## 2 Geological Setting  
The Sichuan Basin, one of the most significant oil and gas basins in the southwest of China, is situated in the northwestern part of the Yangtze Platform and extends towards the northwest. The basin is bordered by the Longmen Mountain Fold Belt to the northwest, the Daba Mountain Fold Belt to the northeast, the Qiyue Mountain Fold Belt to the southeast, and the E'mei Mountain Fold Belt to the southwest. According to the basement structure, the basin is composed of a northwest depression, central uplift, and southeast depression (Figure 1a) ([PERSON], 2016; [PERSON] et al., 2022; [PERSON] et al., 2022). Covering the Ediacaran to middle Mesozoic passive margin, the Sichuan Basin was a Late Mesozoic-Cenozoic foreland basin, which has featured a complex history of tectonics and sedimentation. Since the Chengliang tectonic movement (ca 700 Ma), the basin has subsequently experienced several significant tectonic episodes, including the Tongwan (ca 570 Ma), Caledonian (ca 439 Ma), Yunnan (ca 270 Ma), Dongwu (ca 256 Ma), Indosinian (ca 205-195 Ma), Yanshanian (ca 180-140 Ma), and Himalayan (ca 80-3 Ma) ([PERSON], 2016; [PERSON] et al., 2022).  
After the uplift of the Yangtze Plate in the Late Triassic, forming the foundation of the Sichuan Basin, the region entered a relatively stable stage of terrestrial basin sedimentation ([PERSON] et al., 2022; [PERSON] et al., 2022; [PERSON] et al., 2022). In the Early Jurassic, the Sichuan Basin was dominated by terrestrial sedimentary facies ranging from a shallow to deep lake, delta, alluvial fan, and alluvial plain ([PERSON], 2016; [PERSON] et al., 2022). Within the lake basin, from the center to the edge, three sub-facies developed in sequence: a deep to semi-deep lake, shallow lake, shell bank, delta, and fan delta (Figure 1a) ([PERSON], 2016; [PERSON] et al., 2022). Based on favorable temperature and depth conditions, the Jurassic of the Sichuan Basin is a primary source of shale oil resources ([PERSON], 2016; [PERSON] et al., 2022; [PERSON] et al., 2022).  
In the Early Jurassic, the basin formed extensive lacustrine clastic deposits, among which the largest, most extensive, and largest in area was the Zhenba Formation's Da'anzhai Member's lacustrine transgression, which has significant potential for hydrocarbon generation. The Jurassic Zhenba Formation from bottom to top can be divided into four members, Zhenzhu Chong, Dongyue Temple, Ma'anshan, and Da'anzhai, which are overlain by the Middle Jurassic Qianfoya Formation. The Da'anzhai Member is 70 to 125 m long and can be further divided into lower, middle, and upper sub-members based on lithological composition, electrical properties, and sedimentary cyclothem characteristics (Figure 1b). The lower sub-member of Da'anzhai represents a shallow lacustrine facies formed during the expansion of lake transgression, characterized by thick-bedded shell limestone. The middle sub-member of Da'anzhai is a semi-deep lake sub-facies with the longest period of lake transgression, developing thick-bedded shale. The upper sub-member of Da'anzhai represents a shallow lacustrine environment formed during lake regression, characterized by the interbedding of thick shell limestone layers with medium to thin mudstone layers [21, 35, 36].