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Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects: 2nd Edition

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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: 31 March 2025 | Viewed by 5061

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Special Issue Editors

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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Guest Editor

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
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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
Prof. 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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Published Papers (8 papers)

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Research

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15 pages, 3077 KiB

Open AccessArticle

Gas Content and Gas Occurrence Mechanism of Deep Coal Seams in the Shenfu-Linxing Block

by Litao Ma, Fan Yang, Jianghao Yang, Yi Cui, Wei Wang, Cheng Liu, Bo Zhang, Jiang Yang and Shu Tao

Energies 2025, 18(3), 699; https://doi.org/10.3390/en18030699 (registering DOI) - 3 Feb 2025

Abstract

The Shenfu-Linxing block in the Ordos Basin holds abundant deep coalbed methane (CBM) resources, which can alleviate gas shortages and aid dual carbon target achievement. Considering isothermal adsorption traits and parameters like vitrinite reflectance, temperature, pressure, and water saturation, a prediction model for adsorbed and free gas content was formulated. This model helps to reveal the deep CBM occurrence mechanism in the Shenfu-Linxing block. Results show that deep CBM exists in both adsorbed and free states, with adsorbed gas initially increasing then decreasing, and free gas rising then stabilizing as burial depth increases. A critical transition depth for total CBM content exists, shallowing with higher water saturation. As depth increases, temperature and pressure evolution results in a “rapid growth—slow growth—stability—slow decrease” pattern in total gas content. Adsorbed gas resides in micropores, while free gas occupies larger pores. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects: 2nd Edition)

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19 pages, 14633 KiB

Open AccessArticle

Numerical Simulation on Pore Size Multiphase Flow Law Based on Phase Field Method

by Tianjiang Wu, Changhao Yan, Ruiqi Gong, Yanhong Zhao, Xiaoyu Jiang and Liu Yang

Energies 2025, 18(1), 82; https://doi.org/10.3390/en18010082 - 28 Dec 2024

Viewed by 583

Abstract

The characteristics of CO₂ seepage in reservoirs have important research significance in the field of CCS technology application. However, the characteristics of macro-scale seepage are affected by the geometrical characteristics of micro-scale media, such as pore size and particle shape. Therefore, in this work, a series of numerical simulations were carried out using the phase field method to study the effect of pore structure simplification on micro-scale displacement process. The influences of capillary number, wettability, viscosity ratio, interfacial tension, and fracture development are discussed. The results show that the overall displacement patterns of the real pore model and the simplified particle model are almost similar, but the oil trapping mechanisms were totally different. There are differences in flow pattern, number of dominant flow channels, sensitivity to influencing factors and final recovery efficiency. The real pore model shows higher displacement efficiency. The decrease in oil wet strength of rock will change the CO₂ displacement mode from pointing to piston displacement. At the same time, the frequency of breakage will be reduced, thus improving the continuity of CO₂. When both pores and fractures are developed in the porous media, CO₂ preferentially diffuses along the fractures and has an obvious front and finger phenomenon. When CO₂ diffuses, it converges from the pore medium to the fracture and diverges from the fracture to the pore medium. The shape of fracture development in the dual medium will largely determine the CO₂ diffusion pattern. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects: 2nd Edition)

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21 pages, 7797 KiB

Open AccessArticle

The Impacts of Reservoir Heterogeneities on the CO₂-Enhanced Oil Recovery Process—A Case Study of Daqingzijing Block in Jilin Oilfield, China

by Zetang Li, Tianfu Xu, Hailong Tian and Ruosheng Pan

Energies 2024, 17(23), 6128; https://doi.org/10.3390/en17236128 - 5 Dec 2024

Viewed by 498

Abstract

With the exploitation of oilfields, the oil production efficiency of traditional water flooding has been very low, and CO₂-enhanced oil recovery (EOR) has become an inevitable trend of development. CO₂-EOR is affected by many factors, among which the heterogeneity of reservoirs is one of the main influencing factors. In order to understand the impact of different reservoir conditions on the production of oil from CO₂ and the reasons behind it, and on the basis of researching the heterogeneity of reservoir porosity and permeability and its influence on the CO₂-enhanced oil recovery process, this study has altogether established three different reservoir characteristics for comparative analysis. Under the homogeneous and heterogeneous porosity and permeability conditions of a reservoir, the displacement characteristics during a CO₂–oil displacement process were analyzed. The layered heterogenous model had the best oil displacement effect, with its oil displacement amount reaching 8.46 × 10⁴ kg, while the homogeneous model and the spatially heterogenous model had lower values; they were 1.51 × 10⁴ and 1.42 × 10⁴, respectively. The results indicate that the heterogeneous conditions overall improved the flooding effect of CO₂. Under the same injection volume and other reservoir conditions, the cumulative oil flooding effect of the layered heterogenous model was the best compared to the homogeneous and spatially heterogeneous models. Good permeability promotes the accumulation of oil, leading to a higher saturation of the oleic phase. This work provides an in-depth analysis of the effect of the non-uniform distribution of formation permeability on CO₂-enhanced oil recovery and can help to improve carbon sequestration efficiency and oil recovery in CO₂–oil recovery projects. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects: 2nd Edition)

