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A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Energy Systems".

Deadline for manuscript submissions: 30 January 2026 | Viewed by 4153

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Dr. Zhixue Sun

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School of Petroleum Engineering, China University of Petroleum, Qingdao 266580, China
Interests: quantitative characterization and geological modeling of complex oil and gas reservoirs; theory and methods of numerical simulation of complex oil and gas reservoirs; theory and simulation of EGS development
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Special Issue Information

Dear Colleagues,

This Special Issue focuses on the sustainable development of geo-energy resources in the context of the global energy transition and carbon neutrality goals, emphasizing the quantitative evaluation of geo-energy resources, integrated utilization of underground spaces (e.g., hydrogen storage, compressed air energy storage, CO₂ sequestration), and optimization of underground gas storage (UGS) systems.

This issue explores advanced technologies such as multi-physics coupling simulations, AI-driven modeling, and their applications in resource assessment, dynamic sealing integrity monitoring for UGS, and synergistic geothermal–UGS development. Interdisciplinary research integrating geoscience, engineering, and data science is encouraged, alongside innovative case studies (e.g., salt cavern gas storage, digital twin systems), to advance the efficient design of subsurface storage systems and the lifecycle management of geo-energy resources.

We would particularly like to highlight theories, methods, and key technologies for the efficient utilization of underground space, including but not limited to the following: underground gas storage (UGS), hydrogen/helium reservoirs in geological formations, strategic oil reserves in salt caverns, and the deep geological disposal of nuclear waste, all requiring interdisciplinary integration of geoscience, energy engineering, and computational analytics to address challenges in sealing integrity, thermal-fluid dynamics, and long-term stability for a sustainable energy transition and hazardous material management.

Dr. Zhixue Sun
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly 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 2400 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

geo-energy resources
quantitative evaluation
efficient development
underground space utilization
underground gas storage (UGS)
seepage flow simulation

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Published Papers (9 papers)

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Research

18 pages, 4709 KB

Open AccessArticle

Multi-Objective Optimization of Sucker Rod Pump Operating Parameters for Efficiency and Pump Life Improvement Based on Random Forest and CMA-ES

by Xiang Wang, Yuhao Zhuang, Yixin Xie, Lin Chen, Wenjie Yu, Ming Li and Ying Wu

Processes 2025, 13(12), 3871; https://doi.org/10.3390/pr13123871 - 1 Dec 2025

Viewed by 36

Abstract

The design parameters of the sucker rod pumping unit (SRPU) are influenced by multiple factors. Traditional methods based on oil production engineering theories involve numerous simplifications, making it difficult to effectively address the complex realities of oilfields, thereby requiring improvement in the reliability of pumping system design solutions. This paper, based on the massive design schemes and corresponding operational performance data accumulated during the long-term development of oilfields, innovatively proposes an intelligent optimization model combining Random Forest and Covariance Matrix Adaptation Evolution Strategy algorithm (CMA-ES). This model overcomes the shortcomings of insufficient data and incomplete design indicators in the establishment of lifting design models. By standardizing and processing the data from 5000 historical lifting scheme sets, a sample database of SRPU lifting system designs was created, covering dimensions such as well geology, fluid, and production. Based on this, aiming at system efficiency and pump life expectancy, geological development characteristic parameters and lifting design parameters were taken as variables to establish a predictive model for the operation effect of the lifting system. The dataset was divided into 8:1:1 subsets for training, hyperparameter tuning and performance testing. Subsequently, an optimization model was established to jointly optimize the lifting system design parameters. Case studies show that the intelligent optimization method can simultaneously optimize parameters such as pump setting depth, pump diameter, stroke, and frequency, with expected improvements in system efficiency of 6.75% and pump life expectancy of 29%. Full article

(This article belongs to the Special Issue Advances in Evaluation, Development, Simulation and Utilization of Geo-Energy Resources and Underground Space)

