Gas permeability of frozen and hydrate-bearing sediments: experimental evidence

Permafrost has accumulated large amounts of free or hydrate natural gas. During phase changes of pore moisture, gas pressure can reach or exceed overburden pressure, allowing gas to migrate upward and potentially erupt explosively through frozen sediments. These conditions are simulated in experiments on gas flow through frozen hydrate-free and hydrate-saturated samples using a specially designed core holder. The experiments examine the permeability behavior of clay silt samples with varying pore moisture at temperatures from -10 degrees C to +1 degrees C. At temperatures below thaw point and gas pressures within 2 MPa, gas permeability increases, making almost impermeable frozen rocks permeable. A frozen sand-clay sample with forming and dissociating pore gas hydrate shows permeability correlated with relative strain and acoustic wave velocities. Under stepwise uniaxial pressure (4-10 MPa) and subsequent depressurization, hydrate-saturated samples become 39% less permeable during loading but retain this level during unloading.