Status quo and development trends of research on shale gas adsorption and seepage in shale gas reservoirs

Yi ZHANG^{¹^,²}(), Bin ZHANG^{¹^,²}, Banghua LIU^³, Jie LIU^⁴, Qiansheng WEI^⁴, Qi ZHANG^⁵, Hongjun LU^⁶, Pengyu ZHU^{¹^,²}, Rui WANG^{¹^,²^,⁷}

Shaanxi Key Laboratory of Well Stability & Rock Mechanics in Oil and Gas Reservoirs, Xi’an, Shaanxi 710065, China

School of Petroleum Engineering, Xi’an Shiyou University, Xi’an, Shaanxi 710065, China

Production & Operation Management Department, CNPC, Beijing 100083, China

No. 3 Gas Production Plant, Changqing Oilfield Company, PetroChina, Ordos, Inner Mongolia 017300, China

Gas Field Development Division, Changqing Oilfield Branch, PetroChina, Xi’an, Shaanxi 710018, China

Oil and Gas Technology Research Institute, Changqing Oilfield Branch, PetroChina, Xi’an, Shaanxi 710018, China

National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China

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Abstract

Shale gas reservoirs are characterized by large amounts of adsorbed gas within nano- to micron-scale organic pores and the mosaic form of organic matter in the inorganic matter. To understand these unique features, we initially review current methodologies used to characterize shale gas adsorption and seepage. Afterward, we summarize the mathematical representations of critical factors influencing these processes, including changes in the gas adsorption layer thickness, changes in the thickness of water film in inorganic pores, and changes in gas desorption-induced pores. Subsequently, we point out major problems in the current models of calculating the apparent permeability of shale gas reservoirs: (1) inaccurate characterization of reservoir pore structures; (2) a lack of methods to characterize the effects of the desorption of gas molecules dissolved into the solid organic matter on the adsorption of seepage flux; (3) inadequate characterization of the discrete distribution of organic matter in shale gas reservoirs; and (4) the unreasonability in direct application of parameters obtained from laboratory isothermal adsorption experiments, which neglects the differences between adsorbed shale gas and that dissolved into the solid organic matter in adsorption and desorption. Then, we analyze the advantages of the molecular simulation technique over physical experiments in examining shale gas adsorption and seepage. Accordingly, we summarize molecular simulation technique-based methods for modeling and simulating shale gas adsorption and seepage, as well as the simulation results. Finally, suggestions for further advancement in the molecular simulation of shale gas adsorption and seepage are put forward, including the improvement of multi-medium and multi-scale modeling methods based on conventional molecular models of inorganic and organic pores to be in line with the actual situation of shale gas reservoirs, as well as the necessity to develop methods for shale gas adsorption and seepage simulation that are more suitable for actual conditions.

Keywords

adsorption and desorption transport mechanism apparent permeability molecular simulation reservoir adsorption and seepage shale gas

CLC number: TE122.2 Document code: A Article ID: 0253-9985(2024)01-0256-25

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