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Unconventional Oil and Gas: Latest Challenges and Advances of Energies

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "H1: Petroleum Engineering".

Deadline for manuscript submissions: closed (31 May 2023) | Viewed by 21249

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Dr. Junqian Li

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School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China
Interests: shale oil and gas; pore water; modeling of geo-fluids storage; reservoir characterization; gas transport
Special Issues, Collections and Topics in MDPI journals

Dr. Wenhao Li

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School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China
Interests: organic geochemistry; shale reservoir; organic matter enrichment in black shales; shale oil and gas
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Dr. Taohua He

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Guest Editor

Colleague of Resources and Environment, Yangtze University, Wuhan 430100, China
Interests: unconventional oil and gas; deep-ultra-deep oil and gas geology and exploration
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The economic development is constantly increasing the consumption of conventional oil and gas resources, causing a gap between supply and demand of oil and gas. With the progressive increase in the importance of unconventional oil and gas, research on tight oil and gas, shale oil and gas, coalbed methane, and natural gas hydrates has become of primary interest in the last decade. Storage and transport of oil and gas are the two of the most important research topics. This Special Issue aims to present papers on the latest theories and techniques in the field of unconventional oil and gas. Works pertaining to reservoir characterization, enrichment mechanisms, transport models, resource and ‘sweet spot’ evaluation of unconventional oil and gas, and geological controls of unconventional oil and gas accumulation are of particular interest for this Special Issue.

Dr. Junqian Li
Dr. Wenhao Li
Dr. Taohua He
Guest Editors

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Keywords

unconventional resources
shale oil and gas
tight oil and gas
coalbed methane
natural gas hydrate
storage and transport
resource and ‘sweet spot’ evaluation

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Published Papers (9 papers)

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Research

16 pages, 10113 KiB

Open AccessArticle

Paleoenvironment Change and Organic Matter Accumulation of Marine Shale in the Zigong Area, Southern Sichuan Basin, China: A Case Study of Well Z303

by Huimin Li, Taohua He and Weifeng Li

Energies 2023, 16(10), 4015; https://doi.org/10.3390/en16104015 - 10 May 2023

Cited by 3 | Viewed by 1396

Abstract

Marine organic-rich shale is widely distributed in the Upper Ordovician Wufeng Formation (WF-F) and Silurian Longmaxi Formation (LMX-F), making it an important target for shale gas exploration and development. In order to clarify the paleoenvironment evolution characteristics and the effect of depositional environment on organic matter (OM) accumulation of the marine shale in the Wufeng and Longmaxi Formations, a series of geochemical and petrological experiments were carried out, including TOC, Rock-Eval pyrolysis, XRD, and major and trace element analyses. Research results show that based on the variation characteristics of TOC, mineral composition, and paleoenvironment evolution characteristics, four units can be identified from bottom to top: Wufeng Formation (WF-F), Lower Longmaxi Formation (L-LMX-F), Middle Longmaxi Formation (M-LMX-F) and Upper Longmaxi Formation (U-LMX-F). The high-quality marine shale developed in WF-F and LMX-F in the Zigong area (TOC: 0.65–4.56%, avg. 2.15%) contains type I kerogen (kerogen type index: 86.0–98.3, avg. 92.7) and OM in mature stage (average of R_b and T_max are 2.94%, 646 °C, respectively). Clay minerals (avg. 42.5%) and quartz (avg. 37.7%) dominate the mineral compositions, with subordinated dolomite (avg. 6.3%), feldspar (avg. 6.0%), calcite (avg. 4.0%), and pyrite (avg. 3.5%). Paleoenvironment indicators suggest that during the sedimentary period of WF-F and L-LMX-F, the paleoclimate condition was humid; the weathering condition, paleosalinity, and redox conditions were the strongest; and there was a relatively high level of paleoproductivity and a relatively low level of terrigenous detritus influx. However, during the period of M-LMX-F and U-LMX-F, the climate gradually changed from warm and humid to hot and dry; the intensity of weathering conditions, paleosalinity, and redox conditions was relatively reduced; terrigenous detritus influx increased; and the paleoproductivity decreased. Relationships between TOC and paleoclimate condition, paleosalinity, redox condition, paleoproductivity, and terrigenous detritus influx suggest that redox condition is most important controlling factor for OM enrichment. A combination of anoxic bottom water conditions and high primary productivity and a relatively low terrigenous input resulted in the enrichment of OM in the WF-F and L-LMX-F, making it a potential exploration and development target. The research can provide scientific guidance for the selection of potential shale gas development targets in the Zigong area. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas: Latest Challenges and Advances of Energies)

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22 pages, 10568 KiB

Open AccessArticle

Well-Logging Constraints on Gas Hydrate Saturation in Unconsolidated Fine-Grained Reservoirs in the Northern South China Sea

by Xiaoming Wan, Xueqing Zhou, Jinqiang Liang, Shiguo Wu, Jingan Lu, Chenglong Wei, Rui Wang and Bo Liu

