Tectonic evolution of the Leshan-Longnüsi paleo-uplift and its control on gas accumulation in the Sinian strata

摘要

Based on structural interpretation of the recent seismic data in central Sichuan Basin, combined with data of drilling and outcrops around the basin, this paper discusses the evolutional characteristics of unconformities at various stages in the Leshan-Longnüsi paleo-uplift, and studies the evolution of the paleo-uplift and its control on Sinian gas reservoir accumulation. Sinian, Paleozoic, Mesozoic and other major regional unconformities were developed in the Leshan-Longnüsi paleo-uplift. According to characteristics and denudation thickness of the unconformities, the paleo-uplift tectonic evolution is divided into four stages, namely, embryonic, developmental, stable burial, and finalization. The analysis of the effects of the tectonic evolution on the Sinian gas accumulation show that: (1) the unconformities controlled the development of ancient karst reservoirs relevant to paleo-weathering crust; (2) the tectonic evolution of the paleo-uplift controlled evolution of organic matter and hydrocarbon migration and accumulation; (3) morphological changes of the paleo-uplift controlled the formation and the mergence of structural traps.