Abstract
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.
Highlights
Carbon Capture and Sequestration (CCS) is one of the many solutions to limit the current global warming [1]
For quantitative analysis and visualizations, various methods can be used such as X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), etc
Caprocks have permeabilities reduced by six orders of magnitude or more compared with the permeability in the reservoir zone. This is due to the fact that caprocks are made of fine grains such as clay particles, and/or they have been subjected to specific diagenetic processes such as dissolution/ recrystallization and cementation
Summary
Carbon Capture and Sequestration (CCS) is one of the many solutions to limit the current global warming [1]. Low permeability formations acting as barriers have been studied in detail for nuclear waste storage purposes, and in this case, the scientific issues are very similar [5, 6] the time scales are larger for nuclear waste problems and perfect confinement is required. Linking these two problems may be confusing in terms of communication and public acceptance.
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