CCS is a well-studied technology to efficiently reduce anthropogenic CO_2 from the atmosphere, which is believed to be one of the main factors contributing to global warming. In this paper, we investigate possible changes in the mechanical properties of a shale caprock, when in contact with injected CO_2. Through diffusion, and concentration gradient, the injected CO_2 mixes with the caprock pore fluid, modifying its pH from basic to acid. Different experiments are performed to demonstrate the effect of CO_2 on mechanical properties of the North Sea Draupne shale caprock. The sample was exposed to CO_2-sat brine for about 20 days under a confining pressure of 20 MPa and a pore pressure of 10 MPa. The poroelastic properties such as Young's modulus, Poisson's ratio, bulk modulus as well as the strength were then measured. Even if a slight increase is observed on the strength, this early-age effect of CO_2 on Draupne shale seems very little and is within the experimental error. The results of P-wave velocity measurements reveal a possibility that CO_2 may be coming out of solution during the test. In order to address this possibility, the experimental conditions are being reviewed and continuous measurements (every minute) of Young's modulus and Poisson's ratio are performed onthe sample from consolidation to failure, through the flowing of CO_2-undersaturated brine.
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