Predicting the water permeability of hydrate-bearing quartzitic sands based on the fractal theory

The gas production efficiency from hydrate deposits is largely governed by the permeability in hydrate-bearing sediments. In the permeability prediction models used by varieties of numerical simulators, parameters with physical significances to quantitatively characterize the pore-scale changes in sediments undergoing hydrate formation and dissociation are still unavailable. In this work, fractal theory based analyses on Low-field Nuclear Magnetic Resonance (L-NMR) experimental data is applied to the hydraulic properties of hydrate-bearing sediments. Hydrate saturation dependent area and tortuosity fractal dimensions are extracted from L-NMR experimental data of methane-hydrate-bearing quartzitic sands. Then, these two fractal dimensions are further extended to establish a fractal theory based permeability model. Finally, the proposed permeability model is experimentally validated. The results show that the pore space within hydrate-bearing quartzitic sands is multi-fractal. Pore-scale hydrate behavior dependent maximum pore diameter largely governs the hydraulic property of hydrate-bearing sediments. The fractal permeability model achieves a consistent prediction with the measured permeability, and has a great potential in the economic feasibility evaluation of gas recovery from hydrate-bearing sediments.