Numerical investigation on fluid migration effects during depressurization production of natural gas hydrate reservoir with underlying gas.

This article focuses on the effects of fluid migration from the underlying gas layer (UGL) on the physical, mechanical, and production characteristics of natural gas hydrate reservoirs during depressurization production. Using a multi-field coupled numerical model based on geological data from the SH2 site in the Shenhu Sea, South China Sea, the study simulates 360 days of depressurization with a horizontal well to analyze fluid migration behaviors, including gas and water flow from the UGL and surrounding layers. Results indicate that fluid migration from the UGL enhances gas production by promoting hydrate decomposition and downward advancement of the decomposition front, while also causing increased water production and reservoir uplift near the reservoir bottom. The study finds that increasing UGL permeability significantly improves long-term gas production rates, suggesting permeability enhancement as a potential strategy to optimize hydrate reservoir exploitation.