| Title | Utilisation and Sequestration of Supercritical Carbon Dioxide in the Geothermal Field |
|---|---|
| Authors | T. Tosha and T. Ozaki |
| Year | 2020 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Hot Dry Rock, Global warming, CO2, Sequestration, Utilisation |
| Abstract | Geothermal energy is expected as one of the renewable energies against the global warning, which we have to overcome in this century. However, the conventional geothermal development that pumps up and uses the subsurface hot water has not been much promoted because of the objection of the local residents. The Hot Dry Rock (HDR) method, which does not pump up underground hot water, was studied but suspended by economical and other reasons. The HDR technology creates an artificial reservoir by hydraulic fracturing at the area where natural geothermal system is not or poorly developed, and pressurises water into the reservoir to extract subsurface heat. Several demerits have been pointed out such as the outflow of water from the reservoir, and the low temperature due to the bypass of injected water (Short Circuit). The induced earthquake during the hydraulic fracturing and the water circulation is another matter of concern. Carbon dioxide (CO2) in the supercritical condition (ScCO2) has better thermal properties as the heat transport fluid than water. ScCO2 inhibits the dissolution from host rocks and the sedimentation of minerals in the fractures. Large buoyancy can be expected to reduce the pumping energy. Also, ScCO2 can penetrate into narrow micro-cracks due to its small viscosity. An output of about 1.5 times that of water can be expected with use of ScCO2 as a working fluid. ScCO2 that migrates from the flow path would be expected to be sequestered and fixed as carbonate minerals in HDR. In addition, the formation of the Short Circuit and the scale production might be overcome by controlling CO2. The induced earthquakes at the reservoir creation can be also suppressed by using CO2 as a fracturing fluid. There are many advantages in use of CO2 but are also many subjects to be solved. We will progress a new geothermal research program using CO2. In this paper, subjects on the use of CO2 in the geothermal field and the processes to the implementation will be discussed. |