Wang, Chong Wang and Daixin Chen

Energies 2019, 12(12), 2419; https://0-doi-org.brum.beds.ac.uk/10.3390/en12122419 - 24 Jun 2019

Cited by 13 | Viewed by 3519

Abstract

The Chang 7 reservoir in Changqing oilfield is rich in tight oil. However, due to the low formation permeability, it is very difficult to obtain economical oil production without stimulation treatments. Volume fracturing seems to be a more efficient tight oil recovery enhancement (EOR) method in Chang 7 pilot tests compared with conventional hydraulic fracturing. In this study, Chang 7 tight oil reservoir was first characterized by its geological property, hydrocarbon source rock distribution, and formation physiochemical property. Tight core flooding tests were then conducted to experimentally investigate the EOR ability of the volume fracturing technique. The field-scale practice was also demonstrated and analyzed. The results show that Chang 7 reservoir is favorable for the generation of a large amount of tight oil. Fractures created in tight cores can significantly improve the fluid flow conductivity and enhance the imbibition of displacing water, resulting in a greater tight oil recovery increment. Volume fracturing is an effective way to generate a larger number of fractures. Field application indicates that volume fracturing treatment can form a much greater reservoir stimulation volume. Daily oil production in the volume-fracturing-treated wells can be more than twice as high as that in the conventional-fracturing-treated wells. Full article

(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)

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14 pages, 3696 KiB

Open AccessArticle

A Data-Driven Workflow Approach to Optimization of Fracture Spacing in Multi-Fractured Shale Oil Wells

by Xu Yang and Boyun Guo

Energies 2019, 12(10), 1973; https://0-doi-org.brum.beds.ac.uk/10.3390/en12101973 - 23 May 2019

Viewed by 3364

Abstract

A data-driven workflow approach is presented in this study for optimizing fracture spacing of multifractured horizontal wells (MFHW) in shale oil reservoirs. The workflow employs a simple well productivity model for the initial design of hydraulic fracturing well completions. This provides a transparent approach to the identification of key fracturing parameters affecting well productivity. The workflow uses transient pressure or production data to identify fracture interference. This offers a reliable and cost-effective means for assessment of well production potential in terms of optimization of fracture spacing in the MFHW. Result of a field case study indicated that three wells were drilled in an area with dense natural fractures, and the fracture spacing of MFHW in this area was short enough to effectively drain the stimulated reservoir volume (SRV), while the other three wells were drilled in an area with less natural fractures, and the fracture spacing of MFHW in this area could be shortened to double well productivity. Full article

(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)

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9 pages, 3456 KiB

Open AccessArticle

Dynamic Crack Initiation Toughness of Shale under Impact Loading

by Guoliang Yang, Xuguang Li, Jingjiu Bi and Shuaijie Cheng

Energies 2019, 12(9), 1636; https://0-doi-org.brum.beds.ac.uk/10.3390/en12091636 - 30 Apr 2019

Cited by 4 | Viewed by 2379

Abstract

The impact loading of a notched semi-circular bend (NSCB) specimen of outcrop shale in Changning Sichuan was carried out using a split Hopkinson pressure bar (SHPB) to study the effect of shale bedding on the dynamic crack initiation toughness. Three loading configurations were tested: Crack-divider, Crack-splitter and Crack-arrester loading. Bedding plane has a significant effect on the crack initiation of shale. Under the Crack-divider and Crack-splitter modes, shale had lower dynamic crack initiation toughness. The dynamic crack initiation toughness of the shale was affected by the loading rate for all three loading configurations. The correlation between loading rate and dynamic crack initiation toughness was most significant for the Crack-arrester mode, while the Crack-splitter mode was the weakest. When loading was carried out on Crack-arrester, the bedding plane could change the direction of crack growth. In the Crack-splitter mode, only a small impact energy was needed to achieve effective expansion of a crack. The research results provide a theoretical basis for shale cracking. Full article

(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)

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21 pages, 12781 KiB

Open AccessArticle

Shales Leaching Modelling for Prediction of Flowback Fluid Composition

by Andrzej Rogala, Karolina Kucharska and Jan Hupka

Energies 2019, 12(7), 1404; https://0-doi-org.brum.beds.ac.uk/10.3390/en12071404 - 11 Apr 2019

Cited by 1 | Viewed by 2880

Abstract

The object of the paper is the prediction of flowback fluid composition at a laboratory scale, for which a new approach is described. The authors define leaching as a flowback fluid generation related to the shale processing. In the first step shale rock was characterized using X-ray fluorescence spectroscopy, X-ray diffractometry and laboratory analysis. It was proven that shale rock samples taken from the selected sections of horizontal well are heterogeneous. Therefore, the need to carry a wide range of investigations for highly diversified samples occurred. A series of leaching tests have been conducted. The extracts were analyzed after leaching to determine Total Organic Carbon and selected elements. For the results analysis significant parameters were chosen, and regression equations describing the influence of rocks and fracturing fluid parameters on the flowback fluid composition were proposed. Obtained models are described by high values of determination coefficients with confidence coefficients above 0.99 and a relatively low standard deviation. It was proven that the proposed approach regarding shale leaching can be properly described using shale models at a laboratory scale, however scaling up requires further investigations. Full article

(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)

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15 pages, 8864 KiB

Open AccessArticle

Organic Matter Pore Characterization of the Wufeng-Longmaxi Shales from the Fuling Gas Field, Sichuan Basin: Evidence from Organic Matter Isolation and Low-Pressure CO₂ and N₂ Adsorption

by Zhuo Li, Zhenxue Jiang, Hailong Yu and Zhikai Liang

Energies 2019, 12(7), 1207; https://0-doi-org.brum.beds.ac.uk/10.3390/en12071207 - 28 Mar 2019

