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Advances, challenges, and opportunities for hydraulic fracturing of deep shale gas reservoirs
Get PDFAlthough significant progress has been made in the development of shallow natural gas, the exploitation of deep shale gas continues to face numerous challenges. Therefore, conducting research on deep shale gas extraction is crucial. The efficient exploitation is contingent upon a comprehensive understanding of the mechanical properties, fracturing behaviors, and transformation processes of deep reservoir formations. This paper initially delineates the geo-mechanical characteristics and key development challenges associated with deep shale gas reservoirs. It subsequently reviews recent advancements in laboratory experiments, numerical simulations, and field technologies. Finally, suggestions and strategies are proposed to enhance the efficiency of deep shale gas development. The perspectives offered in this paper aim to provide new insights into optimizing exploration and production in deep and complex geological environments.Document Type: PerspectiveCited as: Wu, M., Chang, X., Guo, Y., Liu, J., Yang, C., Suo, Y. Advances, challenges, and opportunities for hydraulic fracturing of deep shale gas reservoirs. Advances in Geo-Energy Research, 2025, 15(1): 1-4. https://doi.org/10.46690/ager.2025.01.0
Exploring the prospects and challenges of petrophysics research from the perspective of materials physics
Get PDFRocks are the most prevalent material on solid planets, and using physical methods is the most practical and feasible way to explore planetary resources. This is also one of the most commonly used methods for oil and gas exploration on the Earth. However, many challenges remain to be addressed in practice. Based on the practice of oil and gas physical exploration, rock physicists need to answer several questions. This work aims to address these issues by exploring similarities between materials physics and petrophysics. There are some special phenomena in rock physics that can be explained by principles borrowed from materials physics. This work also examines the similarities of porous media in different physical methods, conducts comparative studies on the physical properties of porous media, and analyzes the potential for future exploration using comparative physical property methods. In addition to being applied in petroleum engineering logging and core analysis, petrophysics can also provide insights for the development of new energy and materials, offering valuable guidance for upgrading the energy structure.Document Type: PerspectiveCited as: He, J., Dang, L., Wang, L., Kang, Q., Zhang, B., Zhang, C. Exploring the prospects and challenges of petrophysics research from the perspective of materials physics. Advances in Geo-Energy Research, 2025, 16(2): 95-98. https://doi.org/10.46690/ager.2025.05.0
Multiscale modeling for multiphase flow and reactive mass transport in subsurface energy storage: A review
Get PDFModeling of multiphase flow and reactive mass transport in porous media remains a pivotal challenge in the realm of subsurface energy storage, demanding a nuanced understanding across varying scales. This review paper presents a comprehensive overview of the latest advancements in multiscale modeling techniques that address the inherent complexity of these processes. Three cutting-edge approaches are presented: hybrid multiscale simulation, which leverages both continuum and discrete modeling frameworks to enhance model fidelity; approximated physics, which simplifies complex reactions and interactions to expedite computations without significantly sacrificing accuracy; and machine-learning-assisted multiscale simulation, which integrates predictive analytics to refine simulation outputs. Each method presents distinct advantages and hurdles, collectively advancing the precision and computational efficiency of subsurface modeling. Despite the substantial progress, we recognize the persistent challenges, such as the need for more robust coupling techniques, the balance between model complexity and computational feasibility, and effectively combining machine learning with traditional physical models. Promising directions for future work are discussed to address these challenges, aiming to push the boundaries of current multiscale modeling capabilities.Document Type: Invited reviewCited as: Lyu, X., Wang, W., Voskov, D., Liu, P., Chen, L. Multiscale modeling for multiphase flow and reactive mass transport in subsurface energy storage: A review. Advances in Geo-Energy Research, 2025, 15(3): 245-260. https://doi.org/10.46690/ager.2025.03.0
Fault-controlled oil and gas reservoir unit division based on graph
