Identification of strike-slip fault zones and their petroleum geological significance in the tight sandstone reservoirs of the Xujiahe Formation, Wubaochang Area, northeastern Sichuan Basin

The enrichment patterns of natural gas in the tight sandstone reservoirs of the Xujiahe Formation in the northeastern Sichuan Basin are complex, and the fault system exerts a crucial control on hydrocarbon accumulation. To clarify the structural characteristics of the faults and their impact on natural gas enrichment in this area. Based on three-dimensional seismic data and drilling data, integrated with artificial intelligence fault identification technology and structural analysis, this study identifies a NE-SW trending en echelon strike-slip fault zone in the Xujiahe Formation of the Wubaochang Area, northeastern Sichuan Basin. The structural deformation characteristics, evolutionary history, and reservoir-controlling and accumulation-controlling effects of this fault zone are investigated. The results indicate that the fault zone exhibits vertically layered deformation characteristics: it manifests as thrust faults in the strata from the Upper Ordovician to the Lower Triassic Jialingjiang Formation, while in the Upper Triassic Xujiahe Formation, it appears as a strike-slip fault zone composed of a series of small NNW-SSE trending thrust faults arranged in a right-stepping en echelon pattern. The fault zone underwent two stages of tectonic evolution. During the Indosinian-Yanshanian period, under continuous SE-NW oriented tectonic compression, it exhibited thrust fault activity. In the Himalayan period, the regional tectonic stress field shifted, and under a NE-SW oriented horizontal compressional stress field, the pre-existing major faults underwent sinistral strike-slip movement, forming a series of right-stepping en echelon strike-slip faults in the Xujiahe Formation. The faults in the Xujiahe Formation are interconnected with the deep-seated major faults, linking the Xujiahe Formation reservoir, the Longtan Formation source rocks, and deep fluids. This connection establishes a “strong below and weak above” transport system and a “dual-source hydrocarbon supply” model. Simultaneously, it exerts a dual effect on the tight sandstone reservoirs of the Xujiahe Formation, namely “dissolution and porosity enhancement” and “cementation and destruction,” providing favorable dynamic conditions for the differential evolution of tight reservoirs and the development of sweet spot reservoirs. Consequently, the fault zone serves as a favorable site for natural gas enrichment and preservation in the tight sandstone reservoirs of the Xujiahe Formation. The research demonstrate that strike-slip fault zones are advantageous enrichment belts for natural gas in Triassic tight sandstone reservoirs in the northeastern Sichuan Basin, and greater emphasis should be placed on the evaluation and exploration of such target areas.