oa The Impact of CO2 on Electrical Rock Properties - Laboratory Experiments with Regard to Carbon Capture and Storage

CO2 sequestration needs reliable monitoring techniques. Electromagnetics provides a promising new approach because the electrical conductivity is a sensitive indicator for CO2 migration in saline aquifers. However, the influence of CO2 on rock conductivity is still insufficiently known. Therefore, we have developed an experimental set-up which allows investigating electrical characteristics of the injection process as well as the impact of dissolution on pore water conductivity. When CO2 dissolves in the pore water dissociation processes can double the pore water conductivity. This is quantified by an adaptation of the laws of Archie and Waxman & Smits, respectively. Data and adaption formulation are confirmed by combined geochemical-geoelectrical simulations. Furthermore, water-saturated sand samples were investigated while CO2 displaced the pore water at pressures up to 13 MPa and temperatures up to 40°C. A decrease in electrical conductivity by a factor of up to 33 corresponds to a residual water saturation of 14 to 19%. This decrease has also been demonstrated under supercritical conditions. As an integrative interpretation, a conceptual model of electrical rock properties during CO2 sequestration is presented.