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Multi-scale comprehensive study of the dynamic evolution of permeability during hydrate dissociation in clayey silt hydrate-bearing sediments
Get PDFThe exploitation of natural gas hydrates is in essence the process of hydrate dissociation from the solid phase into the gas and liquid phases, which is a complex problem involving phase transition and gas-water multi-phase flow. Permeability is a useful parameter for characterizing the flow capacity of sediments, and the pore-structure changes caused by hydrate dissociation make this parameter characterized by spatial and temporal evolution. Clayey silt sediments form the hydrate accumulation reservoir in the South China Sea, whose lithological characteristics (shallow buried deep, poor permeability, and low cementation) are unfavorable to fluid flow, leading to difficulties in the production prediction of clayey silt hydrate-bearing sediments. In this paper, the mutual feed-back mechanism between pore-structure and permeability during hydrate dissociation was clarified using the lattice Boltzmann model method. Core-scale seepage experiments were carried out to validate the dynamic evolution of permeability relationship. The permeability calculation module of Tough+Hydrate code was developed to quantitatively describe the evolution of this relationship, and the first hydrate production test in the Shenhu area was evaluated to validate the applicability of pore- and core-scale study at the site scale. This study clarifies the dynamic evolution mechanism of permeability during hydrate dissociation, and establishes a permeability evolution model in a S-shape suitable for clayey silt hydrate-bearing sediments.Document Type: Original articleCited as: Li, Y., Xu, T., Xin, X., Xia, Y., Zhu, H., Yuan, Y. Multi-scale comprehensive study of the dynamic evolution of permeability during hydrate dissociation in clayey silt hydrate-bearing sediments. Advances in Geo-Energy Research, 2024, 12(2): 127-140. https://doi.org/10.46690/ager.2024.05.0
Recent advancements and practices of fracturing technology in continental shale reservoirs
Get PDFIn continental shale reservoirs, the complex construction, limited fracture height and small stimulated volumes result in poor adaptability and low recovery efficiency when traditional shale fracturing techniques are used. This work introduces the recent improvements in fracturing technology developed for continental shale reservoirs and highlights the challenges and technological innovations required to enhance oil recovery. Lately, several innovative fracturing techniques have been developed that are suitable for the efficient development of continental shale reservoirs. These new proposed fracturing techniques primarily enhance the recovery of continental shale reservoirs by optimizing fracture creation and expansion, improving permeability, or increasing the stimulated reservoir volume. Several practical applications of these technologies in complex fault shale reservoirs, matrix-dominated shale reservoirs and complex structural shale reservoirs have demonstrated significant improvements in oil production. However, further research is needed with respect to determining the technical parameter boundaries for fracturing in different depressions and reducing costs, in order to refine these technologies and advance the efficient development of continental shale resources.Document Type: PerspectiveCited as: Zhang, F., Lu, M., Yang, F., Cao, G., Zhang, L. Recent advancements and practices of fracturing technology in continental shale reservoirs. Advances in Geo-Energy Research, 2024, 13(3): 237-240. https://doi.org/10.46690/ager.2024.09.0
Future potential research hotspots on the precise integration of geology and engineering in low-permeability oil reservoirs
Get PDFWhile petroleum scientists and engineers have increasingly acknowledged the significance of integrating geology with engineering for efficient petroleum development, the precise integration of above two aspects still requires substantial enhancement. This study identifies several potential future research hotspots in the precise integration of geology and engineering within low-permeability oil reservoirs. These include the accurate identification of sedimentary facies, which is constrained by horizontal wellbore logging, the three-dimensional continuous distribution modeling of heterogeneous start-up pressure gradients, and the determination of advantageous oil displacement paths driven by geomodels. The recommendation for future research is to employ advanced data analysis techniques to determine the correlation between experimental data at a small core scale indoors and multifunctional logging data. Additionally, fine geological modeling methods should be utilized to develop heterogeneous continuous distribution models of diverse reservoir geology and development attributes. This work offers several fresh perspectives for the efficient exploitation of Chinas continental low-permeability oil reservoirs in subsequent stages.Document Type: PerspectiveCited as: Du, S., Bai, L. Future potential research hotspots on the precise integration of geology and engineering in low-permeability oil reservoirs. Advances in Geo-Energy Research, 2024, 14(1): 4-7. https://doi.org/10.46690/ager.2024.10.0
Experimental study on production characteristics and enhanced oil recovery during imbibition and huff-n-puff injection in shale reservoir
