库车坳陷东部吐格尔明地区天然气地球化学特征及油气充注史

库车坳陷东部油气地质条件复杂,天然气成因与油气充注时间存在争议,油气充注史不明,制约其油气勘探进程。利用天然气组分、碳同位素组成、流体包裹体岩相学与均一温度等分析测试数据,结合沉积埋藏史及构造演化史,研究了库车坳陷东部吐格尔明地区天然气地球化学特征、天然气成因类型及油气充注时间,分析了油气充注成藏过程。结果表明:吐格尔明地区天然气组分以甲烷为主,甲烷含量为75.56%~90.11%,干燥系数为0.79~0.93;δ¹³C₁和δ¹³C₂值为-35.73‰~-33.80‰和-26.41‰~-25.30‰,天然气成因类型属于成熟阶段的煤成气。吐格尔明地区侏罗系砂岩储层发育两类流体包裹体,分别为黄色液态烃包裹体和蓝白色荧光的气液烃包裹体、灰色的气烃包裹体,表明该区存在两期油气充注,第一期为13~7 Ma的原油充注,第二期为2.6 Ma以来的天然气充注。康村组早中期,吐格尔明地区烃源岩形成的原油充注至宽缓背斜圈闭中保存;库车组晚期,侏罗系克孜勒努尔组与阳霞组发育良好的源储组合,天然气近距离充注成藏。

Geochemical Characteristics of Natural Gas and Hydrocarbon Charging History of the Tugeerming Area in the Eastern Kuqa Depression

The oil and gas geological conditions in eastern Kuqa Depression are complex. The origin of natural gas, the time and history of oil and gas charging are disputed, which hampers regional oil and gas exploration. Based on the analyses on carbon isotope composition of natural gas, fluid inclusion petrography and homogenization temperature, and integrating the sedimentary/ burial history and tectonic evolution, the geochemical characteristics of natural gas and hydrocarbon accumulation process at Tugeerming area (eastern Kuqa depression) are revealed. The results show that methane is the main natural gas component at Tugeerming, with its content ranging from 75.56% to 90.11% and the dryness coefficient from 0.79 to 0.93. The δ¹³C₁ (-35.73% to -33.80‰) and δ¹³C₂ (-26.41‰ to -25.30‰) values suggest that the genetic type of natural gas is mature coal-derived gas. There are two types of inclusions in the Jurassic sandstone reservoirs at Tugeerming, i.e., yellow liquid hydrocarbon inclusions and bluish-white fluorescent gas-liquid hydrocarbon inclusions and gray gas-liquid hydrocarbon inclusions. This indicates two oil and gas charging stages at Tugeerming: (1) 13 Ma to 7 Ma crude oil charging, and (2) 2.6 Ma natural gas charging. In the Lower and Middle Kangcun Formation, the crude oil formed by source rocks at Tugeerming was charged into the wide and gentle anticlinal trap for preservation. In the Upper Kuqa Formation, the Jurassic Kezilenuer and Yangxia Formations developed good source-reservoir assemblage, with natural gas being charged at close distance to form the reservoirs in the Upper Kuqa Formation.