Energies 2022, 15(23), 9215; https://doi.org/10.3390/en15239215 - 5 Dec 2022

Cited by 7 | Viewed by 1672

Abstract

Recently, drilling wells have encountered rich gas hydrates in fine-grained sediments in the northern South China Sea. Gas hydrate in fine-grained sediments is very heterogeneous, and its physical properties are different from those of oil and gas reservoirs. The reliability of the classical logging saturation evaluation models established for diagenetic reservoirs is questionable. This study used four wells in GMGS3 and GMGS4 to evaluate the effects of the application of three typical methods for evaluating saturation with different principles in the unconsolidated fine-grained sediments: nuclear magnetic logging, sigma logging, and the Archie formula. It was found that the value of the lithologic capture cross-section in sigma logging and the rock’s electrical parameters in the Archie formula affect the accuracy of the model. Therefore, to obtain a reliable saturation value for fine-grained sediments, an innovative method for the calculation of resistivity and acoustic time is proposed to estimate gas hydrate saturation based on logging data, which is most consistent with the results of core analysis. The overall relative error of the verification well was 5.87%, whereas that of the density NMR logging method was 56%, showing that the accuracy of the newly proposed resistivity DT logging method’s saturation formula was significantly improved. Finally, a new model-based cross chart was developed, which can rapidly differentiate gas saturation during drilling. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas: Latest Challenges and Advances of Energies)

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14 pages, 12264 KiB

Open AccessArticle

The Advances and Challenges of the Ediacaran Fractured Reservoir Development in the Central Sichuan Basin, China

by Xiao He, Guian Guo, Qingsong Tang, Guanghui Wu, Wei Xu, Bingshan Ma, Tianjun Huang and Weizhen Tian

Energies 2022, 15(21), 8137; https://doi.org/10.3390/en15218137 - 1 Nov 2022

Cited by 8 | Viewed by 1668

Abstract

The largest Precambrian gasfield in China has been found in the central Sichuan Basin. It has been assumed as an Ediacaran (Sinian) mound–shoal, microfacies-controlled, dolomite reservoir. However, the extremely low porosity–permeability and heterogeneous reservoir cannot establish high production by conventional development technology in the deep subsurface. For this contribution, we carried out development tests on the fractured reservoir by seismic reservoir description and horizontal well drilling. New advances have been made in recent years: (1) the prestack time and depth migration processing provides better seismic data for strike-slip fault identification; (2) seismic planar strike-slip structures (e.g., en échelon/oblique faults) and lithofacies offset together with sectional vertical fault reflection and flower structure are favorable for strike–slip fault identification; (3) in addition to coherence, maximum likelihood and steerable pyramid attributes can be used to identify small strike-slip faults and for fault mapping; (4) fusion attributes of seismic illumination and structural tensor were used to find fractured reservoir along fault damage zone; (5) horizontal wells were carried out across the strike-slip fault damage zone and penetrated fractured reservoir with high production. Subsequently, a large strike-slip fault system has been found throughout the central intracratonic basin, and the “sweet spot” of the fractured reservoir along the strike-slip fault damage zone is widely developed to be a new favorable domain for high-production development. There is still a big challenge in seismic and horizontal well technology for the economical exploitation of the deep fractured reservoirs. This practice provides new insight in the deep tight matrix reservoir development. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas: Latest Challenges and Advances of Energies)

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32 pages, 11668 KiB

Open AccessArticle

Comparison of Machine Learning Algorithms for Sand Production Prediction: An Example for a Gas-Hydrate-Bearing Sand Case

by Jinze Song, Yuhao Li, Shuai Liu, Youming Xiong, Weixin Pang, Yufa He and Yaxi Mu

Energies 2022, 15(18), 6509; https://doi.org/10.3390/en15186509 - 6 Sep 2022

Cited by 7 | Viewed by 2165

Abstract

This paper demonstrates the applicability of machine learning algorithms in sand production problems with natural gas hydrate (NGH)-bearing sands, which have been regarded as a grave concern for commercialization. The sanding problem hinders the commercial exploration of NGH reservoirs. The common sand production prediction methods need assumptions for complicated mathematical derivations. The main contribution of this paper was to introduce machine learning into the prediction sand production by using data from laboratory experiments. Four main machine learning algorithms were selected, namely, K-Nearest Neighbor, Support Vector Regression, Boosting Tree, and Multi-Layer Perceptron. Training datasets for machine learning were collected from a sand production experiment. The experiment considered both the geological parameters and the sand control effect. The machine learning algorithms were mainly evaluated according to their mean absolute error and coefficient of determination. The evaluation results showed that the most accurate results under the given conditions were from the Boosting Tree algorithm, while the K-Nearest Neighbor had the worst prediction performance. Considering an ensemble prediction model, the Support Vector Regression and Multi-Layer Perceptron could also be applied for the prediction of sand production. The tuning process revealed that the Gaussian kernel was the proper kernel function for improving the prediction performance of SVR. In addition, the best parameters for both the Boosting Tree and Multi-Layer Perceptron were recommended for the accurate prediction of sand production. This paper also involved one case study to compare the prediction results of the machine learning models and classic numerical simulation, which showed the capability of machine learning of accurately predicting sand production, especially under stable pressure conditions. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas: Latest Challenges and Advances of Energies)

