Numerical Investigation of Hydrate Heterogeneity on Depressurization-Induced Production Performances and Geological Responses in the Shenhu Area, South China Sea

As a promising clean energy resource, the industrial development of deep-water natural gas hydrate still encounters numerous challenges, particularly regarding the impact of hydrate heterogeneity on production performances and geological responses. The heterogeneous characteristics of hydrate-bearing sediments fundamentally affect the reliability and adaptability of production predictions and development strategies. This study innovatively constructs the hydrate-related geological models of homogeneous, locally heterogeneous, and layered heterogeneous reservoirs according to the first hydrate production test (2017) in the Shenhu Area, South China Sea and numerically analyzes the effects of hydrate heterogeneity on long-term depressurization-induced production performances and geological responses. Modeling and simulation results indicate that the layered heterogeneous reservoirs exhibit superior production performances with higher gas production and lower water production compared with the homogeneous and locally heterogeneous reservoirs. During the depressurization-induced production, the propagations of pressure and temperature reductions display symmetrical funnel-shaped distributions in homogeneous reservoirs, while these manifest as irregular, finger-like variations in the locally and layered heterogeneous reservoirs. Notably, the underlying free gas layer acts as a crucial pathway that effectively facilitates hydrate dissociation from the gas-hydrate interlayer to the overlying hydrate sediments. The heterogeneous hydrates promote the development of gas-dominant pathways, which can significantly improve the gas production efficiency and simultaneously suppress the water output in the reservoirs. Furthermore, sensitivity analysis results indicate that high long-term stable gas production is typically favored in highly permeable layered heterogeneous reservoirs and free gas layers with high gas saturation. These findings can provide theoretical guidance for optimizing the heterogeneous reservoir target and production development of the hydrate resources.