Design of Carbon Dioxide Storage in a North Sea Aquifer Using Streamline-Based Simulation

Abstract

Abstract We propose a carbon storage strategy where CO2 and brine are injected into an aquifer together followed by brine injection alone. This renders 80-95% of the CO2 immobile in pore-scale (10s μm) droplets in the porous rock; over thousands to billions of years the CO2 may dissolve or precipitate as carbonate, but it will not migrate upwards and so is effectively sequestered. The CO2 is trapped during the decades-long lifetime of the injection phase, reducing the need for extensive monitoring for centuries. The method does not rely on impermeable cap rock to contain the CO2; this is only a secondary containment for the small amount of remaining mobile gas. Furthermore, the favorable mobility ratio between injected and displaced fluids leads to a more uniform sweep of the aquifer leading to a higher storage efficiency than injecting CO2 alone. This design is demonstrated through the incorporation of a recent model of trapping and relative permeability hysteresis based on pore-scale modeling into a field-scale streamline-based simulator. One-dimensional results are verified through comparison with analytical solutions. Results are then shown for storage in a North Sea aquifer. We design injection to give optimal storage efficiency and to minimize the amount of water injected; for the case we study injecting CO2 with a fractional flow between 85 and 100% followed by a short period of chase brine injection gives the best performance.