Multiscale Petrophysical Response of Sandstone and Limestone Formations During CO2 Sequestration.

The injection of CO2 into deep geological formations induces geochemical interactions that may modify reservoir petrophysical properties and influence the long-term performance of carbon capture and storage (CCS) projects. This experimental study evaluates the effects of CO2 injection on sandstone and limestone through an integrated petrophysical and physicochemical characterization, including X-ray diffraction (XRD), computed tomography (CT), coreflooding experiments, and fluid compatibility analyses. A distinguishing aspect of this research lies in its focus on the Mugrosa Formation (Colombia), using a representative core sample (sandsotne) and a synthetic brine formulated to replicate the composition of field-produced formation water, thereby reproducing realistic reservoir conditions. Results indicate that limestone exhibited a 6% increase in porosity and a 57% reduction in permeability due to calcium mineral dissolution and the formation of preferential flow pathways (wormholes) identified by CT imaging. In contrast, sandstone showed no significant changes in porosity, permeability, or mineralogical composition following CO2 exposure. Brine analyses revealed greater CO2 dissolution at lower temperatures, promoting carbonic acid formation and enhancing mineral dissolution processes in limestone. Furthermore, CO2-oil compatibility tests showed increased oil viscosity, suggesting destabilization of heavy hydrocarbon fractions and potential asphaltene precipitation under immiscible conditions. These results demonstrate that the response of the rock-fluid system to CO2 injection is strongly controlled by mineralogical composition and suggest that sandstones are a better candidate for long-term carbon capture and storage processes, while limestones may present a greater risk of petrophysical alteration and loss of permeability.