Distribution and gas exploration of the strike-slip faults in the central Sichuan Basin

The Sichuan Basin has abundant oil and gas resources and it has been generally acknowledged as a super petroliferous basin. In recent years, immense exploration and development potential of deep natural gas emerges in the Sichuan Basin. The identification of strike-slip faults and their reservoir controlling effects are of great significance to develop a new exploration domain of fault-controlled gas reservoirs. In order to clarify the distribution of strike-slip faults in the Sichuan Basin and their relationships with natural gas exploration, in view that the strike-slip faults in this basin are small and complex with poor seismic data and influenced more by the fold deformation of Tertiary gypsum salt beds, this paper identifies strike-slip faults and analyzes their characteristics, distribution and genesis based on the interpretation of continuous 3D seismic data of the central Sichuan Basin. Then, the fault-controlled gas reservoir model of strike-slip fault is established by reviewing old wells and evaluating geological conditions of hydrocarbon accumulation. Finally, the exploration potential and exploration direction of fault-controlled gas reservoirs are discussed. And the following research results are obtained. First, intraplate weak strike-slip faults can be identified by combining the seismic profile marker of strike-slip fault with the plane marker. Second, eight large strike-slip fault zones with a total length of 1 280 km are identified and confirmed in the central Sichuan Basin. Third, strike-slip faults are mainly distributed in the Sinian-Permian System, mainly composed of small-displacement oblique faults and echelon faults, and different in stratification, grading, classification and segmentation. Fourth, under the control of the oblique subduction of the Proto-Tethys Ocean and the different structures of the basement, the strike-slip faults in the central Sichuan Basin were formed in the Sinian and there are multiple stages of inherited Caledonian-Hercynian activities. Fifth, the strike-slip faults in the central Sichuan Basin play a role in source-reservoir connection, reservoir reconstruction, and gas accumulation and high yield, and constitute the fault-controlled natural gas accumulation system of three-element controlling reservoir and composite hydrocarbon accumulation based on source rock, fault and reservoir. In conclusion, a large intraplate strike-slip fault system is developed in the Sichuan Basin, which has the geological conditions of hydrocarbon accumulation to form strike-slip fault-controlled large gasfield, and the large source connecting strike-slip fault zones are the main breakthrough directions of natural gas exploration in fault-controlled carbonate rocks. © 2021, Natural Gas Industry Journal Agency. All right reserved.