四川盆地川南地区侏罗系沙溪庙组沙一段沉积相特征与砂体展布

Depositional Facies Characteristics and Sand Body Distribution of Member 1 of the Shaximiao Formation, Jurassic, in the Southern Sichuan Basin

摘要: 为明确四川盆地川南地区沙溪庙组沙一段沉积相对致密气储层的控制作用，综合利用岩心、测井等资料，系统开展沉积相与砂体展布研究。结果表明：沙一段发育三角洲平原和三角洲前缘亚相，识别出分流河道、水下分流河道等七种微相；受双向物源控制，砂体呈树枝状–连片席状展布，垂向上经历三角洲前缘→平原→前缘的旋回演化。沙一¹亚段砂体连片性最佳，局部厚度超100 m，沙一²亚段因泥质分隔连通性变差，沙一³亚段非均质性增强。砂体高值带对应于分流河道及河口坝发育区，泥质沉积构成侧向遮挡。研究成果可为该区致密气勘探提供沉积地质依据。

Abstract: To clarify the controlling effects of sedimentary facies on relatively tight gas reservoirs in the Shaiximiao Formation, Member 1 in the southern Sichuan Basin, a systematic study on sedimentary facies and sand body distribution was conducted by comprehensively utilizing core and logging data. The results indicate that Member 1 of the Shaiximiao Formation developed delta plain and delta front subfacies, with seven microfacies identified, including distributary channels and subaqueous distributary channels. Controlled by bidirectional sediment sources, the sand bodies exhibit a dendritic to contiguous sheet-like distribution, undergoing a cyclical evolution vertically from delta front → plain → front. The sand body continuity is optimal in Submember 1 of Member 1, with local thickness exceeding 100 m, while connectivity deteriorates in Submember 2 of Member 1 due to muddy separation, and heterogeneity intensifies in Submember 3 of Member 1. High-value sand body zones correspond to areas with developed distributary channels and mouth bars, with mud deposits forming lateral barriers. These findings provide sedimentary geological evidence for tight gas exploration in the region.