Swelling damage characteristics induced by CO2 adsorption in shale: Experimental and modeling approaches

Carbon dioxide (CO 2 ) geological sequestration represents a critical technology in mitigating climate change. Shale reservoirs demonstrate a pronounced affinity for CO 2 , resulting in adsorption-induced swelling that significantly impacts permeability, mechanical strength, injection efficiency, and sequestration safety. For this, we tried to explore the key factors driving the swelling of shale upon CO 2 injection and its subsequent impact on reservoir properties. Utilizing a self-developed high-temperature-pressure gas adsorption apparatus, we measured strain in Jurassic shale at 308 K under constant hydrostatic pressure with helium (He) at 1300 psi (1 psi = 6.895 kPa) and CO 2 at 850 psi. Next, we investigated the influence of CO 2 concentration on swelling protentional while maintaining constant pressure, uncovering the anisotropic deformation in relation to pressure. It shows that CO 2 adsorption induces significant swelling in shale, following a Langmuir-type pressure relationship. Deformation is more pronounced perpendicular than that parallel to the bedding plane. At low pressure, vertical swelling is 2.28 times greater than the horizontal; while at high pressure, the vertical compression is 31.26 times greater than the horizontal. It seems that the anisotropic swelling enhances permeability predictions during CO 2 injection. Mixed gases under constant compression can prompt gas desorption, stress redistribution, and alterations in pore structure, amplifying He compression effect. The strain induced after replacing CO 2 with He exceeds that from pure He injection. The asynchronous response of CO 2 -induced swelling and mechanical compression can precipitate crack propagation and fracturing. Overall, anisotropic swelling from CO 2 adsorption changes pore structure and permeability, affecting fluid flow and storage. Considering CO 2 concentration and anisotropic characteristics in reservoir modeling is essential for optimizing injection strategies and enhancing reservoir efficiency.