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Subsurface Energy and Environmental Protection—2nd Edition

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A Special Issue of Energies (ISSN 1996-1073) belonging to the section "H: Geo-Energy".

Deadline for manuscript submissions: 31 December 2026 | Viewed by 3592

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Editors

Dr. Xiaopu Wang

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Guest Editor

School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, China
Interests: enhanced oil recovery; groundwater remediation; carbon utilization and storage; microfluidic design and applications
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Dr. Yujie Yuan

E-Mail Website
Guest Editor

School of Engineering, Edith Cowan University, Joondalup, WA 6027, Australia
Interests: shale oil/gas; natural hydrogen; underground hydrogen storage; CCUS; petroleum geology
Special Issues, Collections and Topics in MDPI journals

Dr. Naser Golsanami

E-Mail Website
Guest Editor

College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao 266590, China
Interests: geomechanics; rock mechanics; rock physics of unconventional oil and gas reservoirs; natural gas
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

As the oil and gas industry develops, certain accidents, including the 2010 Gulf of Mexico Oil Spill, are bound to occur. A large number of harmful components, such as aromatics, polyaromatic hydrocarbons (PAHs), etc., enter the surrounding environments and pose a great threat to the ecosystem and human health. Therefore, efficient remediation and treatment methods should be developed to clean the contaminants.

Besides the existing environmental problems in the oil and gas field, as the global awareness of environmental protection increases and the relative regulations and policies become stricter, there is an urgent need to improve the environmental monitoring and control during the drilling and production process and to develop environmentally friendly materials and techniques.

Furthermore, the worldwide agreement on controlling carbon emission stimulates the research and field study in CO₂-enhanced oil recovery (EOR) and sequestration, and also promotes the study of low-carbon energy resources (such as natural gas hydrates and related issues in sustainable energies, including underground hydrogen storage (UHS), geothermal exploitation, etc.).

This Special Issue focuses on topics including, but not limited to, issues listed above, and we invite authors to submit original and high-quality research and review articles addressing these issues using experimental methods, computational tools, or theoretical analysis.

Dr. Xiaopu Wang
Dr. Yujie Yuan
Dr. Naser Golsanami
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 250 words) can be sent to the Editorial Office for assessment.

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-anonymized 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

oil and gas contamination/remediation
environmental monitoring and control
environmental friendly materials and techniques in oil and gas development
environmental issues regarding the exploitation of natural gas hydrates
enhanced oil recovery (EOR)
microbial enhanced oil recovery
CO₂ enhanced oil recovery
CO₂ capture
utilization and storage (CCUS)
underground hydrogen storage (UHS)
geothermal exploitation

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Published Papers (8 papers)

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Research

27 pages, 3233 KB

Open AccessArticle

Dynamic Leakage Characteristics and Emergency Shutdown Valve Optimization for Urban High-Pressure Gas Pipelines

by Junlin Ye, Song Li, Liping Wei, Fei Wang, Dashuang Zhang and Xiaoxia Fan

Energies 2026, 19(17), 4197; https://doi.org/10.3390/en19174197 - 4 Sep 2026

Abstract

Addressing the lack of quantitative basis for dynamic response characterization and emergency shutdown decision-making in urban high-pressure gas pipeline leaks, this study takes a JS pipeline as the engineering case and establishes a dynamic simulation model based on OLGA incorporating leak and shutoff valve modules. The effects of aperture size, leak location, inlet flow rate, and valve operation on release intensity and economic losses are systematically analyzed. Results reveal that without intervention, leak-point pressure follows a four-stage evolution—steady operation, sharp drop, gradual decline to equilibrium, and post-plugging recovery—while leakage rate exhibits positively coupled synchronous behavior. Aperture size acts as an exponential-level hazard control factor; apertures ≥150 mm and rupture cases mandate immediate valve closure. Upstream leaks primarily threaten supply continuity, whereas downstream leaks exhibit sustained high-rate venting with greater release intensity, which may lead to more severe accident consequences depending on local atmospheric conditions and dispersion patterns. Inlet flow mainly modulates pressure equilibrium with limited influence on release rate. Emergency shutoff valves achieve loss reductions of 46.9–67.6% for apertures ≥150 mm, corresponding to savings of 0.47–3.48 million CNY within 4 h. These findings provide dynamic quantitative support for leak classification, coordinated valve control strategies, and emergency repair decision-making. Full article

(This article belongs to the Special Issue Subsurface Energy and Environmental Protection—2nd Edition)