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22 pages, 33125 KB

Open AccessArticle

Identification and Distribution Prediction of Sweet Spots in Tight Reservoirs Based on Machine Learning—Taking Satan 1 Block in Jinan Depression of Junggar Basin as an Example

by Wei Zhang, Chuanyan Huang, Dianhe Xie and Junlin Chen

Processes 2025, 13(11), 3705; https://doi.org/10.3390/pr13113705 - 17 Nov 2025

Viewed by 277

Abstract

This study focuses on the tight reservoirs of the Jingzigou Formation in the Satan 1 block of the Jinan Sag, Junggar Basin. By integrating analyses of sedimentary microfacies, reservoir characteristics, and fracture distribution, it innovatively applies machine learning algorithms for the quantitative identification and prediction of “sweet spots”. The results indicate that subaqueous distributary channels within the braided river delta front are the dominant sedimentary microfacies. The reservoir exhibits typical tight oil characteristics, with porosity primarily below 10% and permeability generally less than 0.01 mD. Sedimentary microfacies significantly control reservoir quality, with the subaqueous distributary channels exhibiting the best physical properties. Mid- to high-angle structural fractures effectively enhance reservoir permeability and show a strong positive correlation with oil saturation. This research employs machine learning techniques—including Decision Trees, Random Forest, and Support Vector Machines—to establish a comprehensive sweet spot classification model by integrating pore-throat structure, petrophysical parameters, reservoir thickness, and fracture development intensity. Among these, the Random Forest algorithm demonstrated optimal performance across all evaluation metrics. Prediction results reveal that Class I and Class II sweet spots are predominantly distributed in the northern slope area, while Class III sweet spots are located in the central trough and southern nose-like structural zone. These classification results show a high consistency with actual production data, confirming the effectiveness and applicability of machine learning for sweet spot prediction in this study area. The research outcomes provide reliable geological guidance for well placement optimization and reserve development in the Satan 1 block, offering significant reference value for the prediction and development of sweet spots in similar heterogeneous tight oil reservoirs. Full article

(This article belongs to the Special Issue Advances in Evaluation, Development, Simulation and Utilization of Geo-Energy Resources and Underground Space)

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19 pages, 2593 KB

Open AccessArticle

A Ghost Wave Suppression Method for Towed Cable Data Based on the Hybrid LSMR

by Zhaoqi Wang, Ya Li, Zhixue Sun, Zhonghua Li and Dongsheng Ge

Processes 2025, 13(11), 3689; https://doi.org/10.3390/pr13113689 - 15 Nov 2025

Viewed by 243

Abstract

In marine seismic exploration, ghost waves distort reflection waveforms and narrow the frequency band of seismic records. Traditional deghosting methods are susceptible to practical limitations from sea surface fluctuations and velocity variations. This paper proposes a τ-p domain deghosting method based on the Hybrid Least Squares Residual (HyBR LSMR) algorithm. We first establish a linear forward model in the τ-p domain that describes the relationship between the total wavefield and upgoing wavefield, transforming deghosting into a linear inverse problem. The method then employs the hybrid LSMR algorithm with Tikhonov regularization to address the inherent ill-posedness. A key innovation is the integration of the Generalized Cross Validation (GCV) criterion to adaptively determine regularization parameters and iteration stopping points, effectively avoiding the semi-convergence phenomenon and enhancing solution stability. Applications to both synthetic and field data demonstrate that the proposed method effectively suppresses ghost waves under various acquisition conditions, significantly improves the signal-to-noise ratio and resolution, broadens the effective frequency band, and maintains good computational efficiency, providing a reliable solution for high-precision seismic data processing in complex marine environments. Full article

(This article belongs to the Special Issue Advances in Evaluation, Development, Simulation and Utilization of Geo-Energy Resources and Underground Space)

