Gas and Water Relative Permeability in THF Hydrate-Bearing Berea Sandstone

Two-phase (pore liquid and gas) relative permeability through gas hydrate-bearing sediments (HBSs) is probably the most critical property to understand gas production from natural reservoirs, as both the gas released from hydrate dissociation and pore liquid flow toward the well. Accurate estimations of the relative permeability for gas and water in HBSs and its dependence on hydrate saturation are vital for predicting the productivity of hydrate reservoirs. However, the lack of experimental data and the challenges in conducting multiphase flow experiments in HBSs have hindered precise estimations. In this study, novel apparatus was developed to measure the relative permeability of nitrogen gas (N-2) and water in tetrahydrofuran (THF) hydrate-bearing Berea sandstone core samples. The gas-water relative permeability was determined at reservoir conditions for varying hydrate saturations, specifically 0, 10, 30, 50, and 80%, in the same Berea sample. Our findings demonstrate that water relative permeability increases, while gas relative permeability decreases with increasing water saturation. Furthermore, higher hydrate saturation within Berea sandstone pores reduces the relative permeability for both gas and water, with a more pronounced relative reduction observed for higher water saturations. Numerically, water relative permeability is approximately 2 orders of magnitude higher than gas relative permeability across different hydrate saturation conditions. Moreover, the influence of hydrate saturation on gas relative permeability is more significant compared to that of water relative permeability. According to the fitting results, the relative permeability curve in our study cannot fit well the current models (Brooks-Corey model and van Genuchten model), but our experimental data are in good agreement with existing research on the order of magnitude. The experimental error of relative permeability results mainly depends on the differential pressure. The limitations of this experiment are mainly reflected by steady-state methods and the hydrate saturations. These results provide valuable insights into the relative permeability behavior in HBSs and contribute to a better understanding of the hydrate reservoir productivity.