Geochemical Characteristics of Natural Gas in the Upper Permian Reservoir of the Eastern Sichuan Basin， China: Implication of Multiple Sources Mixing
作者机构：Natural Gas Geology Key Laboratory of Sichuan Province Southwest Petroleum University School of Geoscience and Technology Southwest Petroleum University Chongqing Gas District PetroChina Southwest Oil and Gas Field Company
出 版 物：《Journal of Earth Science》 (地球科学学刊)
年 卷 期：2023年
核心收录：
学科分类：081803[工学-地质工程] 08[工学] 0818[工学-地质资源与地质工程]
基 金：supported by the National Natural Science Foundation of China (Grant No. 42072184 41702157) the Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance
摘 要：For an improved understanding of gas enrichment mechanism in the eastern Sichuan Basin， South China， twelve natural gas samples were obtained from carbonate reservoirs of the Upper Permian strata to analyze the hydrocarbon and non-hydrocarbon gas compositions， stable carbon and hydrogen isotopes ratios of hydrocarbons， and noble gas isotope ratios. The gas samples in the Upper Permian reservoirs principally consist of alkane gas with a dryness ratio ranging from 127.9 to 1564.4. The carbon isotope ratio of methane (δ13C1) was almost constant at –34.1‰ to –31.3‰， but the carbon isotope ratio of ethane (δ13C2) varied from –36.6‰ to –25.8‰. The hydrogen isotope ratio of methane (δ2HC1) also displayed a wide range from –137‰ to –127‰. The large variations in the dryness ratio， δ13C2，and δ2HC1with almost constant δ13C1suggest the mixing of sapropelic and humic origins for hydrocarbon gases in these reservoirs. A high concentration of hydrogen sulfide (H2S) originated from the thermochemical sulfate reduction (TSR)， which was positively correlated with δ13C1(or δ13C2) in individual gas fields. TSR altered δ13C1(or δ13C2) and resulted in the abnormal character of isotopic reversal in the individual samples. The δ13C1(or δ13C2) in most gas samples， independent of H2S concentration， further displayed reversed carbon isotopes because of the mixture of thermogenic gases with various thermal maturity levels. The measured argon isotope ratio (40Ar/36Ar) varied from 310 to 1225， which suggests that the oldest 320 Myr source rock age corresponds to Permian shales. The analysis of the gas origin and the identification of primary source rock have made a significant contribution to further understanding the resource potential and distribution of natural gas in the Upper Permian， and have great implications for gas exploration in the eastern Sichuan Basin.
同方期刊数据库