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Electrical resistivity, permeability, and normal stiffness of fractured crystalline rocks: Simultaneous laboratory measurements subjected to hydromechanical loading
Get PDFThis study presents the first simultaneous measurements of the hydraulic, electrical, and elastic properties of fractured crystalline rocks under uniaxial loading. To elucidate the fluid-related transport in hydrothermal systems based on geophysical measurements, the correlation between permeability and measurable geophysical properties should be compre-hensively understood. However, no study has investigated detailed simultaneous changes in the permeability and electrical resistivity of rough-walled fractures under hydromechanical deformation. Herein, this study simultaneously measured these properties in fractured granite and gabbro samples through laboratory experiments. During hydromechanical loading, normal stress was increased up to 50 MPa while a KCl solution was injected into void space. Resistivity was estimated based on electrical impedance and compared with permeability and fracture-specific stiffness changes under elevated stress. Consequently, increasing stress increased resistivity and stiffness for ∼ 1 decade while decreased permeability for ∼ 3 decades. The resistivity increase was lower in granite samples than that in the gabbro sample owing to lower matrix resistivity. Based on the measured matrix properties, this study estimated the electric aperture and hydraulic aperture. The ratio of electric aperture to hydraulic aperture decreased with increasing stress, reaching 0.3-0.4 at stress of > 15 MPa. These results suggest that the permeability-resistivity relationship is nonlinear and matrix effect can be insufficient at higher stress such as geothermal reservoirs. Meanwhile, the permeability-stiffness relationship might be controlled primarily by the rock type, while the resistivity-stiffness curves were regulated by the fracture surface state. These different sensitivities suggest that simultaneous measurements of the electrical and elastic properties aid in interpreting permeability changes.Document Type: Original articleCited as: Sawayama, K., So, J. Electrical resistivity, permeability, and normal stiffness of fractured crystalline rocks: Simultaneous laboratory measurements subjected to hydromechanical loading. Advances in Geo-Energy Research, 2025, 16(1): 36-49. https://doi.org/10.46690/ager.2025.04.0
Microscopic insights into CO₂-shale oil miscibility via interaction energy coupled with pore confinement: Implications for CO₂-enhanced oil recovery
Get PDFAs CO₂ injection can enhance the efficiency of shale oil extraction and reduce CO₂ emissions, it has been utilized widely in the development of shale oil resources. Minimum miscible pressure is an important parameter describing the miscibility of CO₂ and shale oil, which is of great importance for determination of CO₂ injection strategy. However, due to the unclear phase boundary caused by the confinement effect in shale nanopores, it is difficult to determine the minimum miscible pressure of CO₂ and shale oil. In this study, a new minimum miscible pressure estimation method is constructed, that is suitable for nanopores based on the significant co-evolution of pore wall adsorption and confined-bulk phase interactions. This method can mitigate the limitations of traditional minimum miscible pressure calculation methods relying on fluid interfaces. Furthermore, the confinement effects on the miscibility process are analyzed using a theoretical method and molecular dynamics simulation on the microscopic scale. The results demonstrate that the minimum miscible pressure of CO₂ and shale oil initially decreases as the pore size decreases. When the pore size decreases to a certain extent, the minimum miscible pressure increases with the thickness of the adsorbent layer rising and the CO₂ diffusion coefficient decreasing. Temperature elevation raises the minimum miscible pressure as it intensifies molecular thermal motion, weakens fluid adsorption, and reduces interaction energy, which are not conducive to miscibility. This study can provide an essential basis for the optimization of CO₂ injection pressure in shale oil reservoir development.Document Type: Original articleCited as: Yu, X., Dong, H., Li, Y., Liu, C., Zhang, L., Chen, Z. Microscopic insights into CO₂-shale oil miscibility via interaction energy coupled with pore confinement: Implications for CO₂-enhanced oil recovery. Advances in Geo-Energy Research, 2025, 17(2): 107-120. https://doi.org/10.46690/ager.2025.08.0
Multi-field coupling controls the formation and evolution of deep reservoirs
