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Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects

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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 July 2024) | Viewed by 10116

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Prof. Dr. Shu Tao

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Department of Energy and Environment, School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China
Interests: exploration and development of unconventional oil and gas resources such as coalbed methane, shale gas, shale oil, oil shale, and tight sandstone gas
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Prof. Dr. Wei Ju

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School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China
Interests: reservoir geomechanics; unconventional oil and gas geology; basin analysis
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Dr. Shida Chen

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School of Energy, China University of Geosciences (Beijing), Beijing 10083, China
Interests: unconventional resource exploration and exploitation (especially for resource of deep coalbed methane)
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Dr. Zhengguang Zhang

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General Prospecting Institute of China National Administration of Coal Geology, Beijing 100039, China
Interests: coalbed methane geology; coal body structure; hydrogeochemistry; favorable area optimization; well site deployment; in-situ stress; reservoir stimulation technology; dynamic permeability
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Dr. Jiang Han

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School of Vehicle And Energy, Yanshan University, Qinhuangdao 066004, China
Interests: unconventional resource exploration and exploitation; nanofluidics and nanorobotics for enhanced oil and gas recovery
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Fossil fuels are important to both the global and Chinese economies, and “unconventional” oil and gas resources—resources that cannot be produced, transported, or refined using traditional techniques—are expected to play a larger role in helping the U.S. and China meet future energy needs. With rising energy prices, unconventional oil and gas resoures have received renewed domestic attention in recent years. The efficient exploration and development of unconventional oil and gas needs the support of a series of geological and engineering studies, including those focused on exploration, evaluation, drilling, completion, and production. The aim of this Special Issue is to introduce the latest progress in unconventional oil and gas geology and engineering, especially for reservoir evaluation, geological enrichment factors, enrichment model, permeability integrated evaluation, and mechanism analysis.

Prof. Dr. Shu Tao
Dr. Wei Ju
Dr. Shida Chen
Dr. Zhengguang Zhang
Dr. Jiang Han
Guest Editors

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Keywords

unconventional oil and gas
exploration and development
reservoir evaluation
seepage mechanism
hydrocarbon enrichment model
reservoir petrophysics

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Related Special Issue

Advances in Unconventional Oil and Gas Accumulation, Reservoir Evaluation and Seepage Mechanism in Energies (6 articles)

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Research

16 pages, 4710 KiB

Open AccessArticle

Evaluation of Favorable Fracture Area of Deep Coal Reservoirs Using a Combination of Field Joint Observation and Paleostress Numerical Simulation: A Case Study in the Linxing Area

by Shihu Zhao, Yanbin Wang, Yali Liu, Zengqin Liu, Xiang Wu, Xinjun Chen and Jiaqi Zhang

Energies 2024, 17(14), 3424; https://doi.org/10.3390/en17143424 - 11 Jul 2024

Viewed by 592

Abstract

The development of fractures under multiple geological tectonic movements affects the occurrence and efficient production of free gas in deep coal reservoirs. Taking the No.8 deep coal seam of the Benxi formation in the Linxing area as the object, a method for evaluating favorable fracture areas is established based on the combination of field joint staging, paleogeological model reconstruction under structural leveling, finite element numerical simulation, and fracture development criteria. The results show that a large number of shear fractures and fewer tensile joints are developed in the Benxi formation in the field and mainly formed in the Yanshanian and Himalayan periods. The dominant strikes of conjugate joints in the Yanshanian period are NWW (100°~140°) and NNW (150°~175°), with the maximum principal stress magnitude being 160 MPa along the NW orientation. Those in the Himalayan period are in the NNE direction (0°~40°) and the EW direction (80°~110°), with the maximum principal stress magnitude being 100 MPa along the NE orientation. The magnitudes of the maximum principal stress of the No. 8 deep coal seam in the Yanshanian period are between −55 and −82 MPa, indicative of compression; those in the Himalayan period are from −34 to −70 MPa in the compressive stress form. Areas with high shear stress values are mainly distributed in the central magmatic rock uplift, indicating the influence of magmatic rock uplift on in situ stress distribution and fracture development. Based on the comprehensive evaluation factors of fractures, the reservoir is divided into five classes and 24 favorable fracture areas. Fractures in Class I areas and Class II areas are relatively well developed and were formed under two periods of tectonic movements. The method for evaluating favorable fracture areas is not only significant for the prediction of fractures and free gas contents in this deep coal reservoir but also has certain reference value for other reservoirs. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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12 pages, 4712 KiB

