塔北、塔中天然气中CO_2的碳同位素组成及成因探讨

CO2 是塔北、塔中天然气中常见的非烃组分。各油气区内的天然气中CO2 的δ13C值尽管有差别 ,但其表征的成因意义基本一致。塔中天然气中的CO2 可能存在两种来源 ,一种来源于烃源岩岩石和矿物及胶结物分解 ;第二种来自二叠纪火山活动过程中的脱气。轮台凸起构造单元上油气藏 (除雅克拉外 )中CO2来自库车坳陷T -J陆相烃源岩中有机质转化。东河塘天然气中CO2 来自寒武 -奥陶海相碳酸盐岩岩石分解及泥岩中碳酸盐矿物分解

CARBON ISOTOPIC COMPOSITION AND ORIGIN OF CARBON DIOXIDE IN NATURAL GASES IN NORTHERN AND CENTRAL TARIM BASIN

Carbon dioxide is one of the non-hydrocarbons which occur in natural gases in northern and central Tarim Basin. The δ13C values of carbon dioxide are different from one oil (gas) field to another, but all the δ13C values of carbon dioxide from the same oil (gases) field imply that CO2 is relatively homogeneous in origin. The five δ13C values of carbon dioxide in central Tarim Basin are within the carbon isotopic range of abiogenic carbon dioxide ,and the carbon dioxide probably has two sources : one originated from the decomposition of hydrocarbon-source rocks or carbonate minerals and carbonate cements in the hydrocarbon-source rocks, and the other from degassing during Permian volcanism in central Tarim Basin. Carbon dioxide in natural gases from oil (gas) deposits (except Xa-Ke-La oil (gas) field) in the Luntai salient originated from the Permian-Jurassic continental facies hydrocarbon-source rocks. The contents of CO2 in natural gases from the Denhetang oil (gas) field are very high ,and the δ13C values are within the carbon isotopic range of abiogenic carbon dioxide ,and carbon dioxide was derived from decomposition of the Cambrian-Ordovician marine facies carbonate rocks and carbonate minerals in mudstones.