Intelligent identification and distribution of faults and associated fracture zones in tight sandstone reservoirs: A case study of the fifth member of Triassic Xujiahe Formation in Wubaochang area, northeastern Sichuan Basin, SW China

The faults and associated fracture zones in the tight sandstone reservoirs of the fifth member of the Triassic Xujiahe Formation (Xu-5 Member) in the Wubaochang area, northeastern Sichuan Basin, play a critical role in controlling gas well productivity. To delineate the distribution patterns of the faults and associated fracture zones in this area, a transfer-trained convolutional neural network (CNN) model and an XGBoost (eXtreme Gradient Boosting)-based intelligent seismic attribute fusion method were employed to identify faults and fracture zones, respectively, enabling precise characterization of their spatial distribution. The faults in the Wubaochang area are classified into first- to fourth-order structures, with the average fracture zone width on the hanging wall exceeding that of the footwall, demonstrating a strong positive correlation between fracture zone width and fault displacement. The study area is divided into three distinct deformation regions (southern, central and northern regions) featuring five fault structural styles (duplex, duplex-backthrust, imbricate thrust, synclinorium imbricate-backthrust, and anticlinorium imbricate-backthrust) and four corresponding fracture zone development patterns (duplex, duplex-backthrust, synclinorium imbricate-backthrust, and anticlinorium imbricate- backthrust). Based on the controlling effects of faults on gas enrichment, the dual-source hydrocarbon-supply zones are interpreted to be distributed in the northern and central regions, while the southern region is identified as gas-escape zones. By integrating the distribution of favorable reservoir development areas and fracture zones, two classes of gas enrichment zones (Class I and II) are delineated. Class I zones are primarily distributed in the northern region and the transitional zone from the southern to central regions, whereas Class II zones are concentrated in the central region. Class I zones exhibit dual-source hydrocarbon-supply conditions, larger-scale fracture zone development, and higher favorability compared to Class II zones. According to the defined gas accumulation effectiveness in different types of fracture zones, a high-productivity gas well model for the Wubaochang area is proposed, emphasizing “dual-source faults controlling enrichment, effective fracture zones controlling high production, and high matrix porosity ensuring sustained production”. Targeted drilling directions for different favorable zones are further optimized based on this model.