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Integrated rock physics characterization of unconventional shale reservoir: A multidisciplinary perspective
Get PDFRenowned for its organic richness, unconventional shale presents both unique challenges and opportunities for hydrocarbon extraction and various geo-engineering applications, owing to its complex storage, flow, and stimulation properties. It is essential, from a multidisciplinary perspective, to characterize the rock physics response and construct rock physics model for unconventional shale reservoirs. A maturity-constrained rock physics modeling method for shales, in conjunction with geochemical analyses, is proposed, employing the stepwise homogenization method to quantify the scale-dependent elastic and anisotropic behavior of laminated shales. Considering the complex pore structure of shale, combined with the microscale effects of fluid transport, various forces, and microfracture features, the multiphase fluid flow behavior can be accurately characterized. Then, from the perspective of fracturing performance, it is necessary to develop a new fracability evaluation model for unconventional shale reservoirs. This model integrates fracture mechanics theory, the elastic and mechanical properties of rocks, fracturing operations, reservoir geological characteristics, and in-situ stress to thoroughly evaluate fracability. Unconventional petrophysicists must move beyond traditional hydrocarbon evaluation to embrace interdisciplinary approaches, which requires comprehensive understanding and characterization of the storage, flow, and stimulation capacities, thereby optimizing development strategies and maximize resource utilization.Document Type: PerspectiveCited as: Zhao, L., Zhao, Y., Yan, D., Zhu, J., Cai, J. Integrated rock physics characterization of unconventional shale reservoir: A multidisciplinary perspective. Advances in Geo-Energy Research, 2024, 14(2): 86-89. https://doi.org/10.46690/ager.2024.11.0
From traditional extrapolation to neural networks: Time-depth relationship innovations in the subsurface characterization of Drava Basin, Pannonian Super Basin
Get PDFThe estimation of time-to-depth relationships can prove challenging in regions with rare acoustic logs. This study focuses on the eastern part of the Drava Basin in north Croatia, chosen as a mature hydrocarbon exploration area with abundant geophysical and well data. As only a small portion of wells have well log measurements or seismic profiling performed, a time-to-depth extrapolation is often performed, which potentially results in the erroneous placement of well log markers in the time domain and affects the interpretation of seismic sections or volumes. This study proposes a novel methodology for predicting two-way travel time values in wells without vertical seismic profiling or acoustic logging. This research evaluates the parameters for the characterization of the velocity distribution in the subsurface and the efficiency of artificial neural networks versus conventional methods for this task. The constructed artificial neural network model has a correlation coefficient above 0.99 for the training, testing, and validation datasets, with a mean absolute error of approximately 25 milliseconds for each network. Artificial neural networks proved to have a lesser error in predicting the two-way time and are not sensitive to outlier values.Document Type: Original articleCited as: Kamenski, A., Cvetković, M., Kapuralić, J., Kolenković Močilac, I., Brcković, A. From traditional extrapolation to neural networks: Time-depth relationship innovations in the subsurface characterization of Drava Basin, Pannonian Super Basin. Advances in Geo-Energy Research, 2024, 14(1): 25-33. https://doi.org/10.46690/ager.2024.10.0
Tensile behavior and damage mechanisms of hot dry rock under thermal shock fatigue and seawater dissolution
Get PDFSignificant potential exists for mining hot dry rock in coastal areas, oceans, islands, and reefs by utilizing abundant seawater as a heat-exchanging medium. It is crucial for optimizing reservoir stimulation technology to explore mechanical characteristics and mechanisms for damage of reservoir rocks during seawater mining of hot dry rock. In this research,granite was subjected to several heat treatment temperatures (100 to 500 °C) and various numbers of fatigue thermal shocks (0-20) using seawater before Brazilian splitting tests and acoustic emission testing. The findings show that temperature, the thermal shocks, and seawater dissolution are the main factors influencing granite’s tensile strength.The temperature threshold for significant degradation of tensile strength, resulting from thermal shock from seawater and heat treatment, ranges from 200 to 300 °C. At high temperatures (300 to 500 °C), seawater decreases the tensile strength of granite by approximately 1.67 times