Control of Differential Tectonic Evolution on Tectonic Fractures in Different Tectonic Segments of Tight Gas Sandstone Reservoirs: Upper Triassic Xujiahe Formation, Western Sichuan Foreland Basin

In the context of complex tectonic evolution, due to the control of tectonic compression stress and faults on tectonic fractures, the formation and development of tectonic fractures in the T₃x² tight reservoirs present significant variations across different tectonic segments in the Western Sichuan Foreland Basin. We clarified the control of differential tectonic evolution on the formation and development of tectonic fractures in different tectonic segments through field-based observations, core samples, image logging, as well as fluid inclusion petrography and temperature determinations of fracture-filling materials, combined with 2D balanced cross-section restoration. The study area primarily manifests two types of tectonic fractures in the tight reservoirs: orogenrelated fractures (regional fractures) and fault-related fractures. The orientations of these fractures are predominantly E-W, nearly N-S, NE, and NW. Specifically, the northern segment area only shows the development of regional fractures, while the southern and middle segments exhibit the development of both regional and tectonic fractures. There are three phases of tectonic fractures in different tectonic segments, and their formation times are relatively consistent. The Mesozoic tectonic events had a significant impact on the northern and central segments, with the amount of tectonic shortening and the rate of stratigraphic shortening gradually decreasing from the northeast to the southwest. The compressional stress resulting from tectonic compression also decreases from the northeast to the southwest. As a result, the development of first-phase and second-phase tectonic shear fractures is more pronounced in the northern and middle segments compared to the southern segment. Under the significant control of faults, the development of N-S- and NE-oriented faultelated fractures is more pronounced in the southern segment, while the development of NE-oriented fault-related fractures is relatively higher in the middle segment. Overall, there is an increased density of fractures and an increasing trend in fracture scale from the northern to the middle and then to the southern segment.