Buried hills are basement uplifts beneath sediment layers that possess significant exploration potential. Using the Jianbei Slope of the Qaidam Basin in China as a case study, we systematically investigated the types and origins of fractures in deep buried-hill gas reservoirs. In our study, we synthesized various data, including experimental results, production dynamics, and both conventional and special logging with the aim of clarifying the sequence and effectiveness of fracture formation in these gas reservoirs; analyzing the impact of effective fractures on fluid migration, accumulation, and preservation; and proposing a development plan to enhance stable production. Research reveals that since the Late Paleozoic, the region has been influenced by multiple phases of tectonic stress, deep fluid dissolution, and surface weathering leaching. This has resulted in a fracture system dominated by east-west trending deep major faults, with accompanying tectonic fractures, alongside dissolution, diagenetic, and weathering-collapse fractures. Smaller fractures oriented at an angle to the maximum principal stress and fractures with normal stress lower than the compressive strength are conducive to maintaining fracture effectiveness. Fracture widths range from 0.1 μm to 343.36 μm, with effective fractures comprising 63.49% of the total. Based on aperture and permeability, effective fractures are categorized into three levels: Level I fractures (>100 μm) serve as primary migration pathways; Level II fractures (10–100 μm) are well configured with dissolution pores, forming a foundation for favorable reservoir development; and Level III fractures (micron scale) enhance reservoir storage capacity by connecting fractures. The gas-water interface in the reservoir rises rapidly and unevenly. In the I + II + III fracture combination model, fluid exhibits high-conductivity channeling, leading to rapid declines in formation pressure, quick water breakthroughs in single wells, and severe water sealing. Conversely, in the II + III fracture combination model, fluid invasion is characterized by weak-to-strong finger-like intrusion, leading to prolonged stable production. Vertically, the 20-m to 60-m interval above the bedrock weathering crust has a favorable pore-fracture configuration, making it a high-quality reservoir zone in buried hills. In addition, local thick layers of Level II microfractures within the bedrock represent potential exploration targets. Considering the differential distribution of reservoir fractures, the optimal development plan is expected to achieve a recovery rate of 28.35% by 2030.

You can access this article if you purchase or spend a download.