Fractal insights into permeability control by pore structure in tight sandstone reservoirs, Heshui area, Ordos Basin

Abstract Tight sandstone reservoirs, characterized by low porosity and permeability, have long posed significant challenges for oil and gas exploration and development. This study focuses on the reservoirs in the Chang 6–Chang 8 section of the Yanchang Formation, located in the Heshui area of the Ordos Basin. These reservoirs, with their complex pore structures and diverse genesis, represent typical examples of tight sandstone reservoirs. The primary aim of this study is to systematically investigate the pore structures of these reservoirs, elucidating the mechanisms that govern permeability and thereby providing a scientific basis and technical support for the efficient development of tight sandstone oil and gas resources. Utilizing high-pressure mercury injection and nuclear magnetic resonance techniques, the study emphasizes the crucial role of pore fractal properties in controlling reservoir permeability. The results indicate that the complexity of pore structures directly influences both permeability and mobile fluid saturation. Specifically, smaller pores exhibit lower fractal dimensions, while larger pores show higher fractal dimensions, with significant impacts on both permeability and mobile fluid saturation. Additionally, the study examines the effects of different sedimentary facies and diagenetic stages on the pore structures of sandstone reservoirs. The findings reveal distinct evolutionary patterns of pore structures across various depositional environments within the braided river delta system. Furthermore, diagenetic processes and cementation play essential roles in shaping the diversity of pore structures in these reservoirs. In conclusion, this study offers new insights into the relationship between pore structure and permeability in tight sandstone reservoirs, providing valuable theoretical guidance for the exploration and development of oil and gas resources.