Fault structure characteristics and fracture development patterns in Xujiahe Formation of Tongjiang-Maolubei area, northwestern Sichuan Basin

Multiple phases of fault structures are developed in the fault-fracture gas reservoirs of the Xujiahe Formation in the Tongjiang-Malubei area, northeastern Sichuan Basin. The reservoirs primarily consist of fault-associated fractures, fold-associated fractures, and matrix pores generated by fault activity, which are superimposed and coupled to form a large-scale storage and permeability system with a fracture-pore network. However, the reservoir properties and fracture development patterns of different internal fault structures remain unclear, which constrains further breakthroughs in oil and gas exploration in this area. In this study, multiple data was comprehensively utilized, including geological, geophysical, and imaging logging data. Based on core observations, well logging interpretation, and detailed structural analyses, faults in the Xujiahe Formation of the Tongjiang-Malubei area were systematically classified, and the internal structural characteristics and fracture development patterns of different types of faults were investigated. Faults in the Xujiahe Formation of the study area were widely developed and could be divided into three categories: source-connecting faults, reverse reactivated faults, and associated faults. The internal fault structures mainly include three zones: slip fracture zones, active hanging wall-induced fracture zones, and passive footwall-induced fracture zones. These zones exhibited distinct structural characteristics and strong heterogeneity. The fracture development level and storage and permeability properties of different fault types and their internal structures showed significant differences. The active hanging wall-induced fracture development zones of reverse reactivated faults were the main target areas for current fault-fracture reservoir exploration. The active hanging wall-induced fracture development zones of source-connecting faults, the passive footwall-induced fracture development zones of reverse reactivated fractures, and the slip fracture zones possessed potential for further exploration. This study provides new insights for achieving exploration breakthroughs in tight sandstone gas reservoirs and for further developing the theoretical framework of fault-fracture reservoirs in the Tongjiang-Malubei area.