Gas recovery from marine hydrate reservoir: Experimental investigation on gas flow patterns considering pressure effect

Accurate acquisition of fluid flow patterns is crucial for economic exploitation and production prediction of hydrate-bearing sediments (HBSs). In this study, the clayey-silt marine sediments obtained from the South China Sea are used to remold core to investigate the effects of hydrate saturation, effective stress, pore pressure and osmotic pressure on the gas flow patterns. The results indicate that when the hydrate saturation is increased from 24.73% to 48.34%, the gas flow transitions from viscous flow to slip flow, and the gas slippage effect gets more and more pronounced with increasing hydrate saturation. The increase in effective stress leads to an increased sensitivity of gas permeability to changes in osmotic pressure, and it is more obvious at lower hydrate saturation. Elevated pore pressure leads to a small decrease in gas permeability but does not alter the flow pattern of fluid flow in the marine sediment. In addition, reducing the osmotic pressure can effectively weaken the slippage effect. Viscous flow and slip flow control the type of gas flow in HBSs, but slip flow dominates. Finally, a semi-empirical permeability model that considers the effect of hydrate saturation and effective stress on gas permeability is fitted with experimental data.