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16 pages, 13187 KiB

Open AccessArticle

NMR-Based Investigation of Pore–Fracture Structure Heterogeneity in Deep Coals of Different Macrolithotypes in the Daning-Jixian Block, Ordos Basin

by Wei Zhang, Zheng Zhang, Liheng Bian, Rui Shi, Hewei Zhang and Jian Shen

Energies 2024, 17(23), 6081; https://doi.org/10.3390/en17236081 - 3 Dec 2024

Viewed by 504

Abstract

Deep coalbed methane (CBM) demonstrates significant production potential, and a fervent exploration and development boom is currently underway in China. The permeability of coal reservoirs is heavily influenced by pore–fracture structure heterogeneity. Some researches have been conducted on deep coals’ pore–fracture structure; however, these studies mostly consider coal as a homogeneous material, neglecting the heterogeneity of the macrolithotypes within the coal. In this study, 33 deep coals with burial depths of more than 2000 m were obtained from the Daning-Jixian block of the Ordos Basin, covering all macrolithotypes: bright coal (BC), semi-bright coal (SBC), semi-dull coal (SDC), and dull coal (DC). These samples were subjected to three sets of NMR tests in dry, fully saturated, and irreducible water conditions, with the pore–fracture structure characteristics being analyzed. The results demonstrate that the sampled deep coals’ pore–fracture structure is highly heterogeneous, with transitional pores being dominant, followed by mesopores, “macropores and fractures”, and micropores. The NMR T_2C ranges from 0.61 to 2.44 ms, with an average of 1.19 ms; a higher T_2C value indicates more developed micropores. The ranges for producible water porosity (φ_pr) and producible water saturation (S_pr) are 0.31–7.24% (avg. 2.42%) and 6.97–71.47% (avg. 31.06%), respectively. Both of them exhibit a high positive correlation with the total volumes of “macropores and fractures” and mesopores. Compared to SDC and DC, the BC and SBC, especially the former, overall contain more “macropores and fractures” and mesopores, fewer transitional pores and micropores, and higher φ_pr and S_pr. These findings suggest that regions with abundant BC and SBC should be prioritized during deep CBM exploration and production due to the inherently superior permeability and gas extraction potential of BC and SBC, and these coals are likely to require less intensive stimulation to achieve higher recovery rates and could provide more sustainable gas production over time. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects: 2nd Edition)

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16 pages, 6321 KiB

Open AccessArticle

The Prediction of Coalbed Methane Layer in Multiple Coal Seam Groups Based on an Optimized XGBoost Model

by Weiguang Zhao, Shuxun Sang, Sijie Han, Deqiang Cheng, Xiaozhi Zhou, Zhijun Guo, Fuping Zhao, Jinchao Zhang and Wei Gao

Energies 2024, 17(23), 6060; https://doi.org/10.3390/en17236060 - 2 Dec 2024

Viewed by 521

Abstract

The prediction of the optimal coalbed methane (CBM) layer plays a significant role in the efficient development of CBM in multiple coal seam groups. In this article, the XGBoost model optimized by the tree-structured Parzen estimator (TPE) algorithm was established to automatically predict the optimal CBM layer in complex multi-coal seams of the Dahebian block in Guizhou Province, China. The research results indicate that the TPE XGBoost model has higher evaluation metrics than traditional machine learning models, with higher accuracy and generalization ability. The optimal coalbed methane layer predicted by the model for the Dacong 1–3 well is the 11th coal seam. In addition, the interpretation results of the model indicate that sonic (AC) and caliper logging (CAL) are relatively important in determining the optimal CBM layer. The favorable layers for coalbed methane development are distributed in coal seams with developed fractures and high gas content. The TPE-XGBoost model can help us objectively analyze the significance of different types of logging, quickly predict the optimal layer in complex multiple coal seam groups, and greatly reduce costs and subjective impact. It provides a new approach to predict the best CBM layer in multiple coal seam groups in the Guizhou Province in the southwest of China. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects: 2nd Edition)