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18 pages, 3007 KB

Open AccessArticle

Characteristics of CO₂–Formation Water–Rock Reaction and Simulation of CO₂ Burial Efficiency in Tight Sandstone Reservoirs

by Junhong Jia, Wei Fan, Yao Lu and Ming Qu

Processes 2025, 13(11), 3644; https://doi.org/10.3390/pr13113644 - 11 Nov 2025

Viewed by 314

Abstract

To clarify the characteristics of CO₂–formation water–rock reactions in tight sandstones and their effects on CO₂-enhanced oil recovery (EOR) efficiency and storage efficiency, this study takes the tight oil reservoirs of the Changqing Jiyuan Oilfield as the research object. A variety of experimental techniques, including ICP-OES elemental analysis, powder X-ray diffraction, and scanning electron microscopy, were employed to systematically investigate the mechanisms and main influencing factors of water–rock reactions during CO₂ geological storage. The study focused on analyzing the roles of mineral composition, reservoir pore structure, and formation water chemistry in the reaction process. It explored the potential impacts of reaction products on reservoir properties. Furthermore, based on the experimental results, a coupled reservoir numerical simulation of CO₂ injection for EOR and storage was conducted to comprehensively evaluate the influence of mineralization processes on CO₂ EOR performance and long-term storage efficiency. Results show that the tight sandstone reservoirs in Jiyuan Oilfield are mainly composed of calcite, quartz, and feldspar. The dominant water–rock reactions during CO₂ formation–water interactions are calcite dissolution and feldspar dissolution. Among these, calcite dissolution is considered the controlling reaction due to its significant effect on the chemical composition of formation water, and the temporal variation in other elements shows a clear correlation with the calcite dissolution process. Further analysis reveals that water–rock reactions lead to permeability reduction in natural fractures near injection wells, thereby effectively improving CO₂ EOR efficiency, enhancing sweep volume, and increasing reservoir recovery. At the end of the EOR stage, mineralized CO₂ storage accounts for only 0.53% of the total stored CO₂. However, with the extension of time, mineralized storage gradually increases, reaching a substantial 31.08% after 500 years. The study also reveals the effects of reservoir temperature, pressure, and formation water salinity on mineralization rates, emphasizing the importance of mineral trapping for long-term CO₂ storage. These findings provide a theoretical basis and practical guidance for the joint optimization of CO₂ EOR and geological sequestration. Future research may further focus on the dynamic evolution of water–rock reactions under different geological conditions to enhance the applicability and economic viability of CO₂ storage technologies. Full article

(This article belongs to the Special Issue Advances in Evaluation, Development, Simulation and Utilization of Geo-Energy Resources and Underground Space)

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20 pages, 1688 KB

Open AccessArticle

Prediction and Operational Control of Solid Phase Production Risk in Carbonate Gas Storage Reservoirs Under Dynamic Operating Conditions

by Lihui Wang, Bo Weng, Qingguo Yin, Qi Chen, Xiaofeng Tan, Simin Zhang and Chengyun Ma

Processes 2025, 13(11), 3452; https://doi.org/10.3390/pr13113452 - 27 Oct 2025

Viewed by 270

Abstract

Underground gas storage (UGS) facilities are fundamental for national energy security and global decarbonization efforts. However, solid phase production in carbonate reservoirs, such as Qianmi Bridge, poses a significant operational challenge by compromising wellbore integrity and formation permeability. To address this, this study develops a novel, comprehensive methodology for predicting and mitigating solid phase production risk in carbonate UGS under dynamic operating conditions, specifically focusing on the Qianmi Bridge gas storage. This approach systematically integrates qualitative susceptibility assessments (using acoustic time difference, B index, and S index) with quantitative models for critical and ultimate pressure difference forecasting. Crucially, the methodology rigorously accounts for dynamic process parameters, including rock strength degradation due to acidizing, in situ stress variations, and fluid flow dynamics throughout the reservoir’s operational life cycle, a critical aspect often overlooked in conventional models designed for sandstone reservoirs. Analysis reveals that the safe operating pressure window dramatically narrows as formation pressure declines and rock strength is weakened, especially under high-intensity, multi-cycle alternating loads. Specifically, acidizing treatments can reduce the critical pressure difference by over 50% (e.g., from 40.49 MPa to 19.63 MPa), and under depleted conditions (0.6 P₀, 0.8 UCS), the reservoir’s ability to resist solid phase production approaches zero, highlighting an extremely high risk. These findings provide an essential theoretical and technical basis for formulating robust operational control strategies, enabling data-driven decision-making to enhance the long-term safety, efficiency, and overall process integrity of carbonate gas storage operations. Full article

