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A deep-learning approach for reservoir evaluation for shale gas wells with complex fracture networks
Get PDFThe complex fracture networks in shale gas reservoirs bring greater challenges and uncertainties to the modeling in reservoir evaluation. As the emerging potential technology, deep learning can be usefully applied to many aspects of reservoir evaluation. To further conduct the reservoir evaluation in rate transient analysis, this work proposes a data-driven proxy model for accurately evaluating the horizontal wells with complex fracture networks in shales. The production time, variable bottom hole pressure, and the fracture networks properties are used as input variables, while the output variable refers to the production for the forecast time period. The data from boundary element method is used to generate the proxy model for the learning process. The method of shuffled cross-validation is used to increase the model’s accuracy and generalizability. The proxy model is coupled with recently developed deep learning methods such as attention mechanism, skip connection, and cross-validation to address the time series analysis problem for multivariate operating and physical parameters. Results demonstrate that the attention mechanism is robust. The operating parameters analysis shows that the attention mechanism has the ability to analyze variable pressure drop/flowrate data. Sensitivity analysis also indicates that the model takes into account the geometric characteristics of fracture network. The model reliability is proved by a case study from Marcellus shale. The computation time of the trained attention mechanism model is approximately 0.3 s, which equates to 3.8% of the physical model’s running time.Document Type: Original articleCited as: Chu, H., Dong, P., Lee, W. J. A deep-learning approach for reservoir evaluation for shale gas wells with complex fracture networks. Advances in Geo-Energy Research, 2023, 7(1): 49-65. https://doi.org/10.46690/ager.2023.01.0
Recent advances on shale oil and gas exploration and development technologies
Get PDFIn the face of the complex global energy transition, the development of unconventional oil and gas resources, such as oil shale, shale oil, and shale gas, encounters challenges related to carbon neutrality, technological complexities, and costs. However, the world’s strained energy landscape and the fact that the new energy industry has yet to take shape also present rich opportunities for the development of these resources. Against this background, a conference platform was established at Jilin University for facilitating scholarly exchange and discussion on the exploration and development technologies of shale oil and gas. The 5th International Symposium on Shale Oil and Gas Exploration and Development Technologies was successfully held in Changchun from November 10 to 12, 2023. The symposium attracted over 210 experts and scholars from more than 59 institutions worldwide, representing the field of shale oil and gas exploration, development, and utilization. Participating delegates shared their accomplishments in the realm of shale oil and gas exploration and development technologies, engaging in profound discussions and fruitful exchanges on these subjects.Document Type: EditorialCited as: Guo, W., Deng, S., Sun, Y. Recent advances on shale oil and gas exploration and development technologies. Advances in Geo-Energy Research, 2024, 11(2): 81-87. https://doi.org/10.46690/ager.2024.02.0
Opportunities and challenges in CO2 geologic utilization and storage
Get PDFCO2 geological utilization and storage is considered as an effective approach to deeply cut anthropogenic CO2 emissions. It is vital to enhance the amount of CO2 stored in the subsurface, at the same time to ensure safe and long-term subsurface storage of CO2 without any CO2 leakage. Science and engineering research in modeling concepts, experimental approaches, safety assurance and emerging CO2 geological utilization and storage technologies have driven the advancement of CO2 geological utilization and storage in recent years. In order to encourage communication and collaboration in CO2 geological utilization and storage research worldwide, a Sino-German joint symposium titled “Opportunities and Challenges in CO2 Geologic Utilization and Storage” was organized in Wuhan and Stuttgart from February 22 to 24, 2023, bringing together experts from China, Germany, and other countries. The symposium was jointly organized by Institute of Rock and Soil Mechanics, Chinese Academy of Sciences and Institute for Modelling Hydraulic and Environmental Systems, University of Stuttgart with financial support from the Sino-German Center for Research Promotion. A two-site hybrid meeting was held (participants in China met in Wuhan, participants in Germany met in Stuttgart, and other participants joined the meeting online), attracting more than 100 participants from around the world. The latest studies in the field of CO2 geological utilization and storage were presented at the symposium.Document Type: EditorialCited as: Zhang, L., Nowak, W., Oladyshkin, S., Wang, Y., Cai, J. Opportunities and challenges in CO2 geologic utilization and storage. Advances in Geo-Energy Research, 2023, 8(3): 141-145. https://doi.org/10.46690/ager.2023.06.0
Compressed air energy storage in salt caverns in China: Development and outlook
