Experimental investigation in the permeability of methane hydrate-bearing fine quartz sands

The permeability is one of the intrinsic parameters that determines the fluid flow in the porous media. The permeability in hydrate-bearing sediments affects the gas recovery and production of hydrate reservoirs significantly. The irregular permeability characteristics are challenging for fine-grained hydrate-bearing sediments. In this study, a series of experiments was conducted using an one-dimensional pressure vessel to investigate the hydrate formation characteristics and the permeability in hydrate-bearing fine quartz sands (volume weighted mean diameter was 36.695 μm). Hydrate saturations (0–26% in volume) were controlled and calculated precisely based on the amount of injected water and gas, the system pressure and temperature. The results indicated that the hydrate nucleation induction period was completed during gas injection, and the average time of hydrate formation was within 500 min. The permeability of methane hydrate-bearing fine quartz sands was investigated by steady gas volume flow. For hydrate saturation lower than 13.94%, the hydrate mostly formed in grain-coating, the permeability reduction exponent calculated by Parallel Capillary, Kozeny Grain Coats and Simple Cubic Filling models were 2.00, 2.10 and 1.74 respectively, and Simple Cubic Filling model was in accordance with the experimental data best. However, for hydrate saturation ranged from 13.94% to 25.91%, the permeability increased due to the flocculation structure formation of fine quartz sands and hydrate, which caused the increase of effective porosity. A new relationship among hydrate saturations, effective porosity, the ratio of permeability in the presence and the absence of hydrate was developed. This study developed the mathematical models for predicting the permeability with hydrate saturation in fine quartz sands, which could be valuable for understanding the characteristics of hydrate-bearing fine-grained sediments.