(This article belongs to the Special Issue Advances in Evaluation, Development, Simulation and Utilization of Geo-Energy Resources and Underground Space)

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13 pages, 985 KB

Open AccessArticle

Experimental Study on the Effect of Drilling Fluid Rheological Properties on the Strength of Brittle Mud Shale

by Wei Wang, Yi Zhang, Fengke Dou, Chengyun Ma, Jianguo Chen, Tongtong Li, Hui Zhang and Wenzhen Yuan

Processes 2025, 13(10), 3059; https://doi.org/10.3390/pr13103059 - 25 Sep 2025

Viewed by 439

Abstract

To investigate the mechanism by which the rheological properties of drilling fluids affect the stability of the wellbore in brittle mud shale, this study systematically examines the influence of drilling fluids with different rheological properties on the hydration dispersion and rock strength of brittle mud shale through a series of laboratory experiments, including thermal rolling tests and uniaxial compressive strength tests on core samples. The results reveal that for weakly dispersible brittle mud shale, the rheological properties of drilling fluids have a minor effect on hydration dispersion, with rolling recovery rates consistently above 90%. However, the rheological properties of drilling fluids significantly influence the strength of brittle mud shale, and this effect is coupled with multiple factors, including rock fracture intensity index, soaking time, and confining pressure. Specifically, as the viscosity of the drilling fluid increases, the reduction in rock strength decreases; for instance, at 5 MPa confining pressure with an FII of 0.46, the strength reduction after 144 h was 69.8% in distilled water (from an initial 133.2 MPa to 40.2 MPa) compared to 36.3% with 3# drilling fluid (from 133.2 MPa to 88.7 MPa, with 100 mPa·s apparent viscosity). Both increased soaking time and confining pressure exacerbate the reduction in rock strength; a 5 MPa confining pressure, for example, caused an additional 60.9% strength reduction compared to 0 MPa for highly fractured samples (FII = 0.46) in distilled water after 144 h. Rocks with higher fracture intensity indices are more significantly affected by the rheological properties of drilling fluids. Based on the experimental results, this study proposes a strength attenuation model for brittle mud shale that considers the coupled effects of fracture intensity index, soaking time, and drilling fluid rheological properties. Additionally, the mechanism by which drilling fluid rheological properties influence the strength of brittle mud shale is analyzed, providing a theoretical basis for optimizing drilling fluid rheological parameters and enhancing the stability of wellbores in brittle mud shale formations. Full article

(This article belongs to the Special Issue Advances in Evaluation, Development, Simulation and Utilization of Geo-Energy Resources and Underground Space)

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19 pages, 4271 KB

Open AccessArticle

Experimental Study on a Coupled Plugging System of Nano-Enhanced Polymer Gel and Bridging Solids for Severe Lost Circulation

by Fuhao Bao and Lei Pu

Processes 2025, 13(9), 2751; https://doi.org/10.3390/pr13092751 - 28 Aug 2025

Viewed by 687

Abstract

With the advancement of oil and gas exploration and development technologies into deeper and ultra-deep reservoirs, complex geological conditions here render them highly susceptible to severe lost circulation. However, conventional bridging plugging methods struggle with large-sized lost circulation channels, while chemical gel plugging faces challenges such as low success rates and insufficient pressure-bearing capacity. To address this, a novel leak plugging method combining bridging and gel plugging is proposed herein. From structural stability and mechanical properties perspectives, the enhancing effect of nanomaterials on the gel system is revealed, and the synergistic mechanism of gel-bridging coupled plugging is elucidated. For the experimental setup, orthogonal experiments determined a base formulation with controllable gelation time: 10 wt% main agent, 2 wt% crosslinking agent, and a 1:3 pH regulator ratio. Introducing 1.0 wt% nanosilica enhanced gel properties, achieving 30 N strength at 120 °C aging. An optimized walnut shell bridging agent constructed the supporting skeleton, yielding a coupled plugging formulation with up to 8 MPa pressure for a 7 mm fracture. Lost circulation volume is controlled at 163 mL, outperforming single plugging methods. Research results demonstrate gel-bridging coupled plugging’s advantages for large fractures, providing new technical insights for severe lost circulation field construction. Full article

