Transport properties of hydrate bearing formations from pore-scale modeling

Gas hydrates are an attractive source of energy as natural gas can be produced from these deposits by depressurization or thermal stimulation. Empirical correlations developed in hydrology and petroleum engineering have been used for describing transport properties of sediments containing gas hydrates in hydrate simulators. The goal of this work is to estimate the transport properties of hydrate-bearing sediments from pore-scale modeling. Sediment particles have been packed using a discrete element method and pore radius distribution is calculated using Delaunay triangulation. Hydrate deposition is modeled in a single pore to develop pore-scale laws of hydrate occupancy. Pore radius distributions are recalculated after hydrate deposition. Percolation theory is used to numerically calculate effective transport properties of the medium at different saturations. Pore-scale models showed that the hydrates form at the pore walls if deposited from the flow of methane-saturated water alone. The saturation of hydrate deposited in different size pores was found to be uniform. A Gaussian distribution of particle size of the sediment results in a Rayleigh distribution of pore throat radius. As the variance of the particle size increases, so does the width of the pore size distribution. As the hydrate saturation increases, the permeability of the sediment decreases. This decrease follows Civan's correlation with a β of 0.75. The relative permeability becomes increasingly dependent on water saturation as the hydrate saturation in the sediment increases. A new correlation for relative permeability is developed by matching the percolation theory estimates.