Permeability impairment of a limestone reservoir triggered by heterogeneous dissolution and particles migration during CO2-rich injection

A CO2-rich brine core-flood experiment in calcite limestone for conditions representative of underground storage (P=12MPa and T=100 degrees C) was performed in order to explore the dissolution mechanisms arising at moderate CO2 partial pressure (0.3MPa). An increase of the total porosity ((T)) accompanied by a persistent permeability (k) decrease was measured. The mechanisms controlling this atypical anticorrelated k-(T) relationship were investigated from the analysis of high-resolution X-ray microtomography images of the sample acquired before and after the experiment. All the evidences converge to the conclusion that the ubiquitous decrease of permeability measured during the 44h of dissolution is due to the clogging of a fraction of the macroporosity by microporous material triggered by the rearrangement of the detached undissolved particles. This mechanism results in the development of low permeability zones bridging the macroporosity.