Cratonic strike-slip fault systems in the central Sichuan Basin, China

Abstract

Accurate definition of strike-slip fault systems is critically important for understanding the evolution of petroleum systems and the distribution of hydrocarbons in many basins. Our study characterizes the structure of cratonic strike-slip faults in the Sichuan Basin, China, and the role that they play in hydrocarbon systems. Using two- and three-dimensional seismic reflection surveys, well data and field mapping, we describe strike-slip faulting in the central Sichuan basin related to gypsum-salt layers in the Lower-Middle Triassic section. We identify six main strike-slip fault zones in the central Sichuan Basin based on the two different structural configurations between strike-slip faulting and its associated deformation, and the offset positions of carbonate platform margins in the Upper Ediacaran Dengying Formation. Moreover, through quantitative analysis of a representative growth structure between two strike-slip fault zones, combined with the analysis of regional structures, paleography, and diagenetic events, we define five stages in the evolution of strike-slip fault system. During these stages, characterized by transtentional deformation, the fault system controlled the paleogeography within the cratonic basin and defined vertical and lateral migration paths for diagenetic and hydrocarbon fluids. As such, strike-slip faults are a key factor controlling the formation and evolution of the multi-layer petroleum system in the central Sichuan Basin. The shallow continental tight oil and gas deposits accumulate in the structure traps within the Triassic-Jurassic section associated with the strike-slip faulting. The deeper, marine cracked gas migrated and accumulated along the strike-slip faults, forming a pattern of multi-layer accumulations with different hydrocarbon compositions. Our results show that strike-slip faults are important structural element that has influenced the sedimentary evolution and distribution of hydrocarbons in the central Sichuan Basin. This well documented case study provides insights into the structures and petroleum geology of other ancient cratonic basins with strike-slip faulting worldwide.