Methane recovery from gas hydrate-bearing sediments: An experimental study on the gas permeation characteristics under varying pressure

In this paper, characteristics of gas permeation through gas hydrate-bearing sediments were explored under varying differential pressure for three types of sedimentary core samples, including 100 wt % silica sand, 95 wt % silica sand +5 wt % montmorillonite clay, and consolidated sandstone using a standard core-holder. Results of the experiments indicate that capillary breakthrough, hydrate-forced heave or agglomeration and also Klinkenberg effect play important roles in controlling the gas permeation through different porous sediments, depending on the sediment type and properties such as grain/pore size distribution and degree of consolidation. It was observed that due to the presence of large pores in unconsolidated silica sand core samples, the gas flow is dominated at both hydrate-free and hydrate-bearing cases by the capillary breakthrough mechanism rather than the gas slippage which resulted in direct relationship between the gas permeability and the differential pressure. This mechanism was also observed to be dominant while measuring the gas permeability for the hydrate-free sandstone core sample. For the unconsolidated sand-clay core samples, higher saturation of methane hydrate led to relatively higher gas permeability due to hydrate-forced heave phenomenon which pushed the sediment grains apart from each other or hydrate agglomeration that formed inter-grain pores. Klinkenberg effect became significant for the hydrate-free sand-clay and hydrate-bearing sandstone core samples; however, it was not observed to be dominant in the hydrate-bearing sand-clay core samples due to the hydrate-forced heave and agglomeration until the inlet pressure was sufficiently high.