Get PDFImbibition and huff-n-puff injection in shale reservoirs can significantly enhance oil recovery after depletion. To clarify the microscopic production characteristics and enhance the oil recovery mechanisms across different pore scales during imbibition and huff-n-puff injection, this study establishes an online physical simulation method that integrates imbibition and huff-n-puff using nuclear magnetic resonance and conducts a series of online nuclear magnetic resonance analyses under different imbibition systems. The microscopic production characteristics and dynamic development characteristics are quantitatively studied from the aspects of pore recovery and residual oil distribution. The results show that the occurrence states of pores of shale oil can be categorized into three types, including adsorption pore as the predominant type, followed by percolation pore and migration pore. When viewing the entire imbibition process comprehensively, it becomes imperative to maximize the recovery of migration pores while ensuring the recovery degree of adsorption pores. The recovery of free oil increases with the imbibition amount and the residual oil gradually shifts to adsorbed and organic matter-dominated forms, resulting in gradually decreasing recoverability. Using water-based imbibition media achieves a superior production effect for adsorbed oil in interlayered clay, whereas CO2 imbibition media can effectively improve the recovery of organic matter through mass transfer, leading to 11.01%-23.54% enhancement in oil recovery. Leveraging the bridge flow conductivity of fractures, fluid imbibition displacement and CO2 carrying effect emerges as a pivotal strategy for achieving optimal enhanced oil recovery.Document Type: Original articleCited as: Wei, J., Shang, D., Zhao, X., Zhou, X., Yang, Y., Du, M. Experimental study on production characteristics and enhanced oil recovery during imbibition and huff-n-puff injection in shale reservoir. Capillarity, 2024, 12(2): 41-56. https://doi.org/10.46690/capi.2024.08.0
Use of controlled fractures in enhanced geothermal systems
Get PDFEnhanced geothermal systems are typically tight and naturally fractured like unconventional oil and gas reservoirs, so the leading technology being evaluated for their commercial development is also multistage fractured horizontal wells. The state-of-the-art approach of thermal recovery from enhanced geothermal systems involves injecting cold water into a multiply fractured horizontal/deviated well and producing hot water from a parallel well above the injector. The limited control over the hydraulic fracture location, size, and orientation in multistage fractured horizontal wells results in low and unpredictable thermal recoveries. To this end, we present an alternative technology that employs unique configurations of mechanically cut fractures to recover heat efficiently from all parts of hot rocks in the subsurface. The precise control over these fractures’ location, size, orientation, and conductivity facilitates the design of suitable configurations of intersecting fractures. This paper presents high-resolution numerical studies of thermal recovery from both multistage fractured horizontal wells and the proposed approach. The results show that the proposed approach can recover significantly more thermal energy than multistage fractured horizontal wells. Additionally, the temperature profiles show that precise control over the location of the fractures allows the reliable and efficient recovery of heat from all parts of the enhanced geothermal systems, which could be the key to their commercial development.Document Type: Original articleCited as: Rashid, H. U., Olorode, O. Use of controlled fractures in enhanced geothermal systems. Advances in Geo-Energy Research, 2024, 12(1): 35-51. https://doi.org/10.46690/ager.2024.04.04
Revealing subsurface dynamics: Imaging techniques for optimizing underground energy storage
Get PDFSubsurface processes play a crucial role in determining the efficiency and viability of key applications with significant technical and economic implications, including hydrocarbon production, CO2/H2 geo-storage, and environmental engineering. A comprehensive understanding of natural behavior including microstructures, morphologies, and various petrophysical properties at pore scale is vital for optimizing the utilization of underground energy storage formations. Despite ongoing efforts, the behavior of diverse natural phenomena in the subsurface remains inadequately understood. This work leverages imaging techniques in conjunction with flow displacement experiments in investigating various natural phenomena, such as CO2/H2 geo-sequestration and fracture propagation. Additionally, the significance of microfluidic experiments in studying the dynamics of multiphase flows are briefly underscored. As a conclusion, porous media characterisation at pore scale is valuable for the advance in the understanding of natural phenomenon in subsurface engineering and the subsurface sciences, and upscaling them across space and time.Document Type: PerspectiveCited as: Zou, S., Zhang, Y., Ma, L. Revealing subsurface dynamics: Imaging techniques for optimizing underground energy storage. Advances in Geo-Energy Research, 2024, 12(1): 1-7. https://doi.org/10.46690/ager.2024.04.0
Accurate determination of nano-confined minimum miscible pressure to aid CO2 enhanced oil recovery and storage in unconventional reservoirs
Get PDFThe precise determination of minimum miscible pressure is of great importance for CO2 enhanced oil recovery and storage as it directly influences the efficiency of pore-scale oil displacement and CO2 trapping. In this study, an interpretable machine learning framework is developed, enabling the reliable evaluation of nano-confined minimum miscible pressure. Four machine learning algorithms (Random Forest, Multi-layer Perceptron, Support Vector Regression, and eXtreme Gradient Boosting) are employed to accurately predict the nano-confined minimum miscible pressure of a CO2-oil system. The results demonstrate that, excluding support vector regression, the determination coefficients for all models surpass 94%, signifying the robust predictive performance of our model. Subsequently, Shapley Additive exPlanations is used to analyze the feature importance ranking and the impact of each input feature on minimum miscible pressure in these models. Based on the interpretation