Permeability Anisotropy of Hydrate-Bearing Sediment during Consolidation Process: Insights from CT Scanning and Pore Network Modeling

Abstract

During the initial phase of the depressurization exploitation process of natural gas hydrate, the reduction of pore pressure will cause effective stress concentration and consolidation deformation in the hydrate-bearing sediment (HBS), while the occurrence of the water-channeling phenomenon will trigger the rise of pore pressure and swelling locally in the reservoir. Evaluating the dynamic evolution process of HBS permeability is crucial for reservoir capacity. In this research, with the X-ray CT triaxial experiments and the pore network model, the permeability change characteristics in the compression and swelling processes of HBS with a saturation of 0.29 were investigated. It is found that there is a progressive decline in absolute permeability as the effective stress increases, while the capillary pressure (P c ) gradually increases, and the anisotropy of capillary pressure first rises and then diminishes; the gas relative permeability (k rg ) increases, and the water relative permeability (k rw ) decreases with the increase of effective stress during the compression process. During the swelling process, the absolute permeability and capillary pressure do not recover, whereas for unconsolidated HBS, k rg is larger and k rw is lower under the same effective stress.