Capillary controls on methane hydrate distribution and fracturing in advective systems

Abstract

[1] We simulate 1-D, steady, advective flow through a layered porous medium to investigate how capillary controls on solubility including the Gibbs-Thomson effect in fine-grained sediments affect methane hydrate distribution in marine sediments. We compute the increase in pore fluid pressure that results from hydrate occluding the pore space and allow fractures to form if the pore fluid pressure exceeds a fracture criterion. We apply this model to Hydrate Ridge and northern Cascadia, two field sites where hydrates have been observed preferentially filling cm-scale, coarse-grained layers. We find that at Hydrate Ridge, hydrate forms in the coarse-grained layers reaching saturation of 90%, creating fractures through intervening fine-grained layers after 2000 years. At northern Cascadia, hydrate forms preferentially in the coarse-grained layers but 2 × 105 years are required to develop the observed hydrate saturations (∼20%–60%), suggesting that hydrate formation rates may be enhanced by an additional source of methane such as in situ methanogenesis. We develop expressions to determine the combinations of sediment physical properties and methane supply rates that will result in hydrate-filled coarse-grained layers separated by hydrate-filled fine-grained layers, the conditions necessary to fracture the fine-grained layers, and the conditions that will lead to complete inhibition of hydrate formation as pore space is constricted. This work illustrates how sediment physical properties control hydrate distribution at the pore scale and how hydrate distribution affects fracturing behavior in marine sediments.