Relative water and gas permeability for gas production from hydrate-bearing sediments

Relative water and gas permeability equations are important for estimating gas and water production from hydrate-bearing sediments. However, experimental or numerical study to determine fitting parameters of those equations is not available in the literature. In this study, a pore-network model is developed to simulate gas expansion and calculate relative water and gas permeability. Based on the simulation results, fitting parameters for modified Stone equation are suggested for a distributed hydrate system where initial hydrate saturations range from S_h=0.1 to 0.6. The suggested fitting parameter for relative water permeability is n_w≈2.4 regardless of initial hydrate saturation while the suggested fitting parameter for relative gas permeability is increased from n_g=1.8 for S_h=0.1 to n _g=3.5 for S_h=0.6. Results are relevant to other systems that experience gas exsolution such as pockmark formation due to sea level change, CO₂ gas formation during geological CO₂ sequestration, and gas bubble accumulation near the downstream of dams. Key Points Fitting parameters for Stone equation are suggested for gas production Stone equation can be used with appropriately chosen parameters Fitting parameters for gas permeability depend on hydrate saturation