Get PDFFollowing the maturation of shallow and medium-depth exploration, the petroleum industry is transitioning its focus to deep and ultra-deep formations. Field evidence shows that, even under extreme conditions of high temperature, high pore pressure, and high stress, some reservoirs retain anomalously high porosity and permeability, contradicting traditional compaction models. This paradox can be better explained through multi-field coupling, where temperature, pore pressure, and stress interact competitively and cooperatively to reshape compaction, fracture behavior, and fluid-rock interactions. Such interactions may induce brittle–ductile transitions that form semi-ductile permeability corridors, or cause localized enrichment when stress contrasts restrict fracture propagation and fluid accumulation promotes episodic reactivation. These insights shift the interpretation of deep reservoirs from single-factor models to a coupling-based framework, offering new directions for evaluation and exploration.Document Type: PerspectiveCited as: Xu, S., Yang, D., Liu, B., Jia, C., Zhang, Y. Multi-field coupling controls the formation and evolution of deep reservoirs. Advances in Geo-Energy Research, 2025, 17(2): 176-178. https://doi.org/10.46690/ager.2025.08.0
Reactive transport modeling of water-CO₂-rock interactions in clay-coated sandstones and implications for CO₂ storage
Get PDFIn this work, the potential influences of grain-coating clays on water-CO₂-rock interactions in sandstones and subsequent ramifications for CO₂ storage were investigated using reactive transport simulations. The results indicated that, compared to pore-filling smectite, grain-coating smectite leads to significant pH decrease, increases in the CO₂-species concentrations, and decreases in smectite dissolution and the precipitation of secondary minerals. Moreover, it was revealed that smectite and chlorite coats dissolve preferentially over detrital K-feldspar being covered, while K-feldspar is dissolved preferentially over illite and kaolinite coats. While the mineral trapping mechanism is only important for smectite and chlorite coats, sandstone porosity is significantly reduced for chlorite coat but increased for the other three clay coats. The main causes of the differences between pore-filling and grain-coating scenarios for smectite and chlorite coats are ascribed to the inhibitory effect of clay coats on the growth of secondary quartz and the dissolution of clay. In addition to the above two factors, the decelerating effect of clay coats on the dissolution of K-feldspar is also important for illite coat; meanwhile, for the kaolinite coat, the dissolution of clay is less important and the other two factors are more critical. Furthermore, the coverage and thickness of clay coats, fluid flow rate, detrital grain size, detrital lithology, partial pressure of CO₂, and temperature may all impact the role of clay coats.Document Type: Original articleCited as: Li, H., Hu, Q., Zhu, R., Liu, B., Mishara, A., Ansah, E. O. Reactive transport modeling of water-CO₂-rock interactions in clay-coated sandstones and implications for CO₂ storage. Advances in Geo-Energy Research, 2025, 17(2): 121-134. https://doi.org/10.46690/ager.2025.08.0
Expansion-induced fracture propagation in deep geothermal reservoirs under alternate-temperature loading
Get PDFHydraulic fracturing is a crucial technique for the extraction of geothermal energy from hot dry rock reservoirs. However, the development of such reservoirs faces significant challenges due to the high in-situ stress and strong elastic-plastic behavior of these rocks, which often result in simplified fracture geometries and subsequent low heat extraction efficiency. To address this issue, a novel reservoir treatment method based on thermal expansion and contraction principles is proposed. By applying alternating heating-cooling treatments to the reservoir, cyclic thermal stress is generated within the rock to enhance the complexity of post-fracturing fracture networks. To investigate the resultant hydraulic fracture propagation under alternate-temperature loading, a custom-developed thick-walled cylinder expansion fracturing device was employed to study the fracture propagation mechanisms in hot dry rock samples under cyclic thermal loading. The fracture network complexity was characterized by the fractal dimension method. Experimental results demonstrated that alternate thermal load cycling significantly enhances the fracture network complexity compared to conventional single-phase heat treatment. The maximum improvement in fractal dimension (3.86% increase) was observed at 500 ◦C. Under alternating temperature loads, the upper surface fractures predominantly exhibited bilateral symmetric structures. At 600 ◦C, a substantial increase in branched fractures and rock debris near boreholes occurred, indicating that alternating temperature loads significantly enhance the complexity of engineered fracture networks in hot dry rock. These findings suggest that incorporating thermal cycling into hydraulic fracturing processes can significantly improve the fracture network complexity, thereby enhancing the efficiency of heat extraction from hot dry rock reservoirs.Document Type: Original articleCited as: Wang, D., Dong, Y., Wei, C., Zhang, Q., Sheng, M., Yu, B. Expansion-induced fracture propagation in deep geothermal reservoirs under alternate-temperature loading. Advances in Geo-Energy Research, 2025, 15(3): 261-272. https://doi.org/10.46690/ager.2025.03.0
