Gas Invasion Patterns in Saturated Marine Sediments

Abstract

Gas invasion into fluid-saturated marine sediments is relevant to various geophysical and environmental processes, such as the formation of gas hydrate reservoirs and their behavior during depressurization-based gas production. The link between pore-scale mechanisms and macroscopic invasion patterns as well as their governing parameters, especially under high stress and intense flux conditions, remains unclear. We study gas invasion into water-saturated marine sediments using a coupled framework of the discrete element method and pore network modeling. We show that two dimensionless numbers, the stress number Σ and the seepage number D, govern five representative gas invasion patterns of capillary fracturing, capillary invasion, viscous fingering, seepage fracturing, and the transitional morphologies among them. The capillary number C, the stress number Σ, and the seepage number D collectively determine the shear, tensile, or cavity dominated fracturing in marine sediments. The results provide a description of gas migration regime transitions in marine sediments, which can help establish a scientific foundation to explain the development of marine cold seeps in nature and to design gas hydrate exploitation strategies.