Gas Phase Permeability of CO₂ Hydrate-Bearing Silty-Clayey Sediments

Abstract

Hydrate-based CO 2 sequestration (HBCS) in marine sediments is an effective method for mitigating global climate change driven by energy consumption. The permeability characteristics of the CO 2 hydrate-bearing sediments are key indicators for evaluating injection rates and reservoir sealing integrity. As the primary low-permeability lithology in marine sediments, silty-clayey sediments provide superior sealing integrity. However, the relative research on gas phase permeability of CO 2 hydrate-bearing silty-clayey sediments still remains limited. Thus, a bespoke seepage experiment platform was independently developed in this study, and the effects of hydrate saturation and effective axial stress on the permeability evolution of CO 2 hydrate-bearing silty-clayey sediment as well as the impact on sediment permeability caused by hydrate formation and dissociation were examined. The results indicate that increasing initial water saturation raises the resistance of sediments to CO 2 gas flow, which is also influenced by CO 2 dissolution and adsorption. In silty-clayey sediments, increasing water saturation from 10% to 35% results in a substantial reduction in gas phase permeability─by approximately 79.69%. In contrast to sandy sediments, the gas phase permeability of CO 2 hydrate-bearing silty-clayey sediments exhibits a nonlinear trend with increasing hydrate saturation─initially rising, then declining, and subsequently increasing again. Axial stress compresses the pore space and throat size of silty-clayey sediments, resulting in a reduced gas phase permeability. At a hydrate saturation of 24.96%, the permeability of silty-clayey sediments under an effective axial stress of 3 MPa is reduced by approximately 94.72% compared to that of unconsolidated sediments. In addition, hydrate dissociation leads to a reduction in sediment permeability, and this reduction becomes more pronounced as the hydrate saturation rises.

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