Abstract: The formation of ice phase during the exploitation of natural gas hydrates in permafrost regions increases the difficulty of gas migration within the reservoir. Therefore, enhancing gas production and reducing ice formation to alleviate the blockage of gas migration in the reservoir are key issues for the efficient development of frozen-thawed hydrate reservoirs. Based on the reservoir parameters of the Well DK-2 in the Qilian Mountain permafrost region, this paper proposes a combined development strategy of depressurization and hydraulic fracturing. Through numerical simulation, the influence of the fracture radius (0~5 m) and permeability (1~1 000 mD) on the exploitation effect is systematically evaluated. The research shows that the modified reservoir area formed by hydraulic fracturing can effectively inhibit ice phase blockage and accelerate pressure transmission and gas migration. When the fracture radius increases from 0 m to 5 m, the cumulative gas production over 30 years increases by 219%, with a contribution rate of 54.8% in the first 10 years, and the overall reservoir decomposition rate is 48.7%. The parameter sensitivity analysis indicates that the production enhancement effect slows down when the fracture permeability exceeds 100 mD, and the optimal fracture radius is recommended to be 4 m. This research provides a theoretical basis for the engineering control of ice plugging effects in permafrost hydrate exploitation and reveals the significant role of reservoir modification in improving the efficiency of two-phase gas and water migration.

Key words: gas hydrates, fracturing technology, freeze-thaw reservoir, numerical model, Qilian Mountain permafrost region