四川盆地晚二叠世—早三叠世沉积演化及其对天然气富集的意义

四川盆地上二叠统—下三叠统碳酸盐岩地层中富集天然气,天然气藏的分布受优质烃源岩和礁滩相储层的控制。为了揭示四川盆地沉积演化背景下天然气的富集规律及预测成藏有利区,对晚二叠世—早三叠世扬子古板块地质构造背景进行分析,讨论地质构造背景控制下四川盆地晚二叠世—早三叠世沉积演化特征;根据不同时期构造和沉积演化特征确定优质烃源岩和储层的发育机理和分布范围;结合天然气成藏模式的认识,确定天然气成藏有利区。结果表明:四川盆地晚二叠世—早三叠世海湾及其后陆棚的发育演化控制了该区龙潭组主力烃源岩与长兴组—飞仙关组礁滩相储层的发育分布,形成了下生上储的有利配置关系;川东北地区长兴组—飞仙关组台地边缘礁滩相储层邻近龙潭组海湾相优质烃源岩的区域为天然气成藏最有利区。总之,四川盆地晚二叠世—早三叠世沉积演化特征控制了海相优质烃源岩和储层的发育分布,决定了天然气的富集与分布。

Late Permian-Early Triassic Sedimentary Evolution in Sichuan Basin and Its Significance on Gas Accumulation

Upper Permian-Low Triassic carbonate formations in Sichuan Basin enrich gas, and the distribution of gas accumulation is controlled by high quality source rocks and reef-shoal facies reservoir. In order to reveal the gas enrichment rule and forecast the favorable areas under the sedimentary evolution settings in Sichuan Basin, the geological structure settings of Late Permian-Early Triassic Yangtze palaeoslab were analyzed, and the characteristics of Late Permian-Early Triassic sedimentary evolution under the geological structure settings were discussed; the development mechanism and distribution of high quality source rocks and reservoirs were explained according to the characteristics of tectonic evolution in different periods; combined with the gas accumulation model, the favorable areas of gas accumulation were divided. The results show that the development evolution of Late Permian-Early Triassic bay and shelf in Sichuan Basin controls the development and distribution of major source rocks in Longtan Formation and reef-shoal facies reservoirs in Changxing Formation-Feixianguan Formation, and the lower-generating and upper-reservoiring are favorable source-reservoir matching combination; the platform margin reef-shoal facies reservoir in Changxing Formation-Feixianguan Formation of Northeast Sichuan nearby the high quality source rocks of bay facies in Longtan Formation is the most favorable area for gas accumulation. In general, the characteristics of Late Permian-Early Triassic sedimentary evolution in Sichuan Basin control the development and distribution of marine facies high quality source rocks and reservoirs, and then determine the enrichment and distribution of gas.