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A critical review of capillary pressure behavior and characterization in fractional-wet reservoirs
Get PDFFractional wettability is common in oil and gas reservoirs, resulting in complex fluid distribution and transport phenomena. A precise understanding of capillary pressure behavior and characterization in fractional-wet reservoirs, including the two-phase flow mechanisms within pores and relationship between capillary pressure and saturation in porous media, is significant to enhanced oil recovery strategies. In this paper, an in-depth review of the two-phase flow mechanisms in fractional-wet pores and capillary entry pressures in various displacement processes was conducted. Furthermore, the effects of oil-wet proportion and contact angle on capillary pressure characterization were summarized, highlighting the emergence of similar capillary pressure curves under conditions of low oil-wet proportions. The prediction models for capillary pressure, containing empirical equations and physics-based models were discussed, with the aim of clarifying the most effective prediction methodologies. Finally, the review was finalized by outlining key findings and future directions for both experimental and theoretical studies in the realm of capillary pressure behavior and characterization.Document Type: Invited reviewCited as: Xiao, Y., You, Z., Wang, L., Du, Z. A critical review of capillary pressure behavior and characterization in fractional-wet reservoirs. Capillarity, 2024, 10(1): 12-21. https://doi.org/10.46690/capi.2024.01.0
Enhancement of oil transport through nanopores via cation exchange in thin brine films at rock-oil interface
Get PDFInteractions at the oil/brine/rock interfaces play a pivotal role in the mobility of crude oil within reservoir matrices. Unraveling the microscopic mechanisms of these interactions is crucial for ion-engineered water flooding in secondary and tertiary oil recovery. In this study, the occurrence and transport behavior of crude oil in kaolinite nanopores covered with thin brine films was investigated by molecular dynamics simulation. There is an apparent interface layered phenomenon for the liquid molecules in slit pores and the polar oil components primarily concentrate at the oil/brine interfacial region and form various binding connections with ions. The interfacial interactions between the polar oil components and brine ions exhibit an inhibitory effect on the transport of crude oil through nanopores. The interaction mechanism between acetic acid molecules and hydrated ions was elucidated by interaction modes and interaction intensity, which was proved to illustrate the flow difference in different brine film systems. Moreover, a strategy of exchanging the binding sites of divalent cations with acetic acid molecules by monovalent cations with a higher concentration was proposed. The cation exchange scheme was further validated, demonstrating an enhancement in the oil mobility within nanopores. These findings deepen our understanding of oil/brine/rock interfacial interactions and provide a significant molecular perspective on ion-engineered water flooding for enhanced oil recovery.Document Type: Original articleCited as: Hong, X., Jin, X., Shen, M., Fan, J., Wu, H., Wang, F. Enhancement of oil transport through nanopores via cation exchange in thin brine films at rock-oil interface. Advances in Geo-Energy Research, 2024, 12(1): 22-34. https://doi.org/10.46690/ager.2024.04.0
On the frequency-dependent attenuation in low-frequency mechanical testing of rock samples
Get PDFIn forced-oscillation mechanical testing of rock samples, low-frequency attenuation is traditionally measured by the tangent of the strain-stress phase lag, which is interpreted as the frequency-dependent inverse quality factor. However, such phenomenological parameter only refers to harmonic waves in a homogeneous medium, lacking physical meaning in heterogeneous media or for finite bodies. It depends on specific boundary conditions and becomes insufficient for characterizing fluid-saturated porous rock. It is also sensitive to geometrical spreading, which is poorly known but can be significant in forcedoscillation experiments. To overcome these limitations and uncertainties of quality factor, one can use the temporal attenuation coefficient, a more fundamental quantity directly representing the relative mechanical-energy dissipation rate within the medium. Here, frequency-dependent attenuation coefficient is formulated from calibration experiments with Plexiglas and several published forced-oscillation measurements with fluid-containing porous rocks at variable temperatures. The resulting attenuation coefficient, unlike the quality factor, reveals important attenuation attributes: Effective geometrical attenuation, effective attenuation, relaxation time, and effective viscosity. The effective attenuation is related to the presence of pore fluids or melts, increases with temperature, and decreases with static pressure and pore-fluid viscosity. The effective geometrical attenuation is small in experiments with sandstone but becomes significant in high-temperature, torsional-deformation experiments with olivine aggregates. Unlike the inverse quality factor, the peak in the residual attenuation coefficient yields additional quantitative parameters to characterize the elasticity and internal friction within the rock. This work provides a new way for studying seismic attenuation, which shall be helpful to oil and gas exploration.Document Type: Original articleCite as: Deng, W., Morozov, I. B., Fu, L.-Y. On the frequency-dependent attenuation in low-frequency mechanical testing of rock samples. Advances in Geo-Energy Research, 2024, 12(3): 223-236. https://doi.org/10.46690/ager.2024.06.0
Stable diffusion for high-quality image reconstruction in digital rock analysis
