With so many carbon emission sources that could be mitigated, it is important to identify all potential subsurface storage locations. Deep saline aquifers are widely distributed and have been successfully used for many years. With carbon based power generation likely for several more decades, this is a technically proven solution to eliminate harmful emissions. Intermittent renewables are being scaled up, but coal usage has unfortunately increased in US, Europe, and other locations due to climate related intermittency. CCS is ready to capture and store these emissions. Economics are based on avoiding carbon taxes, cross-border carbon duties for exports, and to meet regulatory requirements.
- Carbon dioxide emissions from carbon based fuels and processes are well understood. Waste and biomass combustion for power also produces CO2 and CCS is technically feasible in these scenarios as well. There are multiple CO2 emission sites able to be considered for CCS;
- Previously we discussed using depleted oil & gas reservoirs for storage, but CO2 has also been successfully stored in deep saline aquifers. These aquifers are attractive due to much wider geographical distribution, and often may be located closer to CO2 emission sources;
- Some of these aquifers are in the same stratigraphic unit as known oil & gas reservoirs (e.g., In Salah), some are more shallow and located above known oil & gas reservoirs (e.g., Utsira Formation, Sleipner), some are deeper (e.g., Tubåsen Formation, Snøhvit), but many are located away from oil & gas areas (e.g., naturally fractured carbonate reservoir Tyrrhenian Sea @ right);
- Storage of supercritical CO2 into these aquifers would use conventional wells and surface facilities. Reservoir modelling is used to ensure storage integrity including sealing capacity, pressures, and geomechanical effects (i.e. dilation of incipient fractures or microseismicity);
- CO2 sequestration is usually through stratigraphic and structural trapping with some residual and solubility trapping. Certain types of aquifer rock lithologies may facilitate another form of sequestration involving geochemical reaction with rock minerals (sandstone and feldspar);
- Some of these aquifers may be candidates for geothermal developments and/or extraction of minerals (e.g., lithium) from brine, so in these cases there may be attractive synergy with CCS development systems;
- As the use of emission free Renewable Energy sources are scaled up, it is inevitable that conventional carbon based fuels will continue to be used globally for another couple of decades, but CCS offers a way to mitigate these emissions safely and effectively. Economics would be based on avoiding carbon taxes and cross-border duties and satisfying regulatory requirements.