Numerical simulation on depressurization extraction of natural gas hydrate based on a coupled thermal–hydraulic–chemical model

Abstract

To explain the dissociation law in the depressurization extraction of natural gas hydrate (NGH), a coupled thermal–hydrologic–chemical (THC) model was established. The coupled model was confirmed through the data of Masuda’s depressurization experimentation and the first NGH extraction in the Shenhu Area. After verifying the applicability of the numerical model, a long-term (1000 days) gas productivity of the NGH reservoir at the W17 test site was explored. This paper quantitatively analyzed the effect of reservoir permeability, temperature and porosity on NGH production capacity (cumulative methane production). The results revealed that the increase in reservoir permeability and temperature could significantly enhance methane production. The subsequent NGH extractions should raise the permeability and temperature of the target hydrate reservoir. Under the same NGH saturation, cumulative methane production did not always increase with increasing reservoir porosity. When the reservoir porosity increased to 0.40, the cumulative methane production decreased with the increase in porosity. The results showed that the combined extraction approach of depressurization and thermal flow injection is more efficient than only the depressurization method.