Open AccessArticle

Experimental Evaluation of Enhanced Oil Recovery in Shale Reservoirs Using Different Media

by Jiaping Tao, Siwei Meng, Dongxu Li, Lihao Liang and He Liu

Energies 2024, 17(14), 3410; https://doi.org/10.3390/en17143410 - 11 Jul 2024

Viewed by 629

Abstract

The presence of highly developed micro-nano pores and poor pore connectivity constrains the development of shale oil. Given the rapid decline in oil production , enhanced oil recovery (EOR) technologies are necessary for shale oil development. The shale oil reservoirs in China are mainly continental and characterized by high heterogeneity, low overall maturity, and inferior crude oil quality. Therefore, it is more challenging to achieve a desirably high recovery factor. The Qingshankou Formation is a typical continental shale oil reservoir, with high clay content and well-developed bedding. This paper introduced high-precision non-destructive nuclear magnetic resonance technology to carry out a systematic and targeted study. The EOR performances and oil recovery factors related to different pore sizes were quantified to identify the most suitable method. The results show that surfactant, CH₄, and CO₂ can recover oil effectively in the first cycle. As the huff-and-puff process continues, the oil saturated in the shale gradually decreases, and the EOR performance of the surfactant and CH₄ is considerably degraded. Meanwhile, CO₂ can efficiently recover oil in small pores (<50 nm) and maintain good EOR performance in the second and third cycles. After four huff-and-puff cycles, the average oil recovery of CO₂ is 38.22%, which is much higher than that of surfactant (29.82%) and CH₄ (19.36%). CO₂ is the most applicable medium of the three to enhance shale oil recovery in the Qingshankou Formation. Additionally, the injection pressure of surfactant increased the fastest in the injection process, showing a low flowability in nano-pores. Thus, in the actual shale oil formations, the swept volume of surfactant will be suppressed, and the actual EOR performance of the surfactant may be limited. The findings of this paper can provide theoretical support for the efficient development of continental shale oil reservoirs. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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18 pages, 3430 KiB

Open AccessArticle

Experimental Study of Forced Imbibition in Tight Reservoirs Based on Nuclear Magnetic Resonance under High-Pressure Conditions

by Xiaoshan Li, Liu Yang, Dezhi Sun, Bingjian Ling and Suling Wang

Energies 2024, 17(12), 2993; https://doi.org/10.3390/en17122993 - 18 Jun 2024

Viewed by 547

Abstract

This study utilizes nuclear magnetic resonance (NMR) techniques to monitor complex microstructures and fluid transport, systematically examining fluid distribution and migration during pressure imbibition. The results indicate that increased applied pressure primarily affects micropores and small pores during the initial imbibition stage, enhancing the overall imbibition rate and oil recovery. Higher capillary pressure in the pores strengthens the imbibition ability, with water initially displacing oil from smaller pores. Natural microfractures allow water to preferentially enter and displace oil, thereby reducing oil recovery from these pores. Additionally, clay minerals may induce fracture expansion, facilitating oil flow into the expanding space. This study provides new insights into fluid distribution and migration during pressure imbibition, offering implications for improved oil production in tight reservoirs. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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20 pages, 4174 KiB

