CO2-Dissolved: successfully combining CO2 storage and geothermal heat extraction
Design for a storagefacility for dissolved CO2 in a saline aquifer combined with geothermal heat production.
While there is no doubt that geological storage of CO2 is necessary to cut atmospheric greenhouse gas emissions, the implementation,safety and monitoring conditions required raise scientific, technical, economic and social issues that are slowing its development in the short term. Storing CO2 on a small scale close to the emission sources would be an additional and possibly alternative solution. The 3-year ANR CO2Dissolved project explored this possibility. With 7 partners* co-ordinated by the BRGM, the project demonstrated the feasibility of combining the storage of dissolved CO2 in an aquifer with the extraction of geothermal heat.
This solution has several advantages. The idea is to store the CO2 produced by an industrial facility on the same site by injecting it in dissolved form into an underlying deep saline aquifer. The water is pumped up and subsequently reinjected with the dissolved CO2 through one "injection" and one "production" well, similar to the geothermal doublets used to supply heating networks. In situ CO2 storage would reduce both the costs and risks of transporting the gas, which, in addition to heat recovery, makes this an attractive solution, subject to the existence of suitable aquifers in the right location and proper control of the process.
The experimental MIRAGES-2 set-up for injecting a mixture of water and dissolved CO2 into a core under pressure and temperature conditions typical of a deep aquifer.
Feasibility and risk control
Because CO2 is only is soluble in brine within certain limits, and because of the standard flow rates in geothermal doublets (250-350 m3/h in the Paris Basin), this is a relevant solution for small-scale industrial emissions of CO2 (< 150 000 t/year). The storage sites targeted are deep aquifers (1 500 - 2 500 m) with temperatures in the region of 60 to 80°C. In France, 650 potentially compatible industrial sites (accounting for 25% of emissions in France) have been identified.
The American partners of the project have developed an innovative CO2 capturing process in which water is the only solvent. Possibilities for integrating this process into the CO2Dissolved system have been investigated, and depend on CO2 concentrations in flue gases and the possible need for separation prior to injection. Unlike large-scale storage, where the CO2 is injected in supercritical form, in this case it is entirely dissolved in the brine of the aquifer. This removes the risks of a gas bubble forming underground, which could rise to the surface.
The impacts on the rock of injecting acid water and the resulting chemical reactions that depend on the hydrogeological characteristics of the environment have been digitally simulated and repeatedly tested at an experimental facility. The economic impact has also been investigated, in the case of a sugar mill and distillery in central France, and has demonstrated the viability of most of the scenarios simulated, thanks to the economic benefits of the heat recovered.
The next stage will be to implement a demonstration pilot on an industrial site. The first steps are already under way with the new "Pilot CO2-Dissolved" project financed by the Géodénergies scientific interest group.
3D tomography of induced porosity (in blue) 20 days after injecting acidified water (through the vertical tube) into an initially cylindrical and highly homogeneous limestone core.
- BRGM (France, coordinateur)
- BGR (Allemagne)
- CFG Services (France)
- Geogreen (France)
- GeoRessources (France)
- LEO (France)
- Partnering in Innovation, Inc. (USA).