Cited by 12 | Viewed by 2472

Abstract

Organic matter (OM) pores are significant for shale gas accumulation and flow mechanisms. The pores of Wufeng-Longmaxi (W-L) shale in the Sichuan Basin, China have been extensively characterized, however, the proportion of OM pores in this shale have not been adequately discussed. In this study, the contribution of OM pores to the total pore volume of W-L shale was quantitatively studied through the analysis of OM isolation, field emission scanning electron microscopy (FE-SEM) and low-pressure CO₂ and N₂ adsorption (LPGA). FE-SEM images showed abundant OM pores, interparticle pores and intraparticle pores with various shapes and widths in the W-L shales. The pore size distribution (PSD) of the isolated OM from five shale samples showed a consistent, unimodal pattern. The pore volume of isolated OM was greater than that of the bulk shale samples, suggesting that OM is more porous than the inorganic compositions in shales. The average contribution of OM to the volumes of micropores, mesopores and macropores was 58.42%, 10.34% and 10.72%, respectively. Therefore, the pore volume of the W-L shale was dominantly related to inorganic minerals. This was probably due to the small weight ratio of OM in the shale samples (1.5 wt%–4.2 wt%). The findings of this study reveal the different effects of OM and minerals on pore development, and provide new insights into the quantitative contribution of OM pores to the total pore volume of the W-L shale. Full article

(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)

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15 pages, 6405 KiB

Open AccessArticle

Investigation of Elastomer Seal Energization: Implications for Conventional and Expandable Hanger Assembly

by Harshkumar Patel and Saeed Salehi

Energies 2019, 12(4), 763; https://0-doi-org.brum.beds.ac.uk/10.3390/en12040763 - 25 Feb 2019

Cited by 14 | Viewed by 5920

Abstract

Elastomer seals are extensively used in various wellhead and casing/liner hanger equipment as barriers for isolating fluids. Seal assemblies have been identified as one of the major cause of well control incidents. Majority of hangers utilize conventional weight- or mechanical-set slip-and-seal assembly. The objective of this paper is to conduct a detailed investigation of seal energization in conventional and relatively newer expandable type hanger seal assembly. To achieve the objective, the finite element modeling approach was employed. Three dimensional computer models consisting of concentric casings and annular elastomer seal element were constructed. Seal energization process was modelled by manipulating boundary conditions. Conventional seal energization was mimicked by applying rigid support at the bottom of elastomer element and compressing it from the top. Expandable hanger type seal energization was modelled by radially displacing the inner pipe to compress annular seal element. Seal quality was evaluated in terms of contact stress values and profile along the seal-pipe interface. Different amounts of seal energization were simulated. Both types of seal energization processes yielded different contact stress profiles. For the same amount of seal volumetric compression, contact stress profiles were compared. In case of conventional seal energization, contact stress profile decreases from the compression side towards support side. The seal in expandable hanger generates contact stress profile that peaks at the center of contact interface and reduces towards the ends. Convectional seal assembly has more moving parts, making it more prone to failure or under-energization. Finite Element Models were validated using analytical equations, and a good match was obtained. The majority of research related to elastomer seal is focused on material properties evaluation. Limited information is available in public domain on functional design and assessment of seal assembly. This paper adds novel information by providing detailed assessment of advantages and limitations of two different seal energization process. This opens doors for further research in functional failure modes in seal assembly. Full article

(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)

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22 pages, 10410 KiB

Open AccessArticle

Mechanisms and Influence of Casing Shear Deformation near the Casing Shoe, Based on MFC Surveys during Multistage Fracturing in Shale Gas Wells in Canada

by Yan Xi, Jun Li, Gonghui Liu, Jianping Li and Jiwei Jiang

Energies 2019, 12(3), 372; https://0-doi-org.brum.beds.ac.uk/10.3390/en12030372 - 24 Jan 2019

Cited by 22 | Viewed by 4830

Abstract

Casing shear deformation has become a serious problem in the development of shale gas fields, which is believed to be related to fault slipping caused by multistage fracturing, and the evaluation of the reduction of a casing’s inner diameter is key. Although many fault slipping models have been published, most of them have not taken the fluid-solid-heat coupling effect into account, and none of the models could be used to calculate the reduction of a casing’s inner diameter. In this paper, a new 3D finite element model was developed to simulate the progress of fault slipping, taking the fluid-solid-heat coupling effect during fracturing into account. For the purpose of increasing calculation accuracy, the elastoplastic constitutive relations of materials were considered, and the solid-shell elements technique was used. The reduction of the casing’s inner diameter along the axis was calculated and the calculation results were compared with the measurement results of multi-finger caliper (MFC) surveys. A sensitivity analysis was conducted, and the influences of slip distance, casing internal pressure, thickness of production and intermediate casing, and the mechanical parameters of cement sheath on the reduction of a casing’s inner diameter in the deformed segment were analyzed. The numerical analysis results showed that decreasing the slip distance, maintaining high pressure, decreasing the Poisson ratio of cement sheath, and increasing casing thickness were beneficial to protect the integrity of the casing. The numerical simulation results were verified by comparison to the shape of MFC measurement results, and had an accuracy up to 90.17%. Results from this study are expected to provide a better understanding of casing shear deformation, and a prediction method of a casing’s inner diameter after fault slipping in multistage fracturing wells. Full article

(This article belongs to the Special Issue Shale Oil and Shale Gas Resources)

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