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四川盆地东部天然气中CO2含量多数小于2%,但H2S含量大于5%时CO2含量普遍较高.川东地区天然气13C1值较高,与H2S含量之间没有明显关系.油型气样品普遍发生了甲、乙烷碳同位素倒转,而煤成气样品则表现出正序特征.天然气中CO2的δ13C1值大致可以分为较低(24‰～12‰)和较高(8‰～4‰)两类.这些天然气具有较低的R/Ra值和分布较广的CO2/3He比值,与幔源气体不同,CO2均为典型壳源成因.高δ13CCO2值的天然气均位于川东北地区,其中低(不)含H2S气藏中的CO2主要来自二叠纪岩浆活动和高热流作用下碳酸盐岩的热分解,而TSR反应程度较高的气藏中的CO2则主要来自碳酸盐岩储层在酸性较强的地层水中发生的去白云岩化作用,TSR成因的CO2基本进入到次生方解石中.川东的中、南部地区天然气则具有低的δ13CCO2值,该区受峨眉山地幔柱活动影响较小,天然气中的CO2均为有机成因,其中卧龙河气田天然气尽管经历了TSR作用,但反应程度相对较低,地层水酸性较弱,储层尚未发生去白云岩化,CO2仍以TSR成因的为主,具有较低的δ13C值.
The content of CO2 in natural gas in the eastern Sichuan Basin is mostly less than 2%, but the content of CO2 is generally high when the content of H2S is more than 5%. There is no obvious relationship between the content of H2S and the 13C1 in natural gas in eastern Sichuan. The δ13C1 values of CO2 in natural gas can be roughly divided into lower (24 ‰ ~ 12 ‰) and higher (8 ‰ ~ 4 ‰) two These natural gas have lower R / Ra value and wider distribution of CO2 / 3He ratio, and are different from mantle gas.Carbon dioxide is a typical crustaceous origin.The natural gas with high δ13CCO2 value is located in northeastern Sichuan with low No) CO2 in H2S-bearing gas reservoirs mainly comes from the thermal decomposition of carbonate rocks under Permian magmatism and high heat flux, whereas CO2 in gas reservoirs with high TSR reactivity mainly comes from carbonate reservoirs The dolomitization of TSR causes the secondary conversion of TSR into secondary calcite, while the natural gas in central and southern Sichuan has a low δ13CCO2 value, which is affected by the Emeishan plume activity Smaller, natural gas CO2 are organic causes, including Wolong River Despite the TSR effect, natural gas in the gas field has a relatively low degree of reaction, low acidity in the formation water and no dolomitization in the reservoir. The CO2 is still dominated by TSR and has a relatively low δ13C value.