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19 pages, 2002 KB

Open AccessArticle

Research on the Microscopic Residual Oil Activation Mechanism of Heavy Oil in Different Water Content Stages

by Lizhen Ge, Zongbin Liu, Yinghe Chen, Ying Jiang, Maochang Wang, Hailong Zhao, Mingxin Yang, Xiaopu Wang, Jianchun Xu and Yubo Guo

Energies 2026, 19(15), 3636; https://doi.org/10.3390/en19153636 - 3 Aug 2026

Viewed by 300

Abstract

This paper investigates the occurrence characteristics, mobilization behavior, and controlling mechanisms of microscopic remaining oil in heavy-oil systems at different water-cut stages by using a visual microfluidic platform. A series of displacement and pressure-ramping experiments were conducted at 65 °C on homogeneous and heterogeneous chips with different permeabilities and oil viscosities. Image-based saturation processing and oil-phase area recognition were further employed to quantify remaining-oil morphology, area fractions, and unit threshold pressure. Results show that, with increasing water saturation, the continuity of the oil phase deteriorates progressively, and the remaining oil evolves from cluster oil to elongated cluster oil and spot and corner-trapped oil. Accordingly, the threshold pressure increases nonlinearly, especially at high-water-cut stages. For the same water saturation, higher permeability leads to lower threshold pressure because of larger pore-throat radii and better connectivity, whereas higher viscosity raises the threshold pressure due to stronger viscous resistance. Compared with homogeneous chips, heterogeneous chips exhibit higher threshold pressure because local pore-throat bottlenecks dominate capillary resistance. The image-recognition analysis indicates that the areal fraction of cluster oil decreases continuously, while that of the discontinuous oil phase, comprising elongated cluster oil and spot and corner-trapped oil, generally increases. The unit threshold pressure of cluster oil rises monotonically, whereas that of the discontinuous oil phase first decreases and then increases, reflecting the combined effects of oil fragmentation, migration, and trapping during water flooding. Full article

(This article belongs to the Special Issue Subsurface Energy and Environmental Protection—2nd Edition)

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41 pages, 61462 KB

Open AccessArticle

Thermo-Hydro-Mechanical Modeling of Geothermal Energy Extraction Using Water and Pressurized CO₂ in Deep Reservoir Systems

by Donghuan Han, Yan Xia, Xiangyang Wang, Fansheng Ban, Xiaoxuan Li, Haoyu Diao, Yueyang Guan, Yonghan Liu, Feifei Fang and Jie Zhang

Energies 2026, 19(15), 3545; https://doi.org/10.3390/en19153545 - 28 Jul 2026

Viewed by 343

Abstract

Geothermal energy extraction using existing wellbore systems provides a promising approach for sustainable heat utilization; however, the long-term thermo-hydro-mechanical (THM) responses associated with different working fluids remain insufficiently understood. In this study, a three-dimensional coupled THM model was developed to compare geothermal heat extraction using water and pressurized CO₂ under identical geological and operational conditions. The model integrates Darcy flow, heat transfer, and linear elastic deformation to investigate the evolution of hydraulic, thermal, and mechanical fields over a 100-year operation period. The results show that the hydraulic fields rapidly reach quasi-steady states, whereas thermal responses continuously evolve due to cold-front propagation from the injection well. Compared with water, pressurized CO₂ exhibits stronger fluid mobility and produces a larger thermal influence region, resulting in different heat extraction characteristics under the same mass-flow-rate condition. Thermal cooling induces reservoir contraction and stress redistribution; however, the calculated stress and displacement variations remain within a stable range throughout the simulation period. The comparison demonstrates that pressurized CO₂ can enhance long-term thermal utilization while maintaining acceptable geomechanical stability under the investigated conditions. These findings provide insights into the selection of working fluids for wellbore-based geothermal systems and highlight the importance of coupled THM evaluation for long-term reservoir performance assessment. Full article

(This article belongs to the Special Issue Subsurface Energy and Environmental Protection—2nd Edition)

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31 pages, 11216 KB

Open AccessArticle

Design and Optimization of Bottom-Hole Temperature–Pressure Combinations in Gas Production from Gas Hydrates via Carbon Dioxide Replacement Strategy

by Jingjuan Wu, Qiang Li, Qingchao Li, Fuling Wang, Yuanfang Cheng and Chuanliang Yan