Open AccessFeature PaperArticle

Occurrence and Potential for Coalbed Methane Extraction in the Depocenter Area of the Upper Silesian Coal Basin (Poland) in the Context of Selected Geological Factors

by Sławomir Kędzior and Lesław Teper

Energies 2024, 17(11), 2592; https://doi.org/10.3390/en17112592 - 28 May 2024

Viewed by 597

Abstract

Coalbed methane (CBM) is the only unconventional gas in Poland with estimated recoverable resources. The prospects for developing deep CBM have been explored in recent years by drilling deep exploration wells within the depocenter of the Upper Silesian Coal Basin. The purpose of this study is to analyze the occurrence and potential for CBM extraction in this area of the basin, which can be considered prospective due to the confirmed presence of significant amounts of gas and thick coal seams at depths > 1500 m. The study examined the vertical and horizontal variability of the gas content in the studied area, the coal rank in the seams, thermal conditions, and coal reservoir parameters. The gas content in the seams, reaching more than 18 m³/t coal^daf at a depth of 2840 m, and indicative estimated gas resources of 9 billion m³ were found. The high gas content is accompanied by positive thermal and coal rank anomalies. The permeability and methane saturation of the coal seams are low, and therefore, potential methane production may prove problematic. However, the development of CBM extraction technologies involving directional drilling with artificial fracturing may encourage gas production testing in the study area. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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16 pages, 35215 KiB

Open AccessArticle

Hydrocarbon Accumulation Process and Mode in Proterozoic Reservoir of Western Depression in Liaohe Basin, Northeast China: A Case Study of the Shuguang Oil Reservoir

by Guangjie Zhao, Fujie Jiang, Qiang Zhang, Hong Pang, Shipeng Zhang, Xingzhou Liu and Di Chen

Energies 2024, 17(11), 2583; https://doi.org/10.3390/en17112583 - 27 May 2024

Viewed by 551

Abstract

The Shuguang area has great oil and gas potential in the Proterozoic and it is a major exploration target in the Western Depression. However, controlling factors and a reservoir-forming model of the Shuguang reservoir need further development. The characteristics of the reservoir formation in this area were discussed by means of a geochemical technique, and the controlling factors of the oil reservoir were summarized. The oil generation intensity of Es4 source rock was 25 × 10⁶–500 × 10⁶ t/km², indicating that the source rocks could provide enough oil for the reservoir. The physical property of the quartz sandstone reservoir was improved by fractures and faults, which provided a good condition for the oil reservoir. Two periods of oil charging existed in the reservoir, with peaks of 38 Ma and 28 Ma, respectively. A continuous discharge of oil is favorable for oil accumulation. Oil could migrate through faults and fractures. In addition, the conditions of source–reservoir–cap assemblage in the Shuguang area well preserved the oil reservoir. The lower part of the Shuguang reservoir was source rock, the upper part was reservoir, and it was a structure-lithologic oil reservoir. These results are crucial for further oil exploration. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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20 pages, 3556 KiB

Open AccessFeature PaperArticle

Solvent Exsolution and Liberation from Different Heavy Oil–Solvent Systems in Bulk Phases and Porous Media: A Comparison Study

by Wei Zou and Yongan Gu

Energies 2024, 17(10), 2287; https://doi.org/10.3390/en17102287 - 9 May 2024

Viewed by 734

Abstract

In this paper, experimental and numerical studies were conducted to differentiate solvent exsolution and liberation processes from different heavy oil–solvent systems in bulk phases and porous media. Experimentally, two series of constant-composition-expansion (CCE) tests in a PVT cell and differential fluid production (DFP) tests in a sandpacked model were performed and compared in the heavy oil–CO₂, heavy oil–CH₄, and heavy oil–C₃H₈ systems. The experimental results showed that the solvent exsolution from each heavy oil–solvent system in the porous media occurred at a higher pressure. The measured bubble-nucleation pressures (P_n) of the heavy oil–CO₂ system, heavy oil–CH₄ system, and heavy oil–C₃H₈ system in the porous media were 0.24 MPa, 0.90 MPa, and 0.02 MPa higher than those in the bulk phases, respectively. In addition, the nucleation of CH₄ bubbles was found to be more instantaneous than that of CO₂ or C₃H₈ bubbles. Numerically, a robust kinetic reaction model in the commercial CMG-STARS module was utilized to simulate the gas exsolution and liberation processes of the CCE and DFP tests. The respective reaction frequency factors for gas exsolution (rff_e) and liberation (rff_l) were obtained in the numerical simulations. Higher values of rff_e were found for the tests in the porous media in comparison with those in the bulk phases, suggesting that the presence of the porous media facilitated the gas exsolution. The magnitudes of rff_e for the three different heavy oil–solvent systems followed the order of CO₂ > CH₄ > C₃H₈ in the bulk phases and CH₄ > CO₂ > C₃H₈ in the porous media. Hence, CO₂ was exsolved from the heavy oil most readily in the bulk phases, whereas CH₄ was exsolved from the heavy oil most easily in the porous media. Among the three solvents, CH₄ was also found most difficult to be liberated from the heavy oil in the DFP test with the lowest rff_l of 0.00019 min⁻¹. This study indicates that foamy-oil evolution processes in the heavy oil reservoirs are rather different from those observed from the bulk-phase tests, such as the PVT tests. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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23 pages, 6356 KiB

