Effect of hydrate distribution on effective permeability of hydrate-bearing sediments

Abstract

Hydrate distribution influences the gas-water flow capacity and thus hydrate production in the hydrate-bearing sediments. The effective permeability is a key parameter to evaluate hydrate production capacity. However, few laboratory studies are focused on the effect of hydrate distribution on the effective permeability in the hydrate-bearing sediments. Thus, the water-phase effective permeability of nine hydrate-bearing samples prepared in a large-scaled pressure vessel under the excess-water setting was measured. The changes of pressure drop, temperature, and the electrical resistance during the measurements were analyzed. The measured and predicted effective permeability were compared. Afterwards, the heterogeneity of hydrate distribution was represented by the net increase of the electrical resistance (NIR) and its variation coefficient (VNIR) to define its effect on the effective permeability. The results showed that water flow channel change for the fresh hydrates caused the averaged pressure drop difference of 39.73 kPa in the repeated measurements. Hydrate dissociation for water flow impacted permeability measurements little. Moreover, the heterogeneous hydrate distribution, instead of hydrate saturation and pore habits, was found to cause a large deviation between the measured and predicted effective permeability. In the sample with hydrate saturation of 3.92%–8.01%, hydrates were mainly distributed at some local position. The corresponding effective permeability had a larger randomness because of the severer heterogeneity. Besides, as hydrate saturation was less than 19.46%, heterogeneity degree changes were opposite to the effective permeability changes. Instead, hydrate distribution impacted the effective permeability little. This work is beneficial to understand the physical properties of the hydrate-bearing sediments.