Get PDFDigital rock analysis is a promising approach for visualizing geological microstructures and understanding transport mechanisms for underground geo-energy resources exploitation. Accurate image reconstruction methods are vital for capturing the diverse features and variability in digital rock samples. Stable diffusion, a cutting-edge artificial intelligence model, has revolutionized computer vision by creating realistic images. However, its application in digital rock analysis is still emerging. This study explores the applications of stable diffusion in digital rock analysis, including enhancing image resolution, improving quality with denoising and deblurring, segmenting images, filling missing sections, extending images with outpainting, and reconstructing three-dimensional rocks from two-dimensional images. The powerful image generation capability of diffusion models shed light on digital rock analysis, showing potential in filling missing parts of rock images, lithologic discrimination, and generating network parameters. In addition, limitations in existing stable diffusion models are also discussed, including the lack of real digital rock images, and not being able to fully understand the mechanisms behind physical processes. Therefore, it is suggested to develop new models tailored to digital rock images for further progress. In sum, the integration of stable diffusion into digital core analysis presents immense research opportunities and holds the potential to transform the field, ushering in groundbreaking advances.Document Type: Original articleCited as: Ma, Y., Liao, Q., Yan, Z., You, S., Song, X., Tian, S., Li, G. Stable diffusion for high-quality image reconstruction in digital rock analysis. Advances in Geo-Energy Research, 2024, 12(3): 168-182. https://doi.org/10.46690/ager.2024.06.0
Progress and prospects of mining disaster prevention techniques and equipment
Get PDFAs mining operations delve deeper and mechanization and intelligence levels improve, coal mine disasters are becoming increasingly severe. Consequently, developing effective technology and equipment is crucial to ensure the safety of mining enterprises. This perspective summarizes the technical methods for preventing coal and rock dynamic disasters and controlling dust in coal mines. Furthermore, it provides insights into the future directions of mining disaster prevention techniques and equipment in this field. The aim of this paper is to offer effective disaster prevention strategies, enhance the efficiency and effectiveness of disaster control, and further safeguard the health and safety of miners.Document Type: PerspectiveCited as: He, S., Zhao, D., Gao, N., Nie, W., Tong, L., Wang, C. Progress and prospects of mining disaster prevention techniques and equipment. Advances in Geo-Energy Research, 2024, 13(3): 166-168. https://doi.org/10.46690/ager.2024.09.0
Small angle neutron scattering studies of shale oil occurrence status at nanopores
Get PDFUtilizing small angle neutron scattering techniques on organic shales, this study presents an innovative approach for characterizing the status of oil occurrence, and new insights into pore scale assessment through scattering vector-pore size relationship. The results indicate the successful identification of different shale oil occurrence status, before and after solvent extraction of residual oil for four shale samples with different contents of total organic carbon. In addition, coupled with density distribution analyses, the work demonstrates that shale samples with lower total organic carbon contents typically signify a smaller radius of gyration with better oil mobility, which indicates a greater wave oscillation with a larger pore size to be estimated from the scattering vector. This work also elucidates the notable scenarios of an increasing pore size could correspond to a decreasing radius of gyration caused by mass density redistribution. For polydisperse systems, this research illustrates the variations in pore volumetric ratio impact the scattering intensity, whereas pore scale changes affect the oscillation pattern. This novel research of analyzing mass density distribution and pore scale information in real space is also suitable for other porous media systems.Document Type: Original articleCited as: Zhang, T., Hu, Q., Tian, Q., Ke, Y., Wang, Q. Small angle neutron scattering studies of shale oil occurrence status at nanopores. Advances in Geo-Energy Research, 2024, 11(3): 230-240. https://doi.org/10.46690/ager.2024.03.0
Challenges in mathematical modeling of dynamic mass transfer controlled by capillary and viscous forces in spontaneous fluid imbibition processes
Get PDFDynamic mass transfer due to spontaneous imbibition is of significant importance in various scientific and engineering applications, including environmental remediation, chemical reactors, microfluidic systems, and oil recovery processes. This article addresses the challenges in mathematical modeling of the dynamic mass transfer due to spontaneous imbibition controlled by capillary and viscous forces. A mathematical model was developed to seamlessly integrate the effects of capillary and viscous forces on mass transfer. The model was validated by comparison with numerical solution, which shows excellent consistency, indicating no error in the derivation of the analytical model. Case analysis suggested some limitations of the analytical model. The model does not work at the starting point of imbibition because of mathematical singularity. The current computing technology does not generate model results under all conditions due to the data-overflow issue associated with the exponential function involved in the analytical model. Although using numerical solution with finite difference method can eliminate the data-overflow problem, time step size must be small enough to achieve algorithm convergence and generate meaningful result.Document Type: Original articleCited as: Mahmood, M. N., Nguyen, V., Guo, B. Challenges in mathematical modeling of dynamic mass transfer controlled by capillary and viscous forces in spontaneous fluid imbibition processes. Capillarity, 2024, 11(2): 53-62. https://doi.org/10.46690/capi.2024.05.0
