Cement lithofacies shape permeability evolution in sandstones during CO2-rich brine injection

Microstructural evolution in cemented sandstones alters pore-throat connectivity and permeability, directly affecting CO 2 injectivity in offshore geological storage reservoirs. However, the influence of cement lithofacies on these responses remains insufficiently understood. Here, we conducted reservoir-condition displacement experiments on natural sandstone cores to investigate the evolution of porosity and permeability associated with distinct cement reaction pathways during CO 2 -rich brine injection. Our results demonstrate that cement alteration involves chemical precipitation, mineral transformation, and mechanical weakening, rather than simple dissolution alone. More importantly, distinct permeability evolution patterns were observed among the three cement lithofacies, with Fe-dolomite-cemented sandstone showing an overall increase with intermittent fluctuations, clay-cemented sandstone experiencing an initial increase followed by a continuous decline, and weakly cemented sandstone exhibiting a monotonic increase. Microstructural analysis reveals that carbonate precipitation and clay transformation contribute to pore filling and restriction of flow pathways, whereas carbonate dissolution and cement weakening promote pore enlargement and connectivity enhancement. Consequently, geochemical reactions cause the porosity–permeability relationship to deviate markedly from conventional predictive models. These findings highlight the critical role of cement lithofacies in controlling sandstone petrophysical responses during CO 2 -rich brine injection and provide insights for evaluating reservoir-scale CO 2 injectivity.