A molecular perspective on the microscopic mechanisms of CO2 injection and water films in fluid transport and enhanced oil recovery
Get PDFMolecular dynamics simulation has emerged as a powerful tool to shed light on the fundamental mechanisms that govern fluid behavior across multiple phases, such as gas, liquid and solid, at the molecular-scale. In shale reservoirs, understanding nanoscale phenomena such as microscopic friction, oil-gas interactions during CO2 huff-n-puff processes, and the influence of co-solvents, is crucial for enhanced oil recovery and informing strategies for CO2 geological sequestration in shale. This paper explores the unique role of molecular dynamics simulations in revealing the microscopic mechanisms of fluid transport and enhanced recovery during CO2 injection, with particular attention to the effects of hydration film, CO2 affected areas and co-solvents. The regulatory mechanism of hydration films on the friction behavior of montmorillonite provides new insights into interfacial mechanics, with implications for the mobility of confined fluids. In tight reservoir systems, the microscopic oil recovery mechanisms of CO2 under varying sweep conditions water film thicknesses highlight the complexity of fluid displacement at the nanoscale. Furthermore, the co-injection of CO2 with selected co-solvents is shown to enhance both oil mobilization and carbon storage efficiency within shale nanopores, offering a promising pathway to improve recovery outcomes under diverse reservoir conditions. By providing a molecular-level understanding of these critical processes, this work lays the groundwork for bridging atomistic insights with field-scale applications for unconventional resources development.Document Type: PerspectiveCited as: Bao, J., Du, J., Zhan, S., Wang, L., Luo, Y. A molecular perspective on the microscopic mechanisms of CO2 injection and water films in fluid transport and enhanced oil recovery. Advances in Geo-Energy Research, 2025, 16(3): 288-292. https://doi.org/10.46690/ager.2025.06.0
Cross-scale analysis on shale oil initiation in nanopores: Insights into threshold pressure gradient
Get PDFThe low permeability of shale matrices necessitates overcoming a threshold pressure gradient to initiate hydrocarbon flow, which poses a major constraint on recovery efficiency. However, the microscopic mechanisms underlying the threshold pressure gradient, particularly the roles of interfacial interactions and pore confinement, remain unclear. A comprehensive understanding of the threshold pressure gradient is essential for enhancing recovery strategies and improving shale oil extraction efficiency. This study provides a comprehensive analysis of the interfacial and size effects on the threshold pressure gradient within kerogen, quartz, and portlandite pores using molecular dynamics simulations. A method for assessing molecular thermal motion and quantifying the threshold pressure gradient was developed using molecular dynamics simulations. The results indicate that the threshold pressure gradient decreases in the order of kerogen, quartz, and portlandite pores. The adsorption characteristics of shale oil components at the interface were clarified through density distribution and molecular behavior analysis, and the factors contributing to the threshold pressure gradient were identified. It was found that the threshold pressure gradient is significantly influenced by the strength of interfacial interactions between the polar shale oil components and the solid matrix. Additionally, an analytical model was proposed to predict the correlation between the threshold pressure gradient and the pore size, which can extend the prediction of the threshold pressure gradient to a larger scale of thousands of nanometers. These findings offer insights into shale oil recoverability in nanopores and provide theoretical guidance for its extraction.Document Type: Original articleCited as: Cui, F., Meng, S., Jin, X., Qian, J., Liu, H., Wu, H., Wang, F. Cross-scale analysis on shale oil initiation in nanopores: Insights into threshold pressure gradient. Advances in Geo-Energy Research, 2025, 16(2): 131-142. https://doi.org/10.46690/ager.2025.05.0
Multi-fidelity machine learning with knowledge transfer enhances geothermal energy system design and optimization
