Experimental Analysis of CO₂ Injection on Permeability of Vuggy Carbonate Aquifers

Reactions of CO₂ with formation rock may lead to an enhancement in the permeability due to rock dissolution, or damage (reduction in the core permeability) because of the precipitation of reaction products. The reaction is affected by aquifer conditions (pressure, temperature, initial porosity, and permeability), and the injection scheme (injection flow rate, CO₂:brine volumetric ratio, and the injection time). The effects of temperature, injection flow rate, and injection scheme on the permeability alteration due to CO₂ injection into heterogeneous dolomite rock is addressed experimentally in this paper. Twenty coreflood tests were conducted using Silurian dolomite cores. Thirty pore volumes of CO₂ and brine were injected in water alternating gas (WAG) scheme under supercritical conditions at temperatures ranging from 21 to 121 °C, and injection rates of 2.0–5.0 cm³/min. Concentrations of Ca⁺⁺, Mg⁺⁺, and Na⁺ were measured in the core effluent samples. Permeability alteration was evaluated by measuring the permeability of the cores before and after the experiment. Two sources of damage in permeability were noted in this study: (1) due to precipitation of calcium carbonate, and (2) due to migration of clay minerals present in the core. Temperature and injection scheme don't have a clear impact on the core permeability. A good correlation between the initial and final core permeability was noted, and the ratio of final permeability to the initial permeability is lower for low permeability cores.