四川盆地蓬溪-武胜台凹西侧长兴组成藏主控因素

Major controlling factors for hydrocarbon accumulation of Changxing Formation in west Pengxi-Wusheng intra-platform sag,Sichuan Basin

蓬溪-武胜台凹为开江-梁平海槽同期构造产物,其两侧的油气勘探一直未取得较大突破,成藏特征认识也不够清晰。文中在系统梳理烃源岩、储层、构造等成藏条件基础上,结合最新钻探成果,开展了成藏主控因素研究。结果表明,长兴组成藏具有3个基本条件,即多套优质烃源岩的发育,规模发育的礁滩储层,通源断层提供的油气垂向进入长兴组的通道。长兴组油气富集规律取决于2个要素:1)源储匹配。源储匹配不佳决定了长兴组未能大规模成藏,多套烃源岩中仅筇竹寺组在生、排烃期上与断层活动期的匹配较好,其余烃源岩对长兴组供烃有限;由于延伸至长兴组的断层较少,源储间有效通道缺乏又进一步导致了气源不足。2)生物礁滩储层发育状况。生物礁滩储层的连续发育促成了垂侧向复合输导体系的形成,在此基础上有限的烃类会逐步向斜坡高部位运移聚集,气水分布受构造影响较大,非“一礁一藏”。据此研究结果,优选了4个勘探有利区。

The Pengxi-Wusheng intra-platform sag is a contemporaneous tectonic product of the Kaijiang-Liangping trough.There have been no major breakthroughs in oil and gas exploration on either side of the Pengxi-Wusheng intra-platform sag,and the understanding of reservoir formation characteristics is not clear enough.Based on systematical analysis of hydrocarbon accumulation conditions such as source rocks,reservoirs and structures,and combining with the latest drilling results,major controlling factors for hydrocarbon accumulation were studied.The results show that there are three basic conditions for hydrocarbon accumulation in Changxing Formation,namely the development of multiple sets of high-quality hydrocarbon source rocks,a large-scale developed reef-shoal reservoir,and the channel for oil and gas to vertically enter Changxing Formation provided by the through-source fault.The hydrocarbon accumulation pattern of Changxing Formation is determined by two factors:(1)Matching of source and reservoir.Poor matching of source and reservoir determines that large-scale reservoirs have not occurred in Changxing Formation.Among multiple sets of hydrocarbon source rocks,only Qiongzhusi Formation has a good matching with the fault activity period in its hydrocarbon generation and expulsion periods,while other source rocks have limited hydrocarbon contributions to Changxing Formation.With only a few faults extending to Changxing Formation spatially,the lack of effective channels between source and reservoir further leads to insufficient gas sources.(2)Development status of biological reef-shoal reservoirs.The continuous development of biological reef-shoal reservoirs has led to the formation of a vertical-lateral composite transport system.On this basis,limited hydrocarbons will gradually migrate to the high parts of the slope.Gas-water distribution is greatly affected by structural characteristics,and situations like a reef forms a hydrocarbon reservoir are not common.Based on this study,four favorable exploration zones were selected.