Kinetics of carbonate dissolution and its effects on the porosity and permeability of consolidated porous media

Abstract

Abstract Injection of carbon dioxide into carbonate oil reservoirs is expected to promote chemical dissolution of the rock and alter its petrophysical properties. This work reports an experimental investigation on porosity and permeability alterations of carbonate samples due to the acid action of the carbonated water produced by means of solubilization of carbon dioxide in an aqueous solution. Travertine marble rocks with properties similar to Brazilian pre-salt reservoir rock were used in the tests at 9000 psi and 65 °C. Dissolution was carried out in high-pressure vessels during a total period of 240 h. Reaction was stopped at intermediate time intervals to evaluate porosity, permeability and mass loss of the samples. Results showed that the dissolution reaction between the travertine and carbonated water presents a slow kinetic, leading to a small loss of 0.2 g of sample after 240 h of reaction. However, the minor mass loss impacts strongly on the porosity and permeability of the rock. Data show that a variation of 1 wt.% on the sample mass caused by dissolution produces a change of 50% on the sample porosity and of 180% on the sample permeability. The dissolution rate is greatly faster if carbonated water is replaced by HCl aqueous solution and depends on the acid solution concentration. In addition, results lead to an exponential model that allows forecasting the mass loss as a function of time. Knowledge on the dissolution rate of carbonate samples by carbon dioxide solutions is required in EOR and CO2 storage projects to estimate the changes on the flow properties of the porous formation and the damages that can be impinged to the rock.