results, our multi-layer perceptron model is superior in mining the input-output relationship and reflecting the petrophysical laws, rendering it highly suitable for predicting the minimum miscible pressure while considering nano-confinement. In addition, it is found that pore size significantly influences minimum miscible pressure prediction and that minimum miscible pressure decreases with decreasing pore size when the pore size is ≤75 nm. Single-factor sensitivity analysis is applied to validate the trend patterns between input features and minimum miscible pressure in the multi-layer perceptron model.Document Type: Original articleCited as: He, Y., Wei, B., Zhao, J. You, J., Kadet, V., Lu, J. Accurate determination of nano-confined minimum-miscible-pressure to aid CO2 enhanced oil recovery and storage in unconventional reservoirs. Advances in Geo-Energy Research, 2024, 12(2): 141-155. https://doi.org/10.46690/ager.2024.05.0
The effect of matrix-fracture permeability contrast on hydrocarbon foam performance in oil-wet carbonate
Get PDFFoam-based enhanced oil recovery methods are becoming instrumental in increasing hydrocarbon production from unconventional reservoirs. However, the efficacy of such techniques is significantly affected by reservoir heterogeneity and adverse wettability conditions. This experimental study addresses such challenges by investigating the effect of fracture-matrix permeability contrast on the effectiveness of foam-based enhanced oil recovery in fractured oil-wet porous systems under reservoir conditions. Fractured oil-wet Minnesota Northern Cream Buff carbonate core samples were employed and fracture permeability was varied using four different mixtures of proppants with varying mesh sizes. An amphoteric surfactant was used as the foaming agent and the aqueous solution was prepared in a synthetic brine of 200,000 ppm salinity. The results showed that foam reduced gas mobility in fractures, diverting gas to the matrix and mobilizing oil toward fractures. The permeability of the fracture showed a significant impact on foam behavior in oil-wet porous systems. It was noted that as the fracture-matrix permeability contrast decreased to a certain ratio, the apparent viscosity of the foam increased, resulting in the enhancement of fracture-matrix interactions and, therefore, higher oil recovery. However, further reduction in this ratio resulted in a significant decline in foam strength. The optimal fracture-matrix permeability contrast was determined when using 100 wt.% of 100 mesh sand, enabling the creation of small and durable bubbles, which notably restricted gas movement and led to higher oil recovery. The results confirm that foam can be a viable and effective alternative to traditional gas injection methods in fractured carbonates with oil-wet characteristics.Document Type: Original articleCited as: Youssif, M. I., Sharma, K. V., Goual, L., Piri, M. The effect of matrix-fracture permeability contrast on hydrocarbon foam performance in oil-wet carbonate. Advances in Geo-Energy Research, 2024, 13(3): 176-192. https://doi.org/10.46690/ager.2024.09.0
Characterization of pore systems in fine-grained carbonate rocks using digital core technology
Get PDFThe characterization of pore systems in fine-grained carbonate rocks faces numerous challenges due to the significant complexity of microscopic features, including a variation of micro- and nanoscale pore sizes and the complex pore-throat distribution. In this work, digital core technology was adopted to characterize the pore systems of lacustrine fine-grained carbonate rocks in the Yingxi area of Qaidam Basin. The simulated results indicated that the pore types predominantly contain intercrystalline and dissolution pores. The former exhibit high porosity but extremely low permeability and are primarily developed in bedded dolostones. Conversely, the latter show relatively higher permeability, predominantly developed in bedded calcareous dolostones. The elevated dolomite content provides the material basis for the development of intercrystalline pores, while the extremely small throat radius constrains the fluidity of this pore system. In addition, the dissolution has a great impact on improving the permeable capability of intercrystalline pore system via increasing the radius and specific surface area of pores and throats.Document Type: Research highlightCited as: Hu, C., Zhao, Z., Gao, S., Liu, C., Wu, K., Pang, P. Characterization of pore systems in fine-grained carbonate rocks using digital core technology. Advances in Geo-Energy Research, 2024, 12(1): 77-80. https://doi.org/10.46690/ager.2024.04.0
Microfluidic experiments and numerical simulation methods of pore-scale multiphase flow
Get PDFMultiphase flow is a common scenario in industrial and environmental applications. Especially at microscopic scale, accurately describing flow processes is challenging due to fluid-fluid, fluid-solid, and solid-solid interactions. Pore-scale microfluidics and numerical simulation methods considering complex topology are increasingly being applied to study multiphase flow phenomena. This work focuses the recent applications of microfluidic experiments and new numerical simulations in complex flows for enhanced oil recovery. Two types of coupling algorithms are provided to integrate the advantages of pore network model and direct numerical simulation methods. For fines migration, the computational fluid dynamics-discrete element method is proposed to describe the coupling process between fluid and solid particles. Pore-scale microfluidic experiments and simulation methods deals with complex flow processes at micro/nano scales, providing effective solutions for complex industrial processes.Document Type: PerspectiveCited as: Cai, J., Zhao, J., Zhong, J., Bate, B. Microfluidic experiments and numerical simulation methods of pore-scale multiphase flow. Capillarity, 2024, 12(1): 1-5. https://doi.org/10.46690/capi.2024.07.0