Numerical simulation on natural gas hydrate depressurization production considering sediment compression effects

Sediment compression during submarine hydrate depressurization production causes changes in physical and mechanical characteristics, which in turn affects production results. In this paper, based on geological conditions of SHSC-4 well in Shenhu area, a theoretical model considering sediment compression effects is established by COMSOL, and the effects on the evolution of reservoir physical and mechanical characteristics within 60 days during depressurization production is simulated. The results show that model dimension effects can be ignored when the size l ≥ 100 m within 60 days. The effects of sediment compression on the physical characteristics of the reservoir are mainly realized by affecting the evolution of porosity, and the porosity reduction leads to permeability reduction. The larger the sediment compression coefficient, the higher the pore pressure in the reservoir. Sediment compression hinders the propagation of low pore pressure and heat transfer in the reservoir, which is unfavorable for hydrate decomposition favorable to hydrate reformation. A larger or smaller sediment compression coefficient selected in the simulation can lead to under- or over-estimate of reservoir gas production, so choosing an appropriate sediment compression coefficient when considering sediment compression is necessary for rational assessment of reservoir production behavior. In the production test site, when the production pressure is higher than 3 MPa, the pore pressure gradient is the key factor to promote gas production from the reservoir. When the production pressure is lower than 3 MPa, the sediment compression is the key factor to impede gas production from the reservoir.