Pore matrix dissolution in carbonates: An in-situ experimental investigation of carbonated water injection

Carbonate rocks in underground formations are major targets for oil extraction and carbon storage. The solid part of these porous rocks contains certain minerals, such as calcite and dolomite, that can interact with aqueous solutions. Interactions could be reactive, which leads to the dissolution of these minerals. In this study, we investigated the evolution of carbonate rock dissolution during the flow of carbonated water in pores that initially contain both oil and brine. Carbonated water is an aqueous solution enriched with carbon dioxide (CO2); hence, it is acidic. In our experiments, we observed that the reactive flow and transport of carbonated water is characterized by two distinct periods. The first is a pre-dissolution period where the CO2 molecules diffused from the flowing carbonated water into the oil causing it to swell. As separate oil globules swelled, they reconnected and moved in the direction of the flowing water toward the outlet of the rock sample. In the second stage, significant mineral dissolution occurred creating wormholes that had either a conical or a dominant pattern. The pattern and extent of dissolution was dependent on the flow rate of the carbonated water and its CO2 concentration.