Jonathan Scafidi , Stuart M. V. Gilfillan 

Co-production of methane and geothermal energy from produced subsurface brines with onsite power generation and carbon capture has been proposed as a technically feasible means to reduce the costs of offshore carbon storage sites. In such a facility, methane is degassed from produced brine, this brine is then cooled allowing the extraction of heat and then CO2 is dissolved into it for reinjection into a porous rock formation. Once injected into the porous reservoir formation, this CO2-loaded brine will sink due to its relatively higher density, providing secure storage. Here, for the first time, we investigate, the economic feasibility and energy balance of such a system within the UK North Sea. We examine the suitability of a depleted hydrocarbon field coupled with a saline formation located in the Inner Moray Firth, Scotland. We find that such a system would be highly likely to have a positive energy balance, and would be an order of magnitude cheaper that decommissioning. Furthermore, as only 10% of the sites storage capacity is needed for disposal of the CO2 emissions associated with its operation, there is significant potential for additional revenue creation from storing CO2 from other sources. Whilst the chosen case study site was not ideal, due to its relatively shallow depth, and hence lower that ideal heat potential, it demonstrates that reuse of redundant oil & gas infrastructure that would otherwise be decommissioned could help to offset some of the financial barriers to developing a carbon storage industry in the UK North Sea.