Investigation of porosity and permeability effects from microstructure changes during limestone dissolution

We studied experimentally the dissolution of a porous limestone core during CO2‐enriched water injection. We measured the changes in porosity and permeability arising from modifications of the pore network geometry and the fluid‐rock interface. A methodology based on periodic X‐ray microtomography imaging was implemented to record the evolution of the time‐ and scale‐dependent microstructures with a spatial resolution of 4.91 μm. Two processes were successively involved in the rapid permeability increase of the sample, as documented from microscale to core‐scale measurements. First, the microcrystalline phase was partially dissolved, associated with displacement of mineral particles. During this process, the exponent n of the power law k ∼ ϕn decreased continuously. Secondly the sparitic phase dissolved, accompanied by a decrease of the pore wall roughness and an increase of the pore connectivity. This second period was characterized by a constant value of n. The reactive surface decreased noticeably during the transition from the microcrystalline to the sparitic dissolution periods, whereas the effective porosity increased strongly.