6 - Carbon dioxide (CO2) injection design to maximise underground reservoir storage and enhanced oil recovery (EOR)

Abstract

We propose designs for CO2 injection to maximise storage in aquifers and to maximise both CO2 storage and enhanced oil recovery (EOR) in oil reservoirs. A review of simulation and experimental studies suggests a carbon storage strategy where CO2 and brine are injected into an aquifer together followed by brine injection alone. Based on simulation studies, this can render 80–95% of the CO2 immobile in pore-scale droplets within the porous rock. The method does not rely on an impermeable cap rock to contain the CO2; furthermore, the favourable mobility ratio between injected and displaced fluids leads to a more uniform sweep of the aquifer leading to higher storage efficiency than injecting CO2 alone. We then consider CO2 storage in oilfields. We propose to inject more water than the traditional optimum that maximizes only oil recovery. This causes the CO2 to remain in the reservoir, increases the field life and leads to improved storage of CO2 as a trapped phase. Again, a short period of chase brine injection at the end of the process traps most of the remaining CO2.