川西地区上三叠统天然气成藏主控因素及勘探方向

Major controlling factors of gas pooling and exploration directions in the Upper Triassic in the western Sichuan Basin

四川盆地川西地区前陆盆地上三叠统沉积巨厚,发育了多套自生自储的天然气成藏系统。为了弄清该区天然气成藏的主控因素、寻找下一步油气勘探的方向,在分析天然气成藏条件的基础上,结合区域构造、油气演化的时空配置,探讨了油气运聚成藏机制及其主控因素。结果表明:川西上三叠统烃源岩层厚度大、有机碳含量高、生烃强度大,具有有利的天然气成藏条件;有效时空配置是成藏的关键,生烃强度控制气藏丰度,古今构造叠置决定气藏品质,大断裂控制气藏改造、重组和充满度。进而指出下一步的勘探方向:川西地区南部以勘探常压、构造圈闭型气藏为主,其中川西南部三和①号断层下盘的老君山和邛西①号断层下盘的桑园等构造应为构造圈闭气藏的首选目标;川西地区北部以勘探超压、岩性气藏为主,其中地层上倾方向的梓潼凹陷—九龙山构造之间的剑门—龙岗地区是岩性气藏勘探的重要领域。

The Upper Triassic sedimentary sequence is thick in the western Sichuan foreland basin and has multiple indigenous gas plays.On the basis of analyzing the main reservoir forming conditions and in combination with regional structures and hydrocarbon evolution as well as their configuration relationship between time and space,this paper discusses the mechanism and major controlling factors of hydrocarbon migration and accumulation.The Upper Triassic source rocks in the western Sichuan Basin are featured by great thickness,high TOC contents,and heavy hydrocarbon generation intensity,which are all favorable conditions for gas accumulation.The geometric configuration is the key to gas accumulation,hydrocarbon generation intensity controls the abundance of gas reservoirs,the superimposition of structures controls the quality of gas reservoirs,and large faults control the modification,recombination and fullness of gas reservoirs.This paper also presents the future exploration directions.It is highly possible that structural trap gas reservoirs with normal pressure occur in the southern part of the western Sichuan Basin,where the Laojunshan structures on the down-thrown walls of No.3 and No.1 faults and the Sangyuan structure on the Qiongxi-1 fault are the major targets of structural trap gas reservoirs.Lithologic gas reservoirs with normal pressure may occur in the northern part of the western Sichuan Basin,where the Jianmen-Longgang area between the Zitong sag and the Jiulongshan structure is the target of lithologic gas reservoirs.