Get PDFResearch on reservoir-unit division in fault-controlled oil and gas reservoirs is essential for analyzing reservoir hydrocarbon migration and accumulation. Currently, most research on reservoir-unit division has focused solely on the identification of faults and caves, employing three-dimensional spatial visualization or other methods for a simple analysis of their links. However, these approaches often lack a reasoning process that exploits the links between faults and caves for deeper insights. For such complex oil and gas reservoirs, a systematic analysis based on the interrelations between multiple geological factors is needed. Therefore, this paper proposes a graph-based method for reservoir-unit division in fault-controlled oil and gas reservoirs, enabling the representation of links between faults and caves, and it presents further systematic analysis to derive the reservoir-unit division results. A multi-attribute graph-clustering-based fault-extraction method is utilized to achieve comprehensive fault representations as fault entities. More reliable cave-instance segmentation results are obtained through attribute fusion, representing cavity entities. A graph incorporating fault and cave entities is then created. Fault entities are classified into several levels according to their spatial scale, and directed edges are utilized to represent connectivity links between faults and caves. Moreover, a connectivity analysis centered on caves was conducted using the created graph. Based on existing reservoir unit knowledge and the cave-connectivity analysis results, reservoir-unit division was achieved. The proposed method provided reservoir-unit division results highly consistent with the information contained in seismic data, offering a new perspective for multielement integrated analysis in geophysical exploration.Document Type: Original articleCited as: Zhou, C., Fei, Y., He, X., Cai, H., Yao, X., Hu, G. Fault-controlled oil and gas reservoir unit division based on graph. Advances in Geo-Energy Research, 2025, 15(1): 68-78. https://doi.org/10.46690/ager.2025.01.0
Experimental investigation of CO2 residual trapping in naturally water-wet and artificially tailored oil-wet limestones: Implications for geological CO2 storage
Get PDFAbstract:The wetting behavior of rock/CO2/brine systems highly impacts the fluid distribution at the pore-scale and multiphase flow at the macroscale and is considered a key parameter controlling the CO2 residual trapping in geological storage. The effect of wettability on residual trapping is, however, still uncertain as the current literature suggests high discrepancies among the published datasets. Moreover, the dataset for residual trapping observations for non water-wet carbonate rocks is relatively scarce; none of the published studies investigated this aspect in CO2-wet limestones. Thus, a series of core-flooding experiments was conducted at reservoir conditions for three limestone samples having different wettability states, water-wet, intermediate wet, and CO2-wet. Wettability alteration of sister rocks was achieved using stearic acid to mimic the wettability alteration in saline aquifers due to the interaction with natural organic compounds. Notably, increasing the hydrophobicity of limestone tends to decrease CO2 residual trapping efficiency ∼ 19% and 37% when the initial water-wetting state shifts to intermediate-wet and CO2-wet, respectively. This is attributed to the fluid distribution at the pore scale, in particular the wetting layers, and its effect on the CO2/brine displacement. In case of CO2-wet rocks, macroscopic CO2 wetting layers act as flow paths, which reduces the residual CO2 saturation from 29% (water-wet) to 8%. These findings advocate water-wet rocks as better candidates for CO2 residual trapping and provide insights into residual trapping-rock wettability correlation pertinent to CO2 geo-storage.Document Type: Original articleCited as: Mouallem, J., Al-Abdrabalnabi, R., Raza, A., Mahmoud, M., Isah, A., Arif, M. Experimental investigation of CO2 residual trapping in naturally water-wet and artificially tailored oil-wet limestones: Implications for geological CO2 storage. Advances in Geo-Energy Research, 2025, 17(1): 43-55. https://doi.org/10.46690/ager.2025.07.0
Pressure diagnostics in hydraulic fracturing for unconventional completion optimization
