川中乐山—龙女寺古隆起震旦系天然气成藏条件分析

Formation of the gas reservoirs of the Leshan-Longnvsi Sinian palaeo-uplift in central Sichuan

认为四川盆地中部乐山—龙女寺古隆起震旦系含油气系统属多源多期成藏的复合含油气系统 ,烃源主要来自下寒武统筇竹寺组底部腐泥型暗色泥岩 ,其次为震旦系灯影组三段暗色藻白云岩和页岩 ;最有利的储盖组合是以灯影组四段、三段为储集层和以下寒武统黑色页岩为盖层的组合 ,其次是灯影组三段中部的白云岩段储盖组合。灯三段烃源岩在奥陶纪末—志留纪进入大量生烃期 ,生成的液态烃在古隆起顶部形成古油藏 ,志留纪末的抬升终止了第一期成烃作用 ,晚二叠世以来进入二次生烃期 ;三叠纪—中侏罗世 ,筇竹寺组烃源岩进入主要生烃期 ,在古隆起顶部灯影组风化壳形成古油气藏 ;晚侏罗世—早白垩世 ,筇竹寺组烃源岩处于生气高峰期 ,古油气藏的液态烃热裂解成气态烃 ,这些气态烃聚集形成现今的气藏。乐山—龙女寺古隆起震旦系储盖和保存条件较好 ,高石梯—磨溪潜伏构造带及华蓥山构造带是有利勘探区。图 4表 2参

The palaeo uplift of Leshan Longnvsi in central Sichuan Basin, in age of Sinian, is a complex petroleum system formed with many sources and periods,in which the hydrocarbon source is generated from sapropelic material dark shale in Qiongzhusi Formation basis, Lower Cambrian, then the dark seaweed dolomite and shale in the third member of Dengying Formation (Sinian). The Dengying Formation member Ⅲ hydrocarbon source reached peak generation period between Ordovician and Silurian, generated liquid hydrocarbons formed palaeo reservoir in top of the palaeo uplift. The first hydrocarbon generation was stopped around the end of Silurian. The second generation began in the Later Permian. From Triassic to Middle Jurassic, hydrocarbon source in Qiongzhusi Formation reached the main generation period, and the palaeo reservoir formed on Dengying Formation weathering crust on the top of palaeo uplift. From Later Jurassic to Early Cretaceous,the Qiongzhusi Formation reached a high generation,liquid hydrocarbons after thermal cracking became gaseous hydrocarbon in palaeo reservoir,which gaseous hydrocarbon formed present reservoir after accumulation. Leshang Longnvsi palaeo uplift Sinian reservoir cap rock is perfectly conservative, the Gaoshiti Moxi structural belt and Huayinshang structural belt should be the potential target.