Significant progress has been made in exploring shale gas resources in the middle-upper Permian strata of western Hubei.However,the unclear geochemical characteristics and origins of the gas have hindered a comprehens...Significant progress has been made in exploring shale gas resources in the middle-upper Permian strata of western Hubei.However,the unclear geochemical characteristics and origins of the gas have hindered a comprehensive understanding of reservoir evolution and have constrained integrated resource development.This study involved a 28-h desorption experiment in which gases released from shales of the Dalong and Gufeng Formations were systematically collected for compositional and carbon—hydrogen isotope analyses.Comparing the compositional and geochemical characteristics of the desorbed gases and investigating their genetic origins resulted in four main findings:(1)Gas composition during the middle stage of desorption,excluding H_(2)S,best represents the original reservoir fluid,with component variations linked to adsorption and diffusion capacities.(2)Both shales display similar gas compositions with trace H_(2)S;the Dalong shale contains lower CH_(4),CO_(2),and H_(2)S but higher C_(2)H_(6)and N_(2).(3)Carbon and hydrogen isotopes indicate oil-type thermogenic gases,with carbon isotope reversal reflecting tectonic uplift,depressurization,and the mixing of primary kerogen-derived and secondary oil-/condensate-derived gases.(4)N_(2)likely originates from ammonium-bearing silicate decomposition,CO_(2)is mainly inorganic,from thermal carbonate decomposition with minor organic contribution,and H_(2)S may result from oil cracking or thermochemical sulfate reduction.This study provides a comprehensive record of the fluid characteristics of middle-upper Permian shale gas reservoirs and enhances the understanding of their formation and evolution.展开更多
基金supported by the Hubei Provincial Natural Science Foundation of China(Grant No.2022CFB490,2024AFD381)Science and Technology Project of Hubei Geological Bureau(Grant No.KJ2024-2,KJ2025-14)Open Fund of Technology Innovation Center for Shale oil and Gas Accumulation Theory and Engineering in Southern Complex Structural Area,China Geological Survey(Grant No.SOG-202410).
文摘Significant progress has been made in exploring shale gas resources in the middle-upper Permian strata of western Hubei.However,the unclear geochemical characteristics and origins of the gas have hindered a comprehensive understanding of reservoir evolution and have constrained integrated resource development.This study involved a 28-h desorption experiment in which gases released from shales of the Dalong and Gufeng Formations were systematically collected for compositional and carbon—hydrogen isotope analyses.Comparing the compositional and geochemical characteristics of the desorbed gases and investigating their genetic origins resulted in four main findings:(1)Gas composition during the middle stage of desorption,excluding H_(2)S,best represents the original reservoir fluid,with component variations linked to adsorption and diffusion capacities.(2)Both shales display similar gas compositions with trace H_(2)S;the Dalong shale contains lower CH_(4),CO_(2),and H_(2)S but higher C_(2)H_(6)and N_(2).(3)Carbon and hydrogen isotopes indicate oil-type thermogenic gases,with carbon isotope reversal reflecting tectonic uplift,depressurization,and the mixing of primary kerogen-derived and secondary oil-/condensate-derived gases.(4)N_(2)likely originates from ammonium-bearing silicate decomposition,CO_(2)is mainly inorganic,from thermal carbonate decomposition with minor organic contribution,and H_(2)S may result from oil cracking or thermochemical sulfate reduction.This study provides a comprehensive record of the fluid characteristics of middle-upper Permian shale gas reservoirs and enhances the understanding of their formation and evolution.
