A simulation study of formation permeability as a function of methane hydrate concentration

Abstract

We modeled and studied the permeability of methane hydrate bearing formations as a function of methane hydrate concentration by artificially varying the T 2 distribution as well as using a tube-sphere model. We varied the proportion of irreducible and movable water as well as the total porosity associated with the T 2 distribution and found the normalized permeability as a function of methane hydrate concentration is dependent of these variations. Using a tube-sphere model, we increased the methane hydrate concentration by randomly placing methane hydrate crystals in the pore spaces and computed the permeability using either the Schlumberger T 2 relaxation time formula or a direct calculation based on Darcy’s law assuming Poiseuille flow. Earlier experimental measurements reported in the literature show there is a methane hydrate concentration range where the permeability remains relatively constant. We found that when the Schlumberger T 2 relaxation time formula is used the simulation results show a curve of normalized permeability versus methane hydrate concentration quite close to that predicted by the Masuda model with N = 15. When the permeability was directly calculated based on Darcy’s law, the simulation results show a much higher normalized permeability and only show a trend consistent with the experimental results, i.e., with a permeability plateau, when the methane hydrate crystals are preferentially placed in the tubes, and the higher the preferential probability, the larger the range where the permeability has a plateau.