Energies 2026, 19(15), 3536; https://doi.org/10.3390/en19153536 - 27 Jul 2026

Cited by 5 | Viewed by 482

Abstract

Carbon dioxide replacement represents a promising hydrate development strategy that effectively balances production efficiency and environmental considerations. However, its production efficiency is lower than that of the depressurization strategy. This limitation can be effectively alleviated by coupling carbon dioxide replacement with inhibitor injection. The design and optimization of the temperature–pressure operating window constrain its effective implementation. In the present work, the phase equilibrium conditions of carbon dioxide hydrate and methane hydrate were experimentally investigated. It was found that the experimental values obtained in this study are in excellent agreement with those calculated by the CSMHyd program. The average absolute relative deviations (AARD) for the experimental versus calculated results are 5.77% for methane hydrate and 2.66% for carbon dioxide hydrate. Then, the methodology for determining the recommended temperature–pressure combinations used in the carbon dioxide replacement strategy was proposed, and the size of region in which these combinations occur was quantified. The investigation results found that there are significant differences in the size of the recommended region for different sea areas, and inhibitor injection reduces the size of this recommended region. Injection of 3.0 wt% NaCl solution reduces the size of recommended region from 10.968 K·MPa to 8.366 K·MPa for pure methane hydrate, and a similar trend is also observed for natural gas hydrates. Based on the experimental results, the carbon sequestration potential of natural gas hydrate development using the carbon dioxide replacement strategy on core size was analyzed. The final simulation results show that 9.05 mol of carbon dioxide hydrate was obtained in the reaction vessel, which achieves effective CO₂ sequestration. The investigation in this work provides theoretical support for dual goals of carbon sequestration and efficient gas production from gas hydrates. Full article

(This article belongs to the Special Issue Subsurface Energy and Environmental Protection—2nd Edition)

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32 pages, 33785 KB

Open AccessArticle

Heat Transfer Performance of a Multi-Branch Well System for In-Situ Conversion of Steeply Dipping Oil Shale Reservoirs

by Xingyu Liu, Guoying Wang, Jingtao Du, Huidong Zhang and Qi Fan

Energies 2026, 19(15), 3473; https://doi.org/10.3390/en19153473 - 23 Jul 2026

Viewed by 352

Abstract

Efficient heat transfer is essential for the in-situ conversion of steeply dipping oil shale reservoirs. In this study, a superheated steam-driven integrated multi-branch well system was proposed, and a coupled thermo-hydro-chemical-mass transport model considering reservoir anisotropy was established in COMSOL Multiphysics-5.6 to investigate heat transfer characteristics and evaluate the effects of key engineering parameters. The numerical model was validated through comparison with an analytical solution and previously published numerical results. The results show that superheated steam preferentially migrates through hydraulic fractures and bedding-parallel high-permeability pathways, resulting in anisotropic heat transfer. Continuous steam injection gradually forms a connected high-temperature region, and most of the reservoir exceeds 500 °C after approximately 600 days. Compared with the conventional well arrangement, the proposed well system achieves more uniform reservoir heating and enlarges the effective pyrolysis region. Parametric analysis indicates that the highest thermal performance among the investigated cases is obtained with a heating well length of 22.5 m, while increasing the inter-well angle, fracture number, and fracture width enhances heat transfer and kerogen conversion. Among the investigated cases, the configuration with three hydraulic fractures achieves the best performance, with the high-temperature region (>500 °C) exceeding 80% of the reservoir after 400 days and a cumulative hydrocarbon production of approximately 4.7 × 10⁷ mol. Sensitivity analysis further demonstrates that fracture-related parameters exert a greater influence on reservoir thermal performance than heating well length and inter-well angle. These findings provide theoretical guidance for the design and performance evaluation of integrated multi-branch well systems for the efficient in-situ conversion of steeply dipping oil shale reservoirs. Full article

(This article belongs to the Special Issue Subsurface Energy and Environmental Protection—2nd Edition)

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28 pages, 4207 KB

Open AccessArticle

Multivariate Coupling Model and Reservoir Characteristics of Enhanced Geothermal Reservoirs

