Paleo-geomorphology formed during Tongwan tectonization in Sichuan Basin and its significance for hydrocarbon accumulation

Abstract

Through analyzing the nature and periods of Tongwan tectonization, by using seismic data, drilling data and outcrop data, the pre-Qiongzhusi Formation eroded paleo-geomorphology was described with remaining thickness and moldic methods, and the hydrocarbon accumulation conditions were analyzed. The Sichuan Basin and its adjacent areas experienced Tongwan tectonization from late Sinian to early Cambrian which include three episodes that all manifested as regional uplift and erosion, forming three disconformities. Affected by that movement, a large scale Deyang-Luzhou eroded valley in N-S direction was formed in Central-Southern Sichuan Basin. In the valley, thick Maidiping Formation and Qiongzhusi Formation are Cambrian important source kitchens; they form good source-reservoir combinations with two sets of weathering karst reservoirs in Deng 2 and Deng 4 Member in Dengying Formation, favorable for the formation of large gas field with huge resource potential. The analysis of forming mechanism and evolution history of the eroded valley shows the thrusting-fold uplifting and erosion in the second episode of Tongwan tectonization in late Sinian period, and the extensional movement in the background of rapid marine transgression in early Cambrian are key to the formation of the eroded valley.