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15 pages, 8294 KiB

Open AccessArticle

Evidence of Microbial Activity in Coal Seam Production Water and Hydrochemical Constraints

by Yuan Bao, Xueru Chen, Zhidong Guo, Zhengyan Li, Yufei Zhuang and Min Gao

Energies 2024, 17(20), 5170; https://doi.org/10.3390/en17205170 - 17 Oct 2024

Viewed by 622

Abstract

This study aims to explore microbial activity evidence, composition of archaeal communities, and environmental constraints in coalbed-produced waters from the Hancheng Block, a representative region for coalbed methane development on the eastern margin of Ordos Basin, China. The investigation involves analyzing microbial community composition using 16S rRNA sequencing analysis as well as examining hydrogeochemical parameters. The results indicate that Euryarchaeota and Thaumarchaeota are predominant phyla within archaeal communities present in coalbed-produced water from the Hancheng Block. Among these communities, Methanobacterium is identified as the most abundant genus, followed by Methanothrix and Methanoregula. Moreover, a positive correlation is observed between the abundance of Methanobacterium and the levels of total dissolved solids as well as Mn; conversely, there is a negative correlation with dissolved organic carbon, Zn concentrations, and pH. The abundance of Co and Ni primarily influence Methanothrix while pH and Zn play significant roles in controlling Methanoregula. Additionally, No. 5 coal seam waters exhibit greater species diversity in the archaeal community compared to No. 11 counterparts. The higher abundance of archaea in the No. 5 coal seam promotes biogas generation due to the correlation between bicarbonate and dissolved inorganic carbon isotope. These research findings hold scientific significance in guiding the exploration and development of biogas within coal seams. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects: 2nd Edition)

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23 pages, 25451 KiB

Open AccessFeature PaperArticle

Impacts and Countermeasures of Present-Day Stress State and Geological Conditions on Coal Reservoir Development in Shizhuang South Block, Qinshui Basin

by Xinyang Men, Shu Tao, Shida Chen, Heng Wu and Bin Zhang

Energies 2024, 17(17), 4221; https://doi.org/10.3390/en17174221 - 23 Aug 2024

Viewed by 815

Abstract

This study investigates the reservoir physical properties, present-day stress, hydraulic fracturing, and production capacity of No. 3 coal in the Shizhuang south block, Qinshui Basin. It analyzes the control of in situ stress on permeability and hydraulic fracturing, as well as the influence of geo-engineering parameters on coalbed methane (CBM) production capacity. Presently, the direction of maximum horizontal stress is northeast–southwest, with local variations. The stress magnitude increases with burial depth, while the stress gradient decreases. The stress field of strike-slip faults is dominant and vertically continuous. The stress field of normal faults is mostly found at depths greater than 800 m, whereas the stress field of reverse faults is typically found at depths shallower than 700 m. Permeability, ranging from 0.003 to 1.08 mD, is controlled by in situ stress and coal texture, both of which vary significantly with tectonics. Hydraulic fracturing design should consider variations in stress conditions, pre-existing fractures, depth, structural trends, and coal texture, rather than employing generic schemes. At greater depths, higher pumping rates and treatment pressures are required to reduce fracture complexity and enhance proppant filling efficiency. The Shizhuang south block is divided into five zones based on in situ stress characteristics. Zones III and IV exhibit favorable geological conditions, including high porosity, permeability, and gas content. These zones also benefit from shorter gas breakthrough times, relatively higher gas breakthrough pressures, lower daily water production, and a higher ratio of critical desorption pressure to initial reservoir pressure. Tailored fracturing fluid and proppant programs are proposed for different zones to optimize subsequent CBM development. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects: 2nd Edition)

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Review

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23 pages, 5689 KiB

Open AccessReview

Research Progress on Characteristics of Marine Natural Gas Hydrate Reservoirs

by Jiajia Yan, Kefeng Yan, Ting Huang, Minghang Mao, Xiaosen Li, Zhaoyang Chen, Weixin Pang, Rui Qin and Xuke Ruan

Energies 2024, 17(17), 4431; https://doi.org/10.3390/en17174431 - 4 Sep 2024

Cited by 1 | Viewed by 966

Abstract

As one of the most important future clean energy sources, natural gas hydrate (NGH) is attracting widespread attention due to the vast reserves available and high energy density. How to extract this source in a safe, efficient, and environmentally friendly manner has become the key to the commercial utilization of its resources. This paper reviews the recent advances in the study of the fundamental reservoir properties of offshore NGH, summarizing the methods and technologies for testing the sedimentary properties of reservoirs, analyzing the characteristics in reservoir mechanics, electrics, thermodynamics, and fluid dynamics, and discusses the influence of reservoir fundamental properties on NGH exploitation. The aim is to provide guidance and reference for research on the exploitation of NGH in different target exploitation areas offshore. Full article

(This article belongs to the Special Issue Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects: 2nd Edition)

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