(This article belongs to the Special Issue Advances in Evaluation, Development, Simulation and Utilization of Geo-Energy Resources and Underground Space)

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12 pages, 4760 KB

Open AccessArticle

Developmental Characteristics of Post-Rift Faults and Palostress Field Inversion in the Bozhong 19-6 Structural Belt

by Shuchun Yang, Xinran Li, Ke Wang and Guidong Ping

Processes 2025, 13(9), 2726; https://doi.org/10.3390/pr13092726 - 26 Aug 2025

Viewed by 471

Abstract

The faults in the post-rift period have an important controlling effect on the migration and accumulation of oil and gas in the shallow strata of Bohai Bay Basin. Based on the seismic interpretation data of Bozhong 19-6 Structural Belt, this paper analyzes the geometric characteristics and growth history of the faults in the post-rift period and inverts the tectonic paleostress that caused the fault activities in the post-rift period. Finally, the developmental characteristics of the faults in the post-rift period are deeply understood from three aspects: fault geometry, kinematics, and dynamics. In the study area, the trend of post-rift faults are mainly east–west, followed by NEE. According to the fault activity, it can be divided into three types: newly formed faults, long-term active faults, and deep-linked faults. The latter two types are faults that existed before and then reactivated during post-rifted period. The inversion result of the Neogene is the strike-slip stress field, showing that the intermediate principal stress axis (σ₂) is oriented vertically, the minimum principal stress (σ₃) is oriented N170°, the maximum principal stress axis (σ₁) is oriented N80°, and σ₃/σ₁ = 0.24, σ₂/σ₁ = 0.62. The data used in this inversion method is easily obtained in the oil and gas industry, and the inversion results can provide an important reference for analyzing the regional tectonic evolution and clarifying the fault activity at the key moment of oil and gas accumulation. Full article

(This article belongs to the Special Issue Advances in Evaluation, Development, Simulation and Utilization of Geo-Energy Resources and Underground Space)

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24 pages, 17040 KB

Open AccessArticle

Shear-Induced Degradation and Rheological Behavior of Polymer-Flooding Waste Liquids: Experimental and Numerical Analysis

by Bingyu Sun, Hanxiang Wang, Yanxin Liu, Wei Lv, Yubao Li, Shaohua Ma, Xiaoyu Wang and Han Cao

Processes 2025, 13(9), 2677; https://doi.org/10.3390/pr13092677 - 22 Aug 2025

Viewed by 983

Abstract

Polymer flooding is an enhanced oil recovery (EOR) technique that improves oil extraction by injecting polymer solutions into reservoirs. However, the disposal and treatment of polymer flooding waste liquids (PFWL) present significant challenges due to their high viscosity, complex molecular structure, and environmental impact. This study investigates the shear-induced degradation of polymer solutions, focusing on rheological properties, particle size distribution, and morphological changes under controlled shear conditions. Experimental results show that shear forces significantly reduce the viscosity of polymer solutions, with shear rates of 4285.36 s⁻¹ in the rotating domain and 3505.21 s⁻¹ in the fixed domain. The particle size analysis reveals a significant reduction in average particle size, indicating polymer aggregate breakup. SEM images confirm these morphological changes. Additionally, numerical simulations using a power-law model highlight the correlation between shear rate, wall shear stress, and polymer degradation efficiency. This study suggests that optimizing rotor–stator configurations with high shear forces is essential for efficient polymer degradation, offering insights for designing more effective polymer waste liquid treatment systems in oilfields. Full article

(This article belongs to the Special Issue Advances in Evaluation, Development, Simulation and Utilization of Geo-Energy Resources and Underground Space)

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