compared to freshwater in cycles 0-10, and by about 3.20 times in cycles 10-20. In general, the higher the temperature and frequency of seawater impact, the greater the plasticity of the rock, the lower the tensile strength, and the higher the cumulative count and energy of acoustic emission. The number of seawater thermal shocks and granite’s tensile strength have a negative link that is substantially amplified by the temperature. The double effects of seawater cold cycle and heat treatment temperature cause granite to become more porous and progressively shift from tensile to shear damage. These results provide a benchmark for utilizing seawater as a thermogenic medium in enhanced geothermal systems for mineral extraction procedures.Document Type: Original articleCited as: Li, C., Tu, J., Xie, H., Hu, J. Tensile behavior and damage mechanisms of hot dry rock under thermal shock fatigue and seawater dissolution. Advances in Geo-Energy Research, 2024, 13(2): 132-145. https://doi.org/10.46690/ager.2024.08.0
A new near-wellbore modeling method for deviated wells in corner-point grid
Get PDFThis paper presents the construction of a high-quality, robust hybrid grid for near-wellbore modeling in the vicinity of a deviated well. The far-field region is modeled using a corner-point grid, while the near-wellbore region-referred to as the volume of interest-is remeshed using a layered unstructured grid, which consists of a combination of Voronoi and radial sub-grids. A detailed gridding and simulation workflow is outlined. The construction of the novel layered unstructured grid begins with building a base surface grid on the surface typically aligned to middle well point. The grids on the other surfaces are built through preserving the base topology but adjusting the nodes of base grid to fit the well points deviating from the base well point. A flow-based node rearrangement method is proposed to adjust the grid nodes to gain high-quality grids on each surface. The positions of new nodes are determined by ensuring equal streamlines and pressure values between nodes on the base and target surfaces, improving grid orthogonality as streamlines remain perpendicular to equipotential lines. The method’s ability to generate high-quality grids for deviated wells is demonstrated through illustrative and validation examples. Computational performance is assessed through direct comparisons across three case studies, showing that the new near-wellbore modeling model provides accurate well solutions and pressure maps with a reasonable computational cost. Additionally, the near-wellbore modeling model outperforms standard models in capturing gas flow with high compressibility, describing flow behavior in heterogeneous reservoirs, and predicting production parameters in multilayer systems.Document Type: Original articleCited as: Li, J., Zhao, L., Møyner, O., Lie, K. -A. A new near-wellbore modeling method for deviated wells in corner-point grid. Advances in Geo-Energy Research, 2025, 15(2): 112-128. https://doi.org/10.46690/ager.2025.02.0
Advances in the microscopic and mesoscopic simulation technologies developed for subsurface gas storage
Get PDFSubsurface gas storage refers to the practice of storing natural gas or other gases in underground reservoirs. It plays a crucial role in ensuring a stable and reliable supply of energy, especially during periods of high demand or supply disruptions. This work collectively highlights the significance of the microscopic and mesoscopic reservoir simulation techniques developed for subsurface gas storage. Specific technology progresses are demonstrated for a better storage of hydrogen and carbon dioxide, which meets well with the current focus on carbon reduction. In particular, molecular dynamics simulations can provide insight for the microscopic mechanisms affecting the adsorption and leakage of stored gas. Pore-network model generated using the advanced algorithm can determine the geological scenario for further flow and transport simulations.Document Type: PerspectiveCited as: Zhang, T., Liu, J., Yang, X., Sun, S. Advances in the microscopic and mesoscopic simulation technologies developed for subsurface gas storage. Advances in Geo-Energy Research, 2024, 14(1): 1-3. https://doi.org/10.46690/ager.2024.10.0
Mechanical characterization of uniaxial compression associated with lamination angles in shale