Get PDFThe accurate evaluation of hydraulic fracturing performance is essential for the iterative optimization of unconventional reservoir development. In this aspect, fracturing pressure diagnostics has been recognized as a non-invasive technique that significantly reduces operational time and cost. However, pressure-based diagnostics lack a unified workflow for the evaluation of fracture complexity and area and cannot provide sufficient guidance for design optimization. Thus, this paper proposes an integrated diagnostic framework, constructed by pressure interpretation and data mining, from which the hydraulic fracture complexity and fracture area can be quantified. The normalized fracture complexity index is defined by propagation events and energy intensity extracted from wavelet-transformed pressure signals, and the fracture area is evaluated from pressure falloff analysis. Data mining is then used to optimize the fracturing parameters based on these two indices. The results show that the proposed framework effectively characterizes the stimulated fracture area and complexity and reveals their relationships with fracturing parameters and geological factors on the basis of multi-stage data from three horizontal coalbed methane wells. The stimulated fracture area is primarily determined by the fracturing fluid volume and pumping rate, while the fracture complexity is strongly regulated by the pumping rate and compressive strength of the rock. A negative correlation was detected between the fracture complexity and the main fracture area. To balance the main area and complexity of fractures, it is necessary to optimize the key fracturing parameters. This study provides a low-cost tool that can diagnose hydraulic fracturing performance and effectively optimize unconventional completion.Document Type: Original articleCited as: Wei, Z., Sheng, M., Li, J., Zhang, B., Wang, B., Li, G. Pressure diagnostics in hydraulic fracturing for unconventional completion optimization. Advances in Geo-Energy Research, 2025, 17(3): 196-211. https://doi.org/10.46690/ager.2025.09.0
Addressing mobility control challenges in high-pressure high-temperature oil reservoirs via water-saturated CO2 injection
Get PDFThe ability of pure CO2 injection into an oil reservoir to bring about CO2 storage is hindered by the fact that CO2 is more mobile than oil. Most "mobility control" methods (such as foam injection) work only at low temperatures. This study investigates whether water-saturated CO2 injection can provide mobility control at high pressures and temperatures. In this study, CO2 and water-saturated CO2 are injected into a Bentheimer sandstone core. Experimental runs are performed at 70 ◦C to simulate a low-temperature reservoir and 116 ◦C to simulate a high-temperature reservoir. The selected pressure ranges from 10.3 to 18.6 MPa. Results show that water-saturated CO2 consistently exhibits lower mobility than pure CO2. Hence, water-saturated CO2 injection provides effective mobility control for both low- and high-temperature reservoirs, especially at higher pressure. The effectiveness of water-saturated CO2 in reducing mobility compared to pure CO2 increases exponentially with pressure. Despite the improved mobility control provided by watersaturated CO2 injection, experimental observation finds net CO2 stored and oil recovery to be similar to that of pure CO2 injection,as CO2 sweep efficiency is already high in experimental runs. However, at field-scale sweep efficiency is low. Therefore, field-scale simulations reveal a 19%-47% increase in net CO2 stored during water-saturated CO2 injection compared to pure CO2 injection.Document Type: Original articleCited as: Yin, H., Ge, J., Hussain, F. Addressing mobility control challenges in high-pressure high-temperature oil reservoirs via water-saturated CO2 injection. Advances in Geo-Energy Research, 2025, 16(3): 276-287. https://doi.org/10.46690/ager.2025.06.0
Lightening of shale oil using high-temperature supercritical CO2: An experimental study
Get PDFThis paper investigates the influence of reaction atmosphere and operation parameters of the lightening process under high temperature and high pressure on high-viscosity shale oil using an experimental approach. Two types of experiments were implemented, one involving a thermogravimetric analyzer and another using an autoclave to carry out the lightening process. By these two kinds of experiments, the effects of reaction atmosphere and operation parameters on the lightening efficiency were clarified. As for the reaction atmosphere, the effects of CO2, N2 and air were separately evaluated. As for the operation parameters, the effects of heating rate and formation rock were investigated. The results indicate that under a CO2 atmosphere, the lightening reaction is more intense than that under the other two gas phases, and it gains the highest reaction rate. Part of the minerals in the formation rock can be treated as catalyst in the shale oil lightening process. With the formation rock being present, the reaction