Open AccessArticle

Influence of Organic Matter Thermal Maturity on Rare Earth Element Distribution: A Study of Middle Devonian Black Shales from the Appalachian Basin, USA

by Shailee Bhattacharya, Shikha Sharma, Vikas Agrawal, Michael C. Dix, Giovanni Zanoni, Justin E. Birdwell, Albert S. Wylie, Jr. and Tom Wagner

Energies 2024, 17(9), 2107; https://doi.org/10.3390/en17092107 - 28 Apr 2024

Viewed by 1034

Abstract

This study focuses on understanding the association of rare earth elements (REE; lanthanides + yttrium + scandium) with organic matter from the Middle Devonian black shales of the Appalachian Basin. Developing a better understanding of the role of organic matter (OM) and thermal maturity in REE partitioning may help improve current geochemical models of REE enrichment in a wide range of black shales. We studied relationships between whole rock REE content and total organic carbon (TOC) and compared the correlations with a suite of global oil shales that contain TOC as high as 60 wt.%. The sequential leaching of the Appalachian shale samples was conducted to evaluate the REE content associated with carbonates, Fe–Mn oxyhydroxides, sulfides, and organics. Finally, the residue from the leaching experiment was analyzed to assess the mineralogical changes and REE extraction efficiency. Our results show that heavier REE (HREE) have a positive correlation with TOC in our Appalachian core samples. However, data from the global oil shales display an opposite trend. We propose that although TOC controls REE enrichment, thermal maturation likely plays a critical role in HREE partitioning into refractory organic phases, such as pyrobitumen. The REE inventory from a core in the Appalachian Basin shows that (1) the total REE ranges between 180 and 270 ppm and the OM-rich samples tend to contain more REE than the calcareous shales; (2) there is a relatively higher abundance of middle REE (MREE) to HREE than lighter REE (LREE); (3) there is a disproportionate increase in Y and Tb with TOC likely due to the rocks being over-mature; and (4) the REE extraction demonstrates that although the OM has higher HREE concentration, the organic leachates contain more LREE, suggesting it is more challenging to extract HREE from OM than using traditional leaching techniques. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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22 pages, 6209 KiB

Open AccessArticle

Study on Sedimentary Environment and Organic Matter Enrichment Model of Carboniferous–Permian Marine–Continental Transitional Shale in Northern Margin of North China Basin

by Hanyu Zhang, Yang Wang, Haoran Chen, Yanming Zhu, Jinghui Yang, Yunsheng Zhang, Kailong Dou and Zhixuan Wang

Energies 2024, 17(7), 1780; https://doi.org/10.3390/en17071780 - 8 Apr 2024

Cited by 2 | Viewed by 698

Abstract

The shales of the Taiyuan Formation and Shanxi Formation in the North China Basin have good prospects for shale gas exploration and development. In this study, Well KP1 at the northern margin of the North China Basin was used as the research object for rock mineral, organic geochemical, and elemental geochemical analyses. The results show that brittle minerals in the shales of the Taiyuan Formation and Shanxi Formation are relatively rare (<40%) and that the clay mineral content is high (>50%). The average TOC content is 3.68%. The organic matter is mainly mixed and sapropelic. The source rocks of the Taiyuan Formation and Shanxi Formation are mainly felsic, and the tectonic background lies in the continental island arc area. The primary variables that influenced the enrichment of organic materials during the sedimentary stage of the Taiyuan Formation were paleosalinity and paleoproductivity. Paleosalinity acted as the primary regulator of organic matter enrichment during the sedimentary stage of the Shanxi Formation. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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20 pages, 5403 KiB