Get PDFThis paper investigates the mechanical properties and damage laws of marine shale from the Silurian Longmaxi Formation by conducting uniaxial compression experiments with varying lamination angles with respect to the loading direction. Data are analyzed via computed tomography scanning and fractal theory to reveal a series of mechanical properties, considering stress-strain curve, compressive strength, Young’s modulus, and Poisson’s ratio. The results indicate three damage modes in shale samples: shear, tension shear, and tension. The shales are anisotropic as the mechanical properties vary with the lamination orientation and the loading direction. The compressive strength decreases nonlinearly with increasing lamination angle, whereas the Young’s modulus and Poisson’s ratio correlate almost linearly with the lamination angle. To overcome the defect of visual images when quantitatively evaluating cracks and rock damage to investigate the mechanical properties of shale, we propose block fractal dimension and crack fractal dimensions calculated using post-experimental photographs and computed tomography images. Fractal dimensions are useful tools for identifying variations in uniaxial compressive strength and correlate positively with the sample damage, particularly their damage class. This study highlights the value of applying fractal theory for the quantitative characterization of shale mechanical properties, and reveals that the lamination orientation to the loading direction is a parameter that significantly controls the mechanical properties of shale.Document Type: Original articleCited as: Gao, M., Yang, M., Lu, Y., Levin, V. A., He, P., Zhu, H. Mechanical characterization of uniaxial compression associated with lamination angles in shale. Advances in Geo-Energy Research, 2024, 13(1): 56-68. https://doi.org/10.46690/ager.2024.07.0
Numerical simulation of ultrasonic wave propagation characteristics in water-based drilling fluid
Get PDFUltrasonic wave propagates with strong penetration, high stability, and has non-contact nature, therefore it is widely used in the petroleum industry. As an application example, an ultrasonic flowmeter can accurately measure the annular flow rate of water-based drilling fluid. According to the outlet flow rate, it can be noticed if there is an abnormal situation in the well to avoid accidents such as well kick and blowout. However, due to the attenuation of ultrasonic wave in the drilling fluid, the relevant research results are not reliable. Herein, based on the theory of acoustics, the influences of water-based drilling fluid density, solid particle size and solid particle number on the ultrasonic attenuation characteristics under different frequencies are studied by numerical simulation. First, the propagation characteristics of ultrasonic wave in water-based drilling fluid are systematically analyzed, then the accuracy of the above results is verified by laboratory tests. The results show that the ultrasonic attenuation rate is positively correlated with the solid particle size, solid particle number and ultrasonic frequency in water-based drilling fluid, while it is negatively correlated with the density of water-based drilling fluid. Furthermore, it is established that the ultrasonic energy decreases with increasing propagation distance. The results of this study can provide a theoretical basis and practical guidance for using an ultrasonic flowmeter to accurately measure the annulus return flow rate of drilling fluid and develop an intelligent drilling system, so as to improve the efficiency of field operation and drilling success rate.Document Type: Original articleCited as: Wan, J., Zhao, Y., Zhou, Y., Li, J., Dong, S., Sun, P. Numerical simulation of ultrasonic wave propagation characteristics in water-based drilling fluid. Advances in Geo-Energy Research, 2024, 13(1): 69-80. https://doi.org/10.46690/ager.2024.07.0
Microfluidic insights into CO2 sequestration and enhanced oil recovery in laminated shale reservoirs: Post-fracturing interface dynamics and micro-scale mechanisms
Get PDFSubsequent CO2 injection can enhance oil recovery and achieve carbon sequestration in shale reservoirs, which is crucial for energy sustainability and environmental protection. However, for continental sedimentary shale oil, the development process must consider the multiscale matrix-fracture structure and the impact of heterogeneous wettability on f luid-solid interactions. Moreover, the mechanisms of CO2 miscibility and interfacial behavior in post-fracturing reservoirs remain unclear. In this study, a laminated shale micro-model with fracture based on scanning electron microscopy observations was designed, and the process of fracturing fluid flowback and subsequent CO2 huff-n-puff were simulated. Results showed that forced imbibition primarily affects limestone layers, while spontaneous imbibition affects mudstone layers, contributing 89.3% and 10.7% to the affected area, respectively. The oil recovery mechanism of CO2 is mainly influenced by pressure, transfer from displacement-carry at low pressure to dissolution-extraction, and eventually to diffusion-extraction in the miscible state. Additionally, before reaching miscibility, Taylor dispersion, Kelvin-Helmholtz instability, Rayleigh-Taylor instability, and Marangoni effects occur at the oil-CO2 interface, leading to interfacial turbulent