Impact of CO2-induced dissolution and salt precipitation on net changes in elastic and viscoplastic properties of chalk under near-wellbore conditions

This study investigates the impact of formation dry-out on the P-wave ( V p ) and S-wave velocities ( V s ), static elastic properties, strength, and creep of reservoir carbonates, which remain less studied than sandstone. The laboratory protocol is designed to simultaneously monitor static and dynamic geomechanical properties, providing new insights into the mechanisms governing their contrasting responses during CO 2 flooding, a phenomenon widely reported in the literature. Flow-through triaxial tests were conducted by injecting dry CO 2 into partially water-saturated plugs to mimic near-wellbore storage conditions, complemented by rock characterization techniques and geochemical modeling for data interpretation. Results show that halite precipitates continuously as water evaporates, whereas dissolution is restricted to the early injection stage due to rapid chemical equilibrium. The data also indicate that salt precipitation contributes to increased pore collapse strength and preferentially enhances static stiffness relative to dynamic stiffness. However, a transient acceleration of the creep rate is observed at the onset of injection, reflecting a mechanical weakening likely due to mineral dissolution. These contrasting responses are also reflected in the velocity measurements. During injection at high stress, salt precipitation primarily increases velocity by up to 2-3%. In contrast, comparison before and after flooding shows an enhanced stress sensitivity of V p and V s . Therefore, a decoupling in both magnitude and trend is observed between the evolution of static and dynamic properties during CO 2 flooding. Conceptual models are proposed to explain these mechanical behaviors. The experimental study highlights the importance of the relative magnitude and timing of dissolution and precipitation during storage operations, as their interplay governs the contrasting mechanical responses of static and dynamic rock properties.