Forcing gaseous CO2 trapping as a corrective technique in the case of abnormal behavior of a deep saline aquifer storage

Abstract : The large-scale development of carbon geological storage requires the safety demonstration of this technology. The European Directive on the geological storage of carbon dioxide specifies the safety strategy to be adopted. Notably, a corrective measure plan is required in order to mitigate the potential "significant irregularities". In this paper, we describe one measure that could be applied in case of an unexpected abnormal behavior of the gas plume (e.g. leakage of CO2). The objective is to trap the mobile gaseous CO2 as quickly as possible; among all the trapping mechanisms occurring after CO2 injection, capillarity trapping is the fastest and we then focused on its enhancement and improvement. The intervention strategy consists in injecting brine through the former CO2 injection well in order to accelerate the wetting of the CO2 plume. We run simulations through a 1D-axisymetric model in order to evaluate the efficiency of such a measure; the results are sensitive towards brine injection rates and other site-specific key parameters but, in any case, the measure set-up leads to a rapid immobilization of the gaseous CO2 in comparison with a simple relaxation. The consequences of the pressure build-up in terms of hydraulic and mechanic risks are not critical in the base case simulation conditions and thus do not compromise the applicability of the corrective measure.