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12 pages, 2697 KiB

Open AccessArticle

Organic Petrological Characteristics of Graptolite and Its Contribution to Buried Organic Carbon of Longmaxi Formation Shales, Middle Yangtze Region

by Wenhao Li, Xiuzhe Wang, Min Wang and Erqiang Yang

Energies 2022, 15(7), 2520; https://doi.org/10.3390/en15072520 - 30 Mar 2022

Cited by 1 | Viewed by 1604

Abstract

The shale gas exploration of the Longmaxi Formation in the Yangtze Region of China has made a significant breakthrough. As an important hydrocarbon generation organism, graptolite is widely distributed in the Longmaxi Formation shales, but its hydrocarbon potential is still unclear. Taking the Longmaxi Formation shales in the Middle Yangtze Region as an example, this paper discusses the organic petrological characteristics of graptolite and its contribution to buried organic carbon. The Longmaxi shales in the study area can be divided into organic-rich shales (TOC > 2.0%) and organic-bearing shales (TOC < 2.0%). The organic-rich shales have high quartz content and low clay mineral content, which is opposite in the organic-bearing shales. Organic maceral results show that graptolite is widely distributed in nearly all the samples, while solid bitumen is relatively developed in organic-rich shale. The equivalent vitrinite reflectance obtained from the conversion of graptolite reflectance ranges from 2.46% to 2.76%, indicating that the organic matter maturity of the Longmaxi Formation shale is overmature. Combining an optical microscope and a field emission scanning electron microscope, the proportion of graptolite area to organic matter area can be obtained, the average of which is 32.71%. Solid bitumen mainly contributes to buried organic carbon of the organic-rich shales in the Longmaxi Formation, while graptolites contribute little to organic carbon burial. However, solid bitumen in the organic-bearing shales is relatively undeveloped, and graptolite is an important hydrocarbon generation organism, which is the main contributor to buried organic carbon. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas: Latest Challenges and Advances of Energies)

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14 pages, 4075 KiB

Open AccessArticle

Shale Reservoir Heterogeneity: A Case Study of Organic-Rich Longmaxi Shale in Southern Sichuan, China

by Hongming Zhan, Feifei Fang, Xizhe Li, Zhiming Hu and Jie Zhang

Energies 2022, 15(3), 913; https://doi.org/10.3390/en15030913 - 27 Jan 2022

Cited by 8 | Viewed by 1875

Abstract

Shale reservoir heterogeneity is strong, which seriously affects shale gas reservoir evaluation and reserves estimation. The Longmaxi Formation shale of the Luzhou block in southern Sichuan was taken as an example to characterize the pore distribution of shale over the full scale using micro-computed tomography (CT), focusing on ion beam scanning electron microscopy (FIB-SEM) and small-angle neutron scattering (SANS); further, the heterogeneity of the shale pore distribution over the full scale was explored quantitatively within different scales. The results show that shale micropores are dominated by microfractures that are mainly developed along the bedding direction and associated with organic matter, contributing 1.24% of porosity. Shale nanopores are more developed, contributing 3.57–4.72% porosity and have strong heterogeneity locally at the microscale, but the pore distribution characteristics show lateral homogeneity and vertical heterogeneity at the macroscale. In the same layer, the porosity difference is only 0.1% for the sheet samples with 2 cm adjacent to each other. Therefore, in shale core experiments in which parallel samples are needed for comparison, parallel samples should be in the same bedding position. This paper explores the extent of heterogeneity over the full scale of pore distribution from macro to micro, which has important significance for accurately characterizing the pore distribution of shale and further carrying out reservoir evaluation and estimation of reserves. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas: Latest Challenges and Advances of Energies)

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20 pages, 2937 KiB

Open AccessArticle

Geological and Engineering Integrated Shale Gas Sweet Spots Evaluation Based on Fuzzy Comprehensive Evaluation Method: A Case Study of Z Shale Gas Field HB Block

by Shiqi Liu, Yuyang Liu, Xiaowei Zhang, Wei Guo, Lixia Kang, Rongze Yu and Yuping Sun

