Research on the Development Characteristics of Deep Shale Laminae —Taking the Longmaxi Formation in the Dazu Area of the Sichuan Basin as an Example

The deep shale gas resources are vast in scale and possess significant development potential. The study of lamination structure is crucial for evaluating the effectiveness of shale reservoirs. However, the understanding of the lamination development characteristics of deep shale in the Dazu area of the Sichuan Basin remains unclear, hindering further exploration and development. This study integrates core observation, thin section identification, and quantitative statistical methods to systematically investigate the lamination types, combination patterns, and spatial distribution laws of the Longmaxi Formation’s Longyi 1 sub-member shale in the study area. The results indicate that the laminations in the study area can be divided into two types: mud laminations (organic matter/clay) and silt laminations (siliceous/ calcareous). These can be further categorized into six lamination combination types: clay-siliceous (sparse) lamination group, calcareous-organic matter-rich (alternating) lamination group, calcareous-organic matter-rich (dense) lamination group, siliceous-organic matter-rich (sparse) lamination group, siliceous-organic matter-rich (alternating) lamination group, and siliceous-organic matter-rich (dense) lamination group. Vertically, the lamination density increases from bottom to top, with a transition from siliceous laminations to calcareous/clay laminations. Horizontally, the lamination density significantly decreases from the northwest to the southeast (from the Mituochang syncline to the Puluchang syncline), with a reduction in the proportion of calcareous laminations and a shift in lamination combination from dense to sparse.