Characterization of the Hellisheidi-Threngsli CO2 sequestration target aquifer by tracer testing

Abstract

Mineral sequestration is among several promising methods of CO2 emission reduction. It involves incorporation of CO2 into a solid phase via precipitation of carbonate minerals. A prerequisite to carbonate precipitation is the availability of aqueous metal cations and a network of porous media for fluid flow and water rock interactions. The Hellisheidi-Threngsli lava field in SW Iceland comprises ideal conditions for studying the feasibility of permanent CO2 storage as minerals in basaltic rocks. Prior to the injection, detailed information needs to be gathered to delineate the CO2 injection strategy and reservoir potential to store CO2. In heterogeneous porous aquifers, simulations and predictions of groundwater flow and solute transport require detailed knowledge of aquifer parameters and their spatial distribution. Tracer testing offers the possibility to efficiently investigate the aquifer between the injection and sampling wells and to characterize the relevant aquifer properties based on effective parameter values. Tracer tests can be performed at laboratory and field-scales with depth integrated (two-dimensional) or multilevel (three-dimensional) set-ups, and under natural or forced hydraulic gradient conditions. Both non-reactive and reactive tracer compounds can be used. This contribution reviews depth integrated and natural and forced gradient tracer test methods, their fields of application at different transport scales, the SF6 and Na-Fluorescein...