by Qiang Li, Fuling Wang, Jingjuan Wu, Qingchao Li and Gan Zhang

Energies 2026, 19(13), 3180; https://doi.org/10.3390/en19133180 - 3 Jul 2026

Cited by 22 | Viewed by 791

Abstract

The reliance on a single evaluation parameter represents a major limitation in traditional geothermal reservoir assessment models, hindering accurate and effective evaluation of geothermal extraction performance. Moreover, mechanical deformation induced by cold fluid injection exerts a significant influence on both fluid flow behavior and geothermal energy recovery. In this study, a thermo-hydraulic–mechanical (THM)-coupled single-fracture model is developed based on the physical properties of the solid matrix and the seepage characteristics of the fluid, using a finite-element framework for heat and mass transfer. This model enables a multi-parameter evaluation of geothermal extraction efficiency as well as reservoir rock deformation. The simulation results indicate that reservoir temperature decreases progressively from the injection well to the production well, resulting in a gradual decline in the outlet temperature after an initial stable production period of approximately 200 days. The presence of a preferential “fastest flow path” between the injection and production wells plays a critical role in sustaining the stable production phase, whereas the development of a tongue-shaped isotherm pattern is a primary factor responsible for the reduction in outlet temperature during the later stages of extraction. In addition, thermally induced rock deformation further modifies geothermal extraction efficiency, mainly through its effects on reservoir permeability and top vertical displacement. Overall, this study provides reliable and effective fundamental data for geothermal exploitation in specific geological reservoirs, thereby supporting the role of geothermal energy as a viable supplement to fossil fuel resources. Full article

(This article belongs to the Special Issue Subsurface Energy and Environmental Protection—2nd Edition)

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13 pages, 5673 KB

Open AccessArticle

Precise Definition and Quantitative Assessment of Ineffective Boreholes in Coalbed Methane Drainage

by Ying Han, Feifan Shan, Feiyan Zhang, Chen Niu and Qingchao Li

Energies 2026, 19(11), 2681; https://doi.org/10.3390/en19112681 - 2 Jun 2026

Viewed by 314

Abstract

The efficiency of gas extraction in coalbed methane extraction is governed by coal seam permeability and borehole structural integrity. Over prolonged extraction, some boreholes become ineffective owing to degraded performance, necessitating precise identification criteria. In this study, a mathematical model for cumulative gas production under borehole failure was developed based on a gas flow decay function. Numerical analysis and data visualization were conducted via MATLAB, with mean values for collapsed/blocked boreholes adopted to eliminate the interference of unstable intervals. The analysis produced an equation that correlates the critical borehole flow rate with the time of loss of stability, providing a quantitative criterion for identifying ineffective boreholes in coal mining operations. Full article

(This article belongs to the Special Issue Subsurface Energy and Environmental Protection—2nd Edition)

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26 pages, 3404 KB

Open AccessArticle

Experimental Investigation of Permeability Sensitivity of Coal Reservoir to Reservoir Pressure and Its Fluid–Solid Coupling Control Mechanism

by Xiaokai Xu, Yue Xin, Qingchao Li, Shuo Zhang, Lin Tian and Zhengzheng Xue

Energies 2026, 19(9), 2132; https://doi.org/10.3390/en19092132 - 29 Apr 2026

Cited by 3 | Viewed by 555

Abstract

During coalbed methane (CBM) production, coal reservoir pore/fracture structure varies dynamically under the action of fluid–solid coupling. And coal reservoir permeability changes accordingly. In order to factually investigate the dynamic changes in coal reservoir permeability in the CBM well drainage process, a comparative simulation experiment on the difference in coal permeability sensitivity to confining pressure (external pressure) and pore pressure (internal pressure) was carried out in this study. The results show that coal permeability presents a typical negative exponential decline with a decrease in pore pressure. The pore pressure sensitivity experiment can effectively simulate the permeability sensitivity characteristics caused by coal reservoir pressure. Based on the negative exponential function relationship between permeability and effective stress, a new calculating method for the effective stress coefficient was deduced. Namely, its value could be expressed as the quotient of the pore pressure sensitivity curve regression coefficient divided by the confining pressure sensitivity curve regression coefficient. A dynamic theoretical model for coal reservoir permeability characterized by reservoir pressure was systematically constructed based on the unique fluid (gas/liquid)–solid coupling characteristics of coal reservoirs. Furthermore, the general characteristics of the stress sensitivity of coal permeability during coalbed methane (CBM) recovery were analyzed. The dynamic evolution characteristics of coal reservoir permeability in the study area were further examined. Taking the production and drainage data of a typical actual CBM production well as an example, the theories regarding the permeability sensitivity of coal reservoirs to reservoir pressure presented in this paper were validated in practice. This indirectly confirmed the rationality and accuracy of the calculation method for the effective stress coefficient obtained through laboratory-based permeability sensitivity simulation experiments. This research provides robust theoretical support for the systematic monitoring and prediction of fluid production, reservoir pressure, and permeability during the CBM production process, carrying significant practical implications. Full article

(This article belongs to the Special Issue Subsurface Energy and Environmental Protection—2nd Edition)

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