Periodic Reporting for period 1 - CO2SINk (Carbon dioxide (CO2) Storage In deep volcaNic areas)
Reporting period: 2023-06-01 to 2024-11-30
We need to become a carbon-neutral society as soon as possible to minimize the effects of climate change. This necessity implies urgent action to a complex problem that requires multiple solutions. Among the available solutions, Carbon Capture and Storage (CCS) is considered as a key technology to reach zero emissions because not only will it contribute to reduce CO2 emissions of the energy sector, but also will permit eliminating emissions in the hard-to-abate industry. The hard-to-abate industry represent some 10% of the total CO2 emissions, i.e. 4 Gt/yr. Therefore, we have to rely on CCS at the gigatonne scale to reach net-zero emissions. Thus, we need as much CO2 storage capacity as possible while reducing the main risks of CCS, i.e. CO2 leakage and induced seismicity. In conventional CO2 storage in deep sedimentary formations, CO2 is lighter than water and, thus, the risk of CO2 leakage is an issue. Alternative storage concepts have been proposed to reduce the CO2 leakage risk: (i) achieving a fast fixation of carbon through mineralization and (ii) injecting CO2 already dissolved into the brine. In both cases, the injection rates should be low because CO2 dissolution into brine is around 4%, so the amount