rate increases significantly and higher contents of light components are obtained in both the lightened shale oil and gas phase. For the kinetic parameters in the lightening process, proportional relationships between the kinetic parameters and heating rates under CO2 atmosphere with and without formation rock were identified. The findings of this study can provide guidance for enhancing high-viscosity shale oil using an in-situ lightening process.Document Type: Original articleCited as: Zhou, X., Li, H., Zeng, F., Yu, C., Ouyang, H., Jiang, Q. Lightening of shale oil using high-temperature supercritical CO2: An experimental study. Advances in Geo-Energy Research, 2025, 16(2): 99-113. https://doi.org/10.46690/ager.2025.05.0
A NMR investigation of spontaneous and forced imbibition of shale under different flow and confinement conditions
Get PDFIn the development of shale gas reservoirs, hydraulic fracturing is followed by an imbibition (or soaking) stage, during which the fracturing wetting fluid migrates into the reservoir matrix. As a consequence, laboratory imbibition experiments have been performed in shale samples. However, these tests were generally conducted at atmospheric pressure and thus only involved spontaneous imbibition, which does not correspond to in-situ reservoir conditions. This study addresses this limitation by conducting forced imbibition experiments in shale samples at different flow and confinement conditions while measuring the nuclear magnetic resonance T2 relaxation spectra at regularly increasing times. It was observed that increasing the initial pressure difference between the upstream and downstream ends of the sample (hereafter called the differential pressure) significantly improved gas displacement efficiency by promoting greater water migration into the shale pore space. Moreover, it was found that decreasing the confinement (i.e., by lowering the effective pressure) further enhanced the imbibition displacement efficiency, which reaches a maximum when the effective pressure approaches zero and spontaneous imbibition occurs. Reducing the effective pressure leaded to a substantial increase in the water intake and the formation of micro-cracks, as confirmed by post-mortem scanning electron microscopy images. These results emphasize that the differential pressure and effective pressure are key factors influencing the imbibition efficiency and the related microstructural changes in shale rocks. The study highlights the importance of replicating in-situ pressure conditions in future research and provides valuable insights for optimizing gas recovery strategies in shale gas reservoirs.Document Type: Original articleCited as: Zheng, L., Jiang, J., Xiao, W., Zhu, B., Bernabé, Y., Zhang, J. A NMR investigation of spontaneous and forced imbibition of shale under different flow and confinement conditions. Capillarity, 2025, 14(2): 53-62. https://doi.org/10.46690/capi.2025.02.0
Machine learning potential insights into mechanical response and heat transfer in CO2 hydrate
Get PDFAccurate prediction of the mechanical and thermal properties of CO2 hydrates is essential for their applications in carbon sequestration and refrigeration, yet remains challenging with empirical forcefields. In this work, a deep potential machine learning potential for CO2 hydrate, trained on density functional theory datasets, is for the first time developed to serve as a unified and accurate computational framework. The as-developed deep potential machine learning potential achieves near-density functional theory accuracy in energy, force, and virial stress predictions while enabling large-scale molecular dynamics simulations at significantly reduced computational cost. Uniaxial stress-strain analyses demonstrate that the model captures the tensile strength and progressive ductile-like failure behavior. Thermal conductivity prediction agrees closely with experimental measurements within 2% deviation, outperforming empirical forcefields. Vibrational dynamics and phonon analyses reveal that the deep potential machine learning potential more accurately describes the anharmonicity and phonon scattering, especially in high-frequency modes, yielding physically realistic thermal transport behavior. This work establishes deep potential machine learning potential as a robust tool for advancing CO2 hydrate-based technologies by providing a path for accurate and efficient multi-property prediction.Document Type: Original articleCited as: Xiong, K., Li, Y., Lin, Z., Luo, G., Wu, J. Machine learning potential insights into mechanical response and heat transfer in CO2 hydrate. Advances in Geo-Energy Research, 2025, 18(1): 38-50. https://doi.org/10.46690/ager.2025.10.0