Salt Precipitation‐Driven Rock Failure Mode Transition During Geological CO2 Sequestration

Abstract

Salt precipitation has emerged as a critical factor affecting injectivity, reservoir stability, and the potential to trigger near-wellbore microseismic activity during geological CO
₂ sequestration. While previous studies have primarily focused on the brine acidification induced by CO
₂ injection, triggering geochemical reactions in carbonate rocks and leading to mechanical degradation, the mechanical behavior associated with salt precipitation in drying zones, particularly the failure mechanisms, remains poorly understood. In this work, we designed a reservoir-condition displacement system to mimic near-wellbore drying process and further investigated the rock failure modes due to salt precipitation in red sandstone samples. Our study demonstrates that, despite the densification of the pore structure due to salt precipitation, the overall mechanical performance of the rock undergoes significant deterioration. More importantly, for the first time, we observe a distinct transition of failure mode from shear-to tensile-dominated under uniaxial compression. Microstructural analysis further shows that the growth of polycrystalline and bulk crystals induces microcrack initiation and propagation, with the failure mechanism of rocks subjected to salt precipitation primarily characterized by intercrystalline damage at weak bonding interfaces under external loading.