Control of tectonic movement on hydrocarbon accumulation in the Sinian strata, Sichuan Basin

All the tectonic movements occurring in the evolutionary history of the Sichuan Basin play a significant controlling role in the formation and transformation of hydrocarbon reservoirs in this basin, which is discussed herein in this paper. Based on seismic, logging and core data in combination with field outcrop investigation, an investigation was made into the tectonic movements in this study area and its control on the reservoir formation and trap transformation. In conclusion, four tectonic movements including the Tongwan Movement controlled the process of hydrocarbon accumulation in the Sinian strata in the Sichuan Basin. The Tongwan Movement was dominated by regional uplifting and subsidence. Its I and II episodes led to the formation and wide distribution of the near-surface palaeokarst reservoirs in the 2nd and 4th members of Dengying Fm. The Caledonian Movement resulted in the formation of Leshan-Longnüsi Paleohigh, forming the structural setting of the hydrocarbon enrichment belts in the Sinian strata. During the Hercynian-Indosinian period, the Sinian experienced tectonic movement dominated by overall subsidence, the early paleohighs were inherited, and the Sinian-Cambrian source rocks went into peak oil generation stage, leading to the development of large paleo-oil pools on the paleohighs. During the Indosinian Movement at the late Middle Triassic, the Sichuan Basin went into an evolution stage of a foreland basin, and the Sinian strata were deeply buried, leading to the pyrolysis of oil in the paleo-oil pools into gas which acted as the source of gas in the Sinian strata. The late Yanshanian-Himalayan period was the critical stage for the adjustment of gas reservoirs in the Sinian strata. It is believed that the Sinian in the Sichuan Basin has favorable conditions for gas accumulation, thus having large exploration potential. The Sinian reservoir in the Leshan-Longnüsi paleohigh is a favorable gas play and the slope zone of the paleohigh is another potential exploration target area.