Get PDFDesigning and optimizing the control schemes of geothermal energy systems is a challenging and time-consuming work due to the vast parameter space and computationally intensive simulations. Canonical evolutionary optimization approaches are laborious, slow to converge, and may not provide optimal well-control scheme for geothermal energy systems. To tackle these issues, this work reports a machine learning-guided real-time flow control optimization for enhanced geothermal systems. This approach fully leverages existing data throughout the optimization phase by creating multi-fidelity surrogate models, which comprise coarse and fine models. The coarse model strategically selects a subset of variables to develop a low-fidelity representation, while the fine model utilizes all available variables to construct a high-fidelity surrogate. Knowledge transfer from coarse surrogate can guide the fine surrogate search into a promising subspace. Active learning technique is further leveraged to improve the accuracy of surrogate by iteratively querying the most informative data points. To evaluate effectiveness of the proposed approach, benchmark function suites and two fractured geothermal energy systems are employed in comparison with conventional evolutionary algorithms and advanced surrogate-assisted methods. The results illustrate the capability of the workflow to enhance the efficiency and effectiveness of real-time decision making. This workflow paves a new path for complex and computationally intensive design optimization problems.Document Type: Original articleCited as: Chen, G., Jiao, J. J., Wang, Z., Dai, Q. Multi-fidelity machine learning with knowledge transfer enhances geothermal energy system design and optimization. Advances in Geo-Energy Research, 2025, 16(3): 244-259. https://doi.org/10.46690/ager.2025.06.0
On multi-block lattice Boltzmann method for high Knudsen number flows
Get PDFThis work introduces a new computational framework aimed at advancing the modeling of gas transport in confined porous media, particularly shale and tight geological formations that are characterized by their intricate network of meso- and micro-scale fractures and a broad distribution of organic pores. Accurate simulation of gas behavior in such media is challenging due to the complex interactions occurring at high Knudsen numbers, where conventional continuum-based methods fail and kinetic-theory approach becomes more suitable. To tackle these complexities, this work presents a lattice Boltzmann framework tailored for large computational domains with multi-scale pore structures from nano to micro scales. This framework incorporates slip boundary conditions and features an innovative multi-block approach to enable efficient simulations over a wide range of pore sizes, from nanometers to micrometers. The novel contributions of this work include: A scale-informed grid refinement strategy, the incorporation of shear stress terms, multi-block evolution algorithm, and a novel classification method for implementing specular reflection boundary conditions on irregular surfaces. Validation against Direct Simulation Monte Carlo and Molecular Dynamics data from the literature confirms the model’s accuracy in predicting gas behavior. Simulations of methane transport in tight porous media with irregular geometries highlight the framework’s effectiveness in modeling gas permeability across varying pressure conditions. Apparent permeability results across a range of Knudsen numbers demonstrate the versatility of this framework in capturing the physics of gas transport in confined porous media.Document Type: Original articleCited as: Rustamov, N., Mostaghimi, P., Aryana, S. A. On multi-block lattice Boltzmann method for high Knudsen number flows. Advances in Geo-Energy Research, 2025, 16(2): 143-157. https://doi.org/10.46690/ager.2025.05.0
Gaseous products of organic matter thermal decomposition depending on the type of kerogen
Get PDFThe aim of the research was to ascertain the possibility of determining the type of kerogen based on gaseous products of pyrolysis of rocks containing organic matter. The relationship between the type of kerogen and the obtained gas products is important in assigning an appropriate role to the source rocks in the process of modeling petroleum systems. 13 rock samples were analyzed, representing type I, II and III kerogen, classified by the Rock Eval analysis. Thermogravimetry coupled with Fourier Transform Infrared Spectroscopy (TG-FTIR) was used for evaluation of thermal decomposition and pyrolysis gaseous products determination. It was stated that the most appropriate temperature for which gas detection should be recorded and compared is 450 and 510oC. Determining the composition of gas released in the process of pyrolysis of rocks containing organic matter, as well as the temperatures at which the maximum emission occurs allows the characterization of the type of kerogen and its maturity. FTIR spectra for rocks containing type I kerogen are characterized by the presence of a methane (CH4) peak, significant intensities of C-H stretching vibrations and the presence of C=O vibrations. During the pyrolysis of rocks containing type II kerogen, methane peaks are low, but CO2 is intensively released, and the structures of aromatic hydrocarbons disintegrate, as indicated by C=C vibrations. In the FTIR spectra of rocks representing type III kerogen, the methane (CH4) peak and C=C vibrations at temperatures of 450 and 510oC are most often absent, and the CO2 peaks are characterized by low intensity.Document Type: Original articleCited as: Labus, M., Matyasik, I. Gaseous products of organic matter thermal decomposition depending on the type of kerogen. Advances in Geo-Energy Research, 2025, 15(1): 44-54. https://doi.org/10.46690/ager.2025.01.0