Energies 2022, 15(2), 602; https://doi.org/10.3390/en15020602 - 14 Jan 2022

Cited by 8 | Viewed by 2100

Abstract

As an emerging unconventional energy resource, shale gas has great resource potential and developmental prospects. The effective evaluation of geological sweet spots (GSS), engineering sweet spots (ESS) and comprehensive sweet spots (CSS) is one of the main factors for a high-yield scale and economic production of shale gas. Sweet spot evaluation involves a comprehensive analysis based on multiple parameters. Conventional evaluation methods consider relatively simple or single factors. Although the main influencing factors are understood, the influence of different factors is as of yet unknown, and a comprehensive consideration may strongly affect the evaluation results. In this paper, the fuzzy mathematics method is introduced for shale gas sweet spot evaluation. With the help of fuzzy mathematics tools, such as membership function, the objective of comprehensive sweet spots evaluation based on multiple parameters is realized. Additionally, the reliability of the evaluation of sweet spots is improved. Firstly, previous research results are used for reference, and the evaluation factor system of geological and engineering sweet spots of shale gas is systematically analyzed and established. Then, the basic principle of the fuzzy comprehensive evaluation method is briefly introduced, and a geological engineering integrated shale gas sweet spots evaluation method, based on the fuzzy comprehensive evaluation method, is designed and implemented. Finally, the data from HB blocks in the Z shale gas field in China are adopted. According to the evaluation results, the modified method is tested. The results show that the method proposed in this paper can synthesize a number of evaluation indices, quickly and effectively evaluate the GSS, ESS and CSS in the target area, and the results have high rationality and accuracy, which can effectively assist in well-pattern deployment and fracture design. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas: Latest Challenges and Advances of Energies)

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22 pages, 15714 KiB

Open AccessArticle

Forecast of Economic Tight Oil and Gas Production in Permian Basin

by Wardana Saputra, Wissem Kirati and Tadeusz Patzek

Energies 2022, 15(1), 43; https://doi.org/10.3390/en15010043 - 22 Dec 2021

Cited by 8 | Viewed by 4661

Abstract

We adopt a physics-guided, data-driven method to predict the most likely future production from the largest tight oil and gas deposits in North America, the Permian Basin. We first divide the existing 53,708 horizontal hydrofractured wells into 36 spatiotemporal well cohorts based on different reservoir qualities and completion date intervals. For each cohort, we fit the Generalized Extreme Value (GEV) statistics to the annual production and calculate the means to construct historical well prototypes. Using the physical scaling method, we extrapolate these well prototypes for several more decades. Our hybrid, physico-statistical prototypes are robust enough to history-match the entire production of the Permian mudstone formations. Next, we calculate the infill potential of each sub-region of the Permian and schedule the likely future drilling programs. To evaluate the profitability of each infill scenario, we conduct a robust economic analysis. We estimate that the Permian tight reservoirs contain 54–62 billion bbl of oil and 246–285 trillion scf of natural gas. With time, Permian is poised to be not only the most important tight oil producer in the U.S., but also the most important tight gas producer, surpassing the giant Marcellus shale play. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas: Latest Challenges and Advances of Energies)

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16 pages, 6254 KiB

Open AccessArticle

Classification of Void Space Types in Fractured-Vuggy Carbonate Reservoir Using Geophysical Logging: A Case Study on the Sinian Dengying Formation of the Sichuan Basin, Southwest China

by Kunyu Wang, Juan Teng, Hucheng Deng, Meiyan Fu and Hongjiang Lu

Energies 2021, 14(16), 5087; https://doi.org/10.3390/en14165087 - 18 Aug 2021

Cited by 1 | Viewed by 2219

Abstract

The fractured-vuggy carbonate reservoirs display strong heterogeneity and need to be classified into different types for specific characterization. In this study, a total of 134 cores from six drilled wells and six outcrops of the Deng #2 and Deng #4 members of the Dengying Formation (Sichuan Basin, Southwest China) were selected to investigate the petrographic characteristics of void spaces in the fractured-vuggy carbonate reservoirs. Four void space types (VSTs) were observed, namely the solution-filling type (SFT), cement-reducing type (CRT), solution-filling breccia type (SFBT) and solution-enlarging fractures and vugs type (SEFVT). The CRT void spaces presented the largest porosity and permeability, followed by the SEFVT, SFBT and SFT. The VSTs presented various logging responses and values, and based on these, an identification method of VSTs using Bayes discriminant analysis (BDA) was proposed. Two test wells were employed for the validation of the identification method, and the results show that there is good agreement between the identification results and core description. The vertical distribution of VSTs indicates that the SFT and SEFVT are well distributed in both the Deng #2 and Deng #4 members. The CRT is mainly found in the Deng #2 member, and the SFBT occurs in the top and middle of the Deng #4 member. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas: Latest Challenges and Advances of Energies)

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