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

Abstract

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 Triassic 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 1280 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 stimulation, 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 gas field, and the large source connecting strike-slip fault zones are the main breakthrough directions of natural gas exploration in fault-controlled carbonate rocks.