摘要
川西坳陷是中国石化在四川盆地的重要探区之一,该区陆相致密砂岩气勘探近年来取得重要突破,发现了以上侏罗统致密砂岩为主力储层的成都大气田,但对其天然气来源及与邻区天然气特征差异的认识缺乏地球化学证据。天然气地球化学特征研究表明,成都大气田侏罗系致密砂岩气干燥系数(C_(1)/C_(1-5))介于0.939~0.982之间,δ^(13)C_(1)、δ^(13)C_(2)和δD_(1)值分别介于-33.7‰~-30.7‰之间、-25.4‰~-22.3‰之间和-162‰~-153‰之间,烷烃气碳、氢同位素系列均表现出正序特征。碳氢同位素组成揭示了侏罗系致密气为典型煤成气。根据煤成气二阶段分馏模式计算所得RO值与成都气田须家河组五段烃源岩实测RO值一致,反映了侏罗系致密砂岩气主体来自须五段烃源岩。研究区下侏罗统白田坝组基本不发育有效烃源岩,对侏罗系气藏没有显著贡献。受气源及成藏过程的差异影响,川西坳陷不同气田侏罗系天然气具有不同的地球化学特征。
The Western Sichuan Depression is one of the important exploration areas in the Sichuan Basin for SINOPEC,and natural gas exploration in terrigenous tight sandstone in the area has achieved great breakthrough in recent years.The Chengdu large gas field has been discovered in the main reservoirs of Upper Jurassic tight sandstone,however,few geochemical proofs have been provided to support the understanding of gas source and regional difference of natural gas.Studies on the geochemical characteristics indicate that,the Jurassic tight gas in the Chengdu large gas field has a dryness coefficient(C_(1)/C_(1-5))of 0.939~0.982,and theδ^(13)C_(1),δ^(13)C_(2),andδD_(1) values are in the ranges from-33.7‰to-30.7‰,-25.4‰to-22.3‰,and-162‰to-153‰,respectively,with positive carbon and hydrogen isotopic series of gaseous alkanes.The Jurassic tight gas is typically coal-derived gas as indicated by both carbon and hydrogen isotopic compositions.The calculated vitrinite reflectance(RO)values according to the two-stage fractionation model of coal-derived gas are consistent with the measured RO values of source rocks of 5th Member of Xujiahe Formation,which are demonstrated as the main source of the Jurassic tight gas.Effective source rocks are rarely developed in the Lower Jurassic Baitianba Formation of the study area,which is considered to have unsignificant contribution to the Jurassic gas reservoirs.The Jurassic natural gas from different gas fields in the Western Sichuan Depression displays different geochemical characteristics according to the effect of different gas source and accumulation processes.
作者
吴小奇
陈迎宾
王彦青
曾华盛
蒋小琼
胡烨
WU Xiaoqi;CHEN Yingbin;WANG Yanqing;ZENG Huasheng;JIANG Xiaoqiong;HU Ye(Research Center of Exploration and Development in Sichuan Basin,Research Institute of Petroleum Exploration and Production,SINOPEC,Chengdu 610041,China;Wuxi Research Institute of Petroleum Geology,Research Institute of Petroleum Exploration and Production,SINOPEC,Wuxi 214126,China)
出处
《天然气地球科学》
CAS
CSCD
北大核心
2021年第8期1107-1116,共10页
Natural Gas Geoscience
基金
国家自然科学基金项目(编号:41872122)
中国科学院战略性先导科技专项(A类)(编号:XDA14010402)联合资助。
关键词
川西坳陷
成都气田
致密砂岩气
地球化学特征
热成熟度
Western Sichuan Depression
Chengdu Gas Field
Tight sandstone gas
Geochemical characteristics
Thermal maturity
