Distribution and origin of the columnar sag anomalies of Maokou formation in southwestern Sichuan basin

Based on high-precision 3D seismic data, coherent slices, and forward modeling, and referring to the existing understanding of the“Faulted Solution” of the Ordovician in the Tarim basin, the newly discovered reservoir type of the middle Permian Maokou formation in southwestern Sichuan-columnar sag volume distribution characteristics and causes are analyzed. The results show such anomalous bodies are widely developed near the strike-slip faults of the northeastward basement in southwestern Sichuan. The seismic profile shows continuous downward sag of multiple sets of isotropic axes, extending from the top of the Maokou formation to the Sinian basement. Coherent slices are circular or ring-like features. Based on the analysis of the existing geological data, it is considered that such anomalous bodies are mainly caused by hydrothermal dissolution. The northeast strike-slip fault activated during the Emei rift during the Xingkai rift is the main controlling factor for its distribution. The study is of certain significance for expanding the exploration areas and zones in Southwest Sichuan and increasing reserves and production.