Open AccessArticle

Intelligent Identification Method for the Diagenetic Facies of Tight Oil Reservoirs Based on Hybrid Intelligence—A Case Study of Fuyu Reservoir in Sanzhao Sag of Songliao Basin

by Tao Liu, Zongbao Liu, Kejia Zhang, Chunsheng Li, Yan Zhang, Zihao Mu, Fang Liu, Xiaowen Liu, Mengning Mu and Shiqi Zhang

Energies 2024, 17(7), 1708; https://doi.org/10.3390/en17071708 - 3 Apr 2024

Viewed by 770

Abstract

The diagenetic facies of tight oil reservoirs reflect the diagenetic characteristics and micro-pore structure of reservoirs, determining the formation and distribution of sweet spot zones. By establishing the correlation between diagenetic facies and logging curves, we can effectively identify the vertical variation of diagenetic facies types and predict the spatial variation of reservoir quality. However, it is still challenging work to establish the correlation between logging and diagenetic facies, and there are some problems such as low accuracy, high time consumption and high cost. To this end, we propose a lithofacies identification method for tight oil reservoirs based on hybrid intelligence using the Fuyu oil layer of the Sanzhao depression in Songliao Basin as the target area. Firstly, the geological characteristics of the selected area were analyzed, the definition and classification scheme of diagenetic facies and the dominant diagenetic facies were discussed, and the logging response characteristics of various diagenetic facies were summarized. Secondly, based on the standardization of logging curves, the logging image data set of various diagenetic facies was built, and the imbalanced data set processing was performed. Thirdly, by integrating CNN (Convolutional Neural Networks) and ViT (Visual Transformer), the C-ViTM hybrid intelligent model was constructed to identify the diagenetic facies of tight oil reservoirs. Finally, the effectiveness of the method is demonstrated through experiments with different thicknesses, accuracy and single-well identification. The experimental results show that the C-ViTM method has the best identification effect at the sample thickness of 0.5 m, with Precision of above 86%, Recall of above 90% and F1 score of above 89%. The calculation result of the Jaccard index in the identification of a single well was 0.79, and the diagenetic facies of tight reservoirs can be identified efficiently and accurately. At the same time, it also provides a new idea for the identification of the diagenetic facies of old oilfields with only logging image data sets. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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18 pages, 10301 KiB

Open AccessArticle

Numerical Simulation Study on the Influence of Cracks in a Full-Size Core on the Resistivity Measurement Response

by Hanwen Zheng, Zhansong Zhang, Jianhong Guo, Sinan Fang and Can Wang

Energies 2024, 17(6), 1386; https://doi.org/10.3390/en17061386 - 13 Mar 2024

Viewed by 720

Abstract

The development of fractured oil fields poses a formidable challenge due to the intricate nature of fracture development and distribution. Fractures profoundly impact core resistivity, making it crucial to investigate the mechanism behind the resistivity response change in fracture cores. In this study, we employed the theory of a stable current field to perform a numerical simulation of the resistivity response of single-fracture and complex-fracture granite cores, using a full-size granite core with cracks as the model. We considered multiple parameters of the fracture itself and the formation to explore the resistivity response change mechanism of the fracture core. Our findings indicate that, in the case of a core with a single fracture, the angle, width, and length of the fracture (fracture occurrence) significantly affect core resistivity. When two fractures run parallel for a core with complex fractures, the change law of core resistivity is similar to that of a single fracture. However, if two fractures intersect, the relative position of the two fractures becomes a significant factor in addition to the width and length of the fracture. Interestingly, a 90° difference exists between the change law of core resistivity and the change law of the resistivity logging response. Furthermore, the core resistivity is affected by matrix resistivity and the resistivity of the mud filtrate, which emphasizes the need to calibrate the fracture dip angle calculated using dual laterolog resistivity with actual core data or special logging data in reservoirs with different geological backgrounds. In the face of multiple fractures, the dual laterolog method has multiple solutions. Our work provides a reference and theoretical basis for interpreting oil and gas in fractured reservoirs based on logging data and holds significant engineering guiding significance. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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15 pages, 5131 KiB