Influencing mechanisms of multi-scale pore-fracture responses of coals on their macro/micromechanical behaviors under ScCO2 injection
Get PDFTo decipher the mechanical response mechanisms of coal seams with multi-scale pore-fracture structure to supercritical CO2 (ScCO2) injection, two coal samples from different mines of the Ordos Basin, North China, were first selected for conducting ScCO2-water-coal reaction experiments. Subsequently, the pore-fracture structure, macroscopic and microscopic mechanical behaviors of samples with different reaction times were analyzed, and the evolution patterns of pore-fracture parameters and relationships between the macroscopic and microscopic mechanical parameters were finally elucidated. The results showed that the ScCO2-water-coal reaction modifies the pore-fracture structure in coal. Originally filled fractures re-open, original micro-fractures expand, new fractures form, and pores evolve from small- to large-sized. After the ScCO2-water-coal reaction, the evolution of the compaction stage, the macroscopic mechanical parameters and the energy dissipation during loading corroborate the weakening effect of the ScCO2-water-coal reaction on coal. The changes observed in the microscopic mechanical parameters align with those in the macroscopic mechanical parameters; however, due to the strong heterogeneity of coal and the inability of microscopic parameters to reflect the component and pore-fracture distribution, certain characteristics of the change amplitude of macroscopic and microscopic mechanical parameters of coal are inconsistent. The ScCO2 extraction effect, the chemical dissolution, the different-sized pore-fracture evolution, the coupling effect of geostress, reservoir pressure, and swelling stress are the main factors to consider during the process of ScCO2 sequestration in deep coal seams at the micro-, meso- and macro-scales, as they are responsible for potential safety issues.Document Type: Original articleCited as: Niu, Q., Wang, X., Chang, J., Wang, W., Liu, X., Wang, Q. Influencing mechanisms of multi-scale pore-fracture responses of coals on their macro/micromechanical behaviors under ScCO2 injection. Advances in Geo-Energy Research, 2024, 14(1): 64-80. https://doi.org/10.46690/ager.2024.10.08
Deformation characteristics and exploration potential of the West Kunlun foreland fold-and-thrust belt
Get PDFThe West Kunlun foreland is dominated by segmented fold-and-thrust belts with significant potential for hydrocarbon exploration, while the extent of exploration in this area has been relatively limited. In this paper, by conducting complex structural interpretation, the geometric and kinematic characteristics, as well as the variations in the segmented fold-and-thrust belts within this region are revealed. The West Kunlun foreland fold-and-thrust belts are divided into three structural segments, which exhibit distinct structural styles. The Pusha-Kedong segment in the east is characterized by large-scale northward propagation, with high-angle basement-involved faults in the root belt and thin-skinned thrusts in the front belt. Additionally, three-row anticlines developed in the middle to the upper structural layers. The Kashi-Yecheng segment, located in the middle, is characterized by strike-slip faults and basement-involved structural wedges transitioning to detachment structures. Within this segment, the Sugaite structure in the mountain front is a wedge structure composed of basement-involved faults and an upper back-thrust fault. Meanwhile, the Yingjisha structure in the thrust front consists of a fold in the lower part and a back-thrust system above it. The lower fold is controlled by the Cambrian detachment thrust, which terminates upward in the Paleogene, while the back-thrust faults truncate upper structural layers and terminate downwards in the Miocene strata. The Wupoer segment in the northwest is controlled by the Main Pamir Thrust and the Front Pamir Thrust, which are low angular forward thrust faults with an arc distribution. A piggyback basin has developed in the root belt and upper structural layer since the Pliocene. Based on the deformation characteristics and the accumulation of oil-gas reservoirs discovered so far, two types of oil and gas-rich thrust belts with different hydrocarbon exploration fields in the West Kunlun foreland are described.Document Type: Original articleCited as: Jiang, L., Dong, H., Li, Y., Zhao, W., Zhang, Y., Bo, D. Deformation characteristics and exploration potential of the West Kunlun foreland fold-and-thrust belt. Advances in Geo-Energy Research, 2024, 11(3): 181-193. https://doi.org/10.46690/ager.2024.03.0
Mechanisms of hydrocarbon generation from organic matters: Theories, experiments and simulations
Get PDFA comprehensive understanding of the characteristics and mechanisms underlying hydro carbon generation from organic matter has emerged as a pivotal challenge in deciphering the “life mystery” of oil and gas, thereby guiding strategic planning for the global petroleum industry. The swift advancements in materials science, drilling engineering, computer technology, big data, and artificial intelligence have furnished robust methodologies and tools for research into organic hydrocarbon generation. This perspective offers an analysis and synthesis of three distinct research paradigms pertinent to organic hydrocarbon generation: Theoretical analysis, experimental exploration, and numerical simulation. These three research modalities probe the mechanisms of organic hydrocarbon generation across varied scales, with their findings mutually reinforcing and validating each other. This synergy provides invaluable insights that contribute to a holistic understanding of organic hydrocarbon generation, facilitating a comprehensive assessment of the potential of subterranean oil and gas resources.Document Type: PerspectiveCited as: Du, S., Hu, T. Mechanisms of hydrocarbon generation from organic matters: Theories, experiments and simulations. Advances in Geo-Energy Research, 2024, 12(2): 156-160. https://doi.org/10.46690/ager.2024.05.0