Get PDFWith the promotion of China’s carbon peaking and carbon neutrality goals, the energy industry is transforming from traditional fossil energy to renewable energy, which is sustainable, clean and safe. The development of renewable energy is not only an important measure to achieve the above goals but also a significant factor to alleviate the global energy crisis. Salt caverns, with good air tightness, have been considered as the best choice for large-scale underground energy storage. To elaborate on the research and future development of salt cavern compressed air energy storage technology in China, this paper analyzes the mode and characteristics of compressed air energy storage, explores the current development, key technologies and engineering experience of the construction of underground salt caverns for compressed air energy storage at home and abroad. Focusing on salt cavern compressed air energy storage technology, this paper provides a deep analysis of large-diameter drilling and completion, solution mining and morphology control, and evaluates the factors affecting cavern tightness and wellbore integrity. The future development and challenges of underground salt caverns for compressed air energy storage in China are discussed, and the prospects for the three key technologies of large-diameter drilling and completion and wellbore integrity, solution mining morphology control and detection, and tubing corrosion and control are considered. This paper aims to provide a useful reference for the development of underground salt cavern compressed air energy storage technology, the transformation of green and renewable energy, and the realization of carbon neutral vision.Document Type: Invited reviewCited as: Wan, M., Ji, W., Wan, J., He, Y., Li, J., Liu, W., Jurado, M. J. Compressed air energy storage in salt caverns in China: Development and outlook. Advances in Geo-Energy Research, 2023, 9(1): 54-67. https://doi.org/10.46690/ager.2023.07.0
Reservoir automatic history matching: Methods, challenges, and future directions
Get PDFReservoir history matching refers to the process of continuously adjusting the parameters of the reservoir model, so that its dynamic response will match the historical observation data, which is a prerequisite for making forecasts based on the reservoir model. With the development of optimization theory and machine learning algorithms, automatic history matching has made numerous breakthroughs for practical applications. In this perspective, the existing automatic history matching methods are summarized and divided into model-driven and surrogate-driven history matching methods according to whether the reservoir simulator needs to be run during the automatic history matching process. Then, the basic principles of these methods and their limitations in practical applications are outlined. Finally, the future trends of reservoir automatic history matching are discussed.Document Type: PerspectiveCited as: Liu, P., Zhang, K., Yao, J. Reservoir automatic history matching: Methods, challenges, and future directions. Advances in Geo-Energy Research, 2023, 7(2): 136-140. https://doi.org/10.46690/ager.2023.02.0
Molecular insights into structural and dynamic properties of water molecules in calcium silicate hydrate nanopores: The roles of pore size and temperature
Get PDFCalcium silicate hydrate is the primary hydration product of Portland cement and plays a crucial role in determining the strength of cement-based materials. The structural and dynamic properties of water molecules within calcium silicate hydrate nanopores have significant implications for the mechanical and durability performance of these materials. However, the influences of pore size and temperature on the properties of water molecules have not been fully explored. In this work, using molecular dynamics simulations and theoretical analysis, the evolution and mechanisms of the structural and dynamic properties of water molecules in different scenarios with various pore sizes and temperatures are systematically investigated. It is shown that the diffusion coefficients of water molecules increase with both pore size and temperature. Moreover, water molecules have a tendency to adsorb onto calcium silicate hydrate substrates, forming a distinct layered structure. As a result, the water molecules near the surfaces of calcium silicate hydrate substrates exhibit limited mobility, leading to smaller diffusion coefficients compared to those in other regions. Additionally, the distinctions in properties between water molecules and Ca2+ ions are elucidated and the underlying mechanisms behind these differences are also unveiled. The results and findings in this work deepen the understanding of structural and dynamic properties of water molecules within calcium silicate hydrate nanopores, providing valuable insights for improving the mechanical and durability performance of cement-based materials.Document Type: Original articleCited as: Liu, S., A, H., Tang, S., Kai, M., Yang, Z. Molecular insights into structural and dynamic properties of water molecules in Calcium silicate hydrate nanopores: The roles of pore size and temperature. Capillarity, 2023, 8(2): 23-33. https://doi.org/10.46690/capi.2023.08.0
Numerical study of response behaviors of natural gas hydrate reservoir around wellbore induced by water jet slotting
Get PDFThe trial production of natural gas hydrate reservoirs remains poor. Reasonable reservoir reconstruction, which can improve formation permeability, is an important approach to increasing the efficiency and enhancing production. In this work, water jet slotting is proposed to reconstruct an natural gas hydrate reservoir near a wellbore. The spatial slots formed by water jet slotting not only directly constitute high-permeability channels, but also generate disturbances to the surrounding in-situ sediment. Water jet slotting disturbances to nearby sediment was investigated using a three dimensional flow-structure coupling model to evaluate the proposed reconstruction method. The reservoir at the SH2 site in the Shenhu area of the South China Sea was used as the reference. A horizontal slotting arrangement along the vertical well was adopted. The results demonstrate that water jet slotting can change the primary stress state of the sediment around the wellbore, and generate a dominant stress relaxation zone and small stress concentration zone. Within the stress relaxation zone, the in-situ compressive stress was remarkably reduced or even transformed into tensile stress, accompanied by sediment displacement and volumetric expansion strain. This is conducive to loosening the sediment around the wellbore and improving the permeability characteristics. In addition, the influence of the water jet slotting parameters including slot radius, spacing, and number on disturbances to the nearby sediment was studied. Reservoir responses to water jet slotting under balanced and unbalanced bottom-hole pressures were compared and analyzed. This study provides a reference for natural gas hydrate reservoir reconstruction using water jet slotting.Document Type: Original articleCited as: Huang, M., Su, D., Zhao, Z., Wu, L., Fang B., Ning, F. Numerical study of response behaviors of natural gas hydrate reservoir around wellbore induced by water jet slotting. Advances in Geo-Energy Research, 2023, 7(2): 75-89. https://doi.org/10.46690/ager.2023.02.0