instability. Lastly, water huff-n-puff produces membrane and isolated droplet residual oil, while immiscible CO2 breaks cluster residual oil into columnar residual oil. Miscible CO2 enhances the recovery of various residual oils, improving oil recovery and facilitating CO2 storage. This study provides insights for post-fracturing CO2 huff-n-puff development of continental sedimentary shale oil and CO2 sequestration, promoting energy utilization and environmental improvement.Document Type: Original articleCited as: Li, L., Zhang, D., Su, Y., Zhang, X., Lu, M., Wang, H. Microfluidic insights into CO2 sequestration and enhanced oil recovery in laminated shale reservoirs: Post-fracturing interface dynamics and micro-scale mechanisms. Advances in Geo-Energy Research, 2024, 13(3): 203-217. https://doi.org/10.46690/ager.2024.09.0
Determining CO2 storage efficiency within a saline aquifer using reduced complexity models
Get PDFCarbon capture and storage is vital for reducing greenhouse gas emissions and mitigating climate change. Most projects involve the permanent geological storage of CO2 within deep sedimentary rock formations, but accurately constraining storage capacity usually involves detailed and computationally demanding reservoir modeling and simulation. Efficiency factors can also be used but these often lead to capacity overestimations. To address this, a workflow is proposed harnessing various existing, reduced complexity models that account for the surface topography and dynamic fluid behavior in a computationally efficient manner. This workflow was tested in an area of the Malay Basin mapped from three-dimensional seismic data but with illustrative reservoir parameters. A static analysis was first undertaken using algorithms within MRST-co2lab. Structural traps, spill paths and spill regions were identified using the reservoir topography. This provided initial indications into optimal well placement and led to refinement of the total capacity of the area into the capacity available within structural traps. This was followed with a dynamic analysis, also within MRST-co2lab, using computationally efficient Vertical Equilibrium models. Hundreds of simulations were undertaken and the optimal well placement was determined based on the maximum storage efficiency achieved. The results indicated that the amount that can be contained within this area is 15 times less than equivalent predictions using static storage efficiency factors. The advantage of such a light approach is that sensitivity and uncertainty analysis can be carried out at speed, before targeting certain parameters/areas for more detailed study.Document Type: Original articleCite as: de Jonge-Anderson, I., Ramachandran, H., Nicholson, U., Geiger, S., Widyanita, A., Doster, F. Determining CO2 storage efficiency within a saline aquifer using reduced complexity models. Advances in Geo-Energy Research, 2024, 13(1): 22-31. https://doi.org/10.46690/ager.2024.07.0
Rock permeability evolution during cyclic loading and colloid migration after saturation and drying
Get PDFThe study of the influence of cyclic loading on the permeability of rocks has been conducted for a long time. Despite the extensive research database, the actual reasons for the decrease in permeability during loading have not been fully revealed. One of these reasons, as described in the research, is the migration of colloids. This paper presents the findings of a study on colloid migration as one of the causes of permeability degradation in porous rocks under cyclic loading. Permeability is measured by injecting nitrogen at a constant pressure. The cyclic loading program is designed to eliminate the effects of residual deformations, creep, and gas slippage. Direct and reverse nitrogen blowings with increased injection pressure were performed between loading cycles. These blowings promote colloidal movement within the porous medium, leading to the blocking of pore throats and changes in permeability. A notable aspect of this work is that cyclic testing was performed both before and after the saturation and drying procedure. Stuck colloids that could not be moved by blowing are mobilized during saturation and drying. Comparative tests of cores after saturation and drying confirm the effect of colloid migration on permeability and enable the examination of whether plastic deformations caused permeability degradation in previous loading cycles. Additionally, it was observed that when saturated, new colloids can detach due to the Rehbinder effect, significantly reducing permeability.Document Type: Original articleCited as: Kozhevnikov, E., Turbakov, M., Riabokon, E., Gladkikh, E., Guzev, M., Panteleeva, A., Ivanov, Z. Rock permeability evolution during cyclic loading and colloid migration after saturation and drying. Advances in Geo-Energy Research, 2024, 11(3): 208-219. https://doi.org/10.46690/ager.2024.03.0