Numerical Simulation on the Influence of Underlying Free Gas on Hydraulic Fracturing in Low-Permeability Gas Hydrate Deposits

With the continuous growth of world energy demand and the necessity of energy conservation and carbon reduction in the current environment, the efficient development of clean energy is urgently needed. As one of the most promising alternative energy sources, low-permeability hydrate deposits with different occurrence characteristics are widely distributed around the world. Reservoir stimulation exhibits different adaptabilities to various classes of hydrate deposits. Among them, there is a free gas layer under the hydrate layer in the Class I hydrate reservoir. Unlike the Class II and Class III hydrate deposits, there is a lower free gas layer during the depressurization development of the Class I hydrate deposit, which provides a second gas source for methane extraction. Based on identical basic geological parameters, this study uses an embedded discrete fracture model combined with complex fracture morphology to conduct numerical simulation research on reservoir stimulation. The influence and corresponding mechanism of the underlying free gas and water layers on the reservoir stimulation depressurization development were revealed. The sensitivity of various geological and fracture parameters to reservoir stimulation depressurization was clarified. Therefore, the feasibility and economy of different classes of hydrate reservoir stimulation were evaluated, and the advances in Class I hydrate reservoir stimulation were clarified. The results provide a theoretical basis and technical support for the field selection and scheme design of hydrate reservoir stimulation.