Open AccessArticle

Evaluation of Grain Size Effects on Porosity, Permeability, and Pore Size Distribution of Carbonate Rocks Using Nuclear Magnetic Resonance Technology

by Shutong Wang, Yanhai Chang, Zefan Wang and Xiaoxiao Sun

Energies 2024, 17(6), 1370; https://doi.org/10.3390/en17061370 - 13 Mar 2024

Viewed by 929

Abstract

Core analysis is an accurate and direct method for finding the physical properties of oil and natural gas reservoirs. However, in some cases coring is time consuming and difficult, and only cuttings with the drilling fluid can be obtained. It is important to determine whether cuttings can adequately represent formation properties such as porosity, permeability, and pore size distribution (PSD). In this study, seven limestone samples with different sizes were selected (Cubes: 4 × 4 × 4 cm, 4 × 4 × 2 cm, 4 × 2 × 2 cm and 2 × 2 × 2 cm, Core: diameter of 2.5 cm and a length of 5 cm, Cuttings: 1–1.7 mm and 4.7–6.75 mm in diameter), and low-field nuclear magnetic resonance (NMR) measurements were performed on these samples to obtain porosity, PSD, and permeability. The results showed that the porosity of cubes and cuttings with different sizes are consistent with cores, which is about 1%. Whereas the PSDs and permeabilities of the two cutting samples (less than in size 6.75 mm) differ significantly within cores. It is suggested that interparticle voids and mechanical pulverization during sample preparation have a negligible effect on porosity and a larger effect on PSD and permeability. Combined with factors such as wellbore collapse and mud contamination suffered in the field, it is not recommended to use cuttings with a particle size of less than 6.75 mm to characterize actual extra-low porosity and extra-low permeability formation properties. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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22 pages, 19611 KiB

Open AccessArticle

Geological Constraints on the Gas-Bearing Properties in High-Rank Coal: A Case Study of the Upper Permian Longtan Formation from the Songzao Coalfield, Chongqing, Southwest China

by Dishu Chen, Jinxi Wang, Xuesong Tian, Dongxin Guo, Yuelei Zhang and Chunlin Zeng

Energies 2024, 17(5), 1262; https://doi.org/10.3390/en17051262 - 6 Mar 2024

Viewed by 981

Abstract

The Permian Longtan Formation in the Songzao coalfield, Southwest China, has abundant coalbed methane (CBM) stored in high-rank coals. However, few studies have been performed on the mechanism underlying the differences in CBM gas content in high-rank coal. This study focuses on the characterization of coal geochemical, reservoir physical, and gas-bearing properties in the coal seams M₆, M₇, M₈, and M₁₂ based on the CBM wells and coal exploration boreholes, discusses the effects of depositional environment, tectono-thermal evolution, and regional geological structure associated with CBM, and identifies major geological constraints on the gas-bearing properties in high-rank coal. The results show that high-rank coals are characterized by high TOC contents (31.49~51.32 wt%), high T_max and R₀ values (averaging 539 °C and 2.17%), low HI values (averaging 15.21 mg of HC/g TOC), high porosity and low permeability, and high gas-bearing contents, indicating a post-thermal maturity and a good CBM production potential. Changes in the shallow bay–tidal flat–lagoon environment triggered coal formation and provided the material basis for CBM generation. Multistage tectono-thermal evolution caused by the Emeishan mantle plume activity guaranteed the temperature and time for overmaturation and thermal metamorphism and added massive pyrolytic CBM, which improved the gas production potential. Good geological structural conditions, like enclosed fold regions, were shown to directly control CBM accumulation. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects)

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