Numerical analysis of the gas recovery performance in hydrate reservoirs with various parameters by stepwise depressurization

Natural gas hydrates have drawn worldwide attention as a significant clean energy source in the 21st century. Depressurization is known to be the most effective method for hydrate exploitation owing to its feasibility and economic benefits. Recently, stepwise depressurization has received extensive attention owing to its advantages of effective prevention of ice generation and hydrate reformation during gas recovery. In this work, we optimized the 2-D simulator to model the evolution of temperature, pressure, hydrate saturation, and gas production behavior in hydrate sediments during decomposition process via stepwise depressurization. The effect of various reservoir characteristics on gas production was analyzed by introducing the sensitivity factor. The results demonstrated that higher specific heat capacity of the reservoir would promote gas production in the early stage of the reaction; however, this effect is reversed in the later stage. A higher thermal conductivity of the hydrate cores can dramatically enhance the gas production rate; however, this advantage is weakened with increasing thermal conductivity. Reducing the gas relative permeability hinders the hydrate decomposition process, and the water relative permeability has minimal effect on gas production. Based on the sensitivity analysis, the thermal conductivity and gas relative permeability are the main factors affecting hydrate decomposition.

Automated summary

This study optimized a 2-D simulator to model the evolution of temperature, pressure, hydrate saturation, and gas production behavior in hydrate sediments during the decomposition process via stepwise depressurization. The analysis showed that the specific heat capacity, thermal conductivity, and gas relative permeability are the main factors affecting hydrate decomposition.