Design of Foam-assisted Carbon Dioxide Storage in a North Sea Aquifer Using Streamline-based Simulation

Carbon capture and storage (CCS) − the collection of CO2 from industrial sources and its injection underground − could potentially contribute to the reduction of atmospheric emissions of greenhouse gases. In this paper, we investigate the sequestration of CO2 in aquifers with the co-injection of surfactants for foam generation, to allow increased storage capacity. This is equivalent to the use of foam for conformance control in enhanced oil recovery applications. To study foam-assisted sequestration, we extend an in-house streamline-based simulator. We use two foam models: Hirasaki and Lawson (1985) and Rossen et al. (1999). In both models foam hinders gas mobility through increasing its apparent viscosity. The modified simulator is validated by comparison to analytical solutions. We then investigate the performance of CO2 sequestration with the co-injection of surfactants. We look at CO2 sequestration in a North Sea aquifer. We study both simultaneous and alternating surfactant-gas injection at different fractional flows (i.e. water:gas ratios). For cases where a seal provides a reliable trapping mechanism, the simulation results suggest that the use of surfactants to generate foam significantly improves the storage efficiency at a marginal increase in water consumption. In this setting, CO2/surfactant simultaneous injection at a 0.5 CO2 fractional flow was found to be the optimum injection strategy for the case investigated. If the seal is unreliable or absent, CO2/brine simultaneous injection at a 0.85 CO2 fractional flow was found to be the optimum injection strategy. Although foam-assisted sequestration in this case furthers improve the storage efficiency, it does so at a significant increase in water consumption. This is since, although foam generation improves the sweep during the sequestration phase, it significantly hinders the sweep during the chase brine injection phase. Based on that, having a design where the surfactant will degrade just before or during the chase brine injection phase would provide the optimum sequestration strategy—without reliance on the presence or integrity of the seal.