Sequence-Lithofacies Paleogeography of the Jialingjiang Formation in the Ziyang-Shizhu Area, Sichuan Basin, and Its Petroleum Geological Significance

[Objective]This study focuses on the Lower Triassic Jialingjiang Formation in the Ziyang-Shizhu area, central Sichuan Basin. This formation is an important gas-producing interval in the study area, where gas fields such as Moxi and Wolonghe have been discovered. However, due to the lack of a unified internal sequence stratigraphic framework and unclear understanding of sedimentary facies distribution and evolution, the distribution patterns of grain banks and the key controlling factors of high-quality reservoirs remain ambiguous, which restricts the prediction of favorable zones and exploration deployment in the region.[Method]Integrating core, well log, drilling, physical property analysis, and seismic data, combined with INPEFA analysis, a systematic sequence stratigraphic study of the Jialingjiang Formation was carried out. The paleogeomorphology of the Jialingjiang Formation was reconstructed, the lithofacies paleogeography of the study area was clarified, and the controlling factors of grain banks and favorable reservoirs were determined.[Result]The results show that the Jialingjiang Formation can be divided into two third-order sequences (SQ1, SQ2) and five fourth-order sequences (SSQ1–SSQ5). Three main subfacies are developed: open platform, restricted platform, and evaporative platform. Grain banks are mainly developed in the open platform and restricted platform subfacies. The development and distribution of grain banks are coupled with paleogeomorphological configuration and sea-level changes. The uplift–depression pattern, characterized by the Moxi submarine high, the Shizhu paleo-uplift, and the Linshui-Fengdu intra-platform depression, dominates the location and distribution pattern of grain banks, exhibiting a significant “uplift-depression controlled bank” feature. High-quality reservoirs are controlled by favorable sedimentary environments and moderate dolomitization.[Conclusion]This study clarifies the sequence lithofacies paleogeography of the Jialingjiang Formation, identifies the favorable development areas of grain banks, and establishes the relationship between reservoirs and sedimentary subfacies, providing a reliable geological basis for oil and gas exploration in the study area.