Evaluating Sealing Efficiency of Caprocks for CO₂Storage: an Overview of the Geocarbone-Integrity Program and Results

An overview of the three-year program and results of the Geocarbone-Integrity French project is given. It focused on the development of experimental and numerical methodologies to assess the integrity of underground CO<sub>2<sub/> storage at various scales. The primary criteria in the selection of a caprock formation for CO<sub>2<sub/> storage purposes are the thickness and permeability of the formation. Local and limited migration of CO<sub>2<sub/> into the caprock due to insufficient capillary entry pressure has been studied as a probable scenario. At a large scale, caprock characterization requires at least seismic profiles to identify lateral continuity. When well-logging data are available, simple rules based on clay content can be used to estimate thicknesses. For the formation considered, the geochemical reactivity to CO<sub>2<sub/> was small, making the reaction path difficult to identify. Similarly, artificial alterations of samples representing extreme situations had little impact on geomechanical properties. Finally, with realistic overpressure due to injection, shear fracture reactivation criteria are not reached and migration of CO<sub>2<sub/> either by diffusion or by two-phase flow within the first meters of the caprock produce mostly a decrease in porosity by precipitation, and very locally an increase in porosity by dissolution.