Impact of key parameters on far-field temporary plugging and diverting fracturing in fractured reservoirs: A 2D finite element study
Get PDFTemporary plugging and diverting fracturing technology is of utmost importance in stimulating fractured reservoirs. However, studies investigating the mechanisms of new fracture initiation and propagation during far-field temporary plugging and diverting fracturing have been scarce, and the optimal technique parameters are still unknown. To address this issue, a two-dimensional fracturing model is developed via the finite element method in this work, which simulates the temporary plugging effect using the equivalent viscosity temporary blockage method and the unrestrained growth of hydraulic fractures by globally embedding the cohesive element of zero-thickness. Then, some key parameters for far-field temporary plugging and diverting fracturing in fractured reservoirs are discussed and some interesting insights are given. Firstly, a lower-permeability plugging zone expedites the pressure increase within the fracture, thereby boosting the probability of achieving temporary plugging and diverting fracturing. The size of the plugging zone significantly impacts the pressure increase within the fracture. Secondly, the plugging position should be determined considering the density and arrangement of natural fractures in the layer, and the temporary plugging construction should be performed after maximizing the elongation of initial hydraulic fracture. Thirdly, an increase in fluid viscosity and injection displacement promotes the pressure rise inside the fracture. Nonetheless, the impact of injection displacement on temporary plugging and diverting fracturing surpasses that of fluid viscosity. Overall, the established model can inform the design of temporary plugging and diverting fracturing in fractured reservoirs.Document Type: Original articleCited as: Liu, P., Lou, F., Du, J., Chen, X., Liu, J., Wang, M. Impact of key parameters on far-field temporary plugging and diverting fracturing in fractured reservoirs: A 2D finite element study. Advances in Geo-Energy Research, 2023, 10(2): 104-116. https://doi.org/10.46690/ager.2023.11.0
Response law and indicator selection of seismic wave velocity for coal seam outburst risk
Get PDFThe accurate detection of coal seam stress field effectively prevents coal and gas outbursts. This study uses wave velocity, wave velocity anomaly coefficient, and wave velocity gradient as indicators to identify stress anomalies in coal seam. The results show that these three indicators of wave velocity are all positively correlated with load, while changes in the wave velocity anomaly coefficient and wave velocity gradient are more gentle than those of wave velocity. The degree of damage of coal can be judged by the wave velocity anomaly coefficient, while the transition between high and low stress zones can be identified by the wave velocity gradient. In areas affected by geological structures such as valleys and mountain tops, the coal seam wave velocity and wave velocity anomaly coefficient may exhibit anomalies. The comparative analysis of wave velocity and its derived indicators can reveal the stress state and coal structure of coal seam with higher accuracy, identify the areas affected by geological structures such as valleys and mountain tops, and determine the boundary of the stress relief zone after hydraulic fracturing. Combined with the actual geological structure characteristics of coal seam, it can accurately identify the stress disturbance region of coal seam and achieve the purpose of predicting coal and gas outbursts.Document Type: Original articleCited as: Qiu, L., Zhu, Y., Liu, Q., Guo, M., Song, D., Wang, A. Response law and indicator selection of seismic wave velocity for coal seam outburst risk. Advances in Geo-Energy Research, 2023, 9(3): 198-210. https://doi.org/10.46690/ager.2023.09.0
Multiphysics coupling in exploitation and utilization of geo-energy: State-of-the-art and future perspectives
Get PDFNatural gas hydrates and geothermal energy are potential sources of low-carbon geo-energy that are crucial in achieving a sustainable energy future for human society. The exploitation and utilization of these sources inherently involve thermal-hydraulic-mechanical-chemical coupling processes, and these complex coupling processes need to be numerically simulated for exploitation and utilization technology developments. This paper provides a brief overview of the current status and future challenges of numerical simulations for these coupling processes in the context of exploiting and utilizing natural gas hydrates, shallow and deep geothermal energy. It also presents perspectives on how to address these challenges, aiming to advance the development of numerical coupling technology within the geo-energy exploitation and utilization communities.Document Type: PerspectiveCited as: Wan, Y., Yuan, Y., Zhou, C., Liu, L. Multiphysics coupling in exploitation and utilization of geo-energy: State-of-the-art and future perspectives. Advances in Geo-Energy Research, 2023, 10(1): 7-13. https://doi.org/10.46690/ager.2023.10.0