Characteristics and modeling of natural fractures under compressive stress field: a case study of the eighth member of the upper paleozoic shihezi formation in southern Sulige

Abstract This study focuses on the natural fracture system in the tight, low-porosity, and low-permeability He 8 Member of the Shihezi Formation in the southern Sulige Gas Field, exploring fracture development characteristics, spatial distribution, and gas–water two-phase seepage behavior. The low porosity (6.9% to 13.9%) and low permeability (0.146 to 0.570 mD) of the reservoir, combined with the lack of core and imaging log data, limits the quantitative characterization of the fracture system and the precise development of the reservoir. To overcome these challenges, this study integrates geological analysis, well logging interpretation, rock mechanics experiments, and three-dimensional geological modeling to simulate the spatial distribution and geometry of natural fractures. The results indicate that natural fractures in the study area are primarily high-angle oblique fractures, with a predominant NNE-SSW orientation. Rock mechanics experiments show that lithology and confining pressure play key roles in fracture propagation. Additionally, simulations based on the Discrete Fracture Network (DFN) model reveal that fractures are the primary fluid flow pathways, with flow velocities within fractures significantly higher than in the matrix, thus enhancing overall seepage capacity of the reservior. The study also identifies the main controlling factors of fracture development, including tectonic stress, lithological differences, and diagenesis. This research provides important theoretical support and technical solutions for the efficient development of tight, low-porosity and low-permeability gas reservoirs.