Discovery of Intra-Cratonic Rift in the Upper Yangtze and Its Control Effect on the Formation of Anyue Giant Gas Field

Abstract

According to the drilling and seismic data, the Late Sinian-Early Cambrian intra-cratonic rift was found in Deyang-Anyue area of the Upper Yangtze craton. This rift is controlled by tensional fault and distributed in NNW trending with the NS length of 320km and EW width of 50-300km. After three stages of rift evolution, i.e., the forming stage, developing stage and dying stage, a favorable near-source accumulation assemblage was formed. The research results indicate that: (1) the sedimentary stage of Late Sinian Dengying Formation is the rift forming stage, during which through-basin facies sedimentation is developed in the rift, while platform marginal facies mounds and shoals are developed on both side, controlling the formation and distribution of high-quality reservoirs in Dengying Formation; (2) the sedimentation stage of Early Cambrian Meishucun-Qiongzhusi Formation is the rift developing stage, during which deep-water continental shelf facies argillaceous rocks are filled in the rift with a thickness of 500-1,000m, indicating the sedimentation stage of high-quality source rocks; (3) the sedimentation stage of Canglangpu Formation is the rift dying stage, terminating the evolution history of intra-cratonic rift by gap filling. The intra-cratonic rift is a key factor for the formation of Anyue giant gas field, where the high-quality source rocks provide abundant gases for the giant gas field. A regional lateral sealing occurred during the rapid rising of the western paleo-uplift in Central Sichuan during the Late Yanshan-Himalayan period, favorable to the preservation of the Gaoshiti-Moxi giant gas field on the east wing of the rift. The intra-cratonic rift and its role in giant gas accumulation provide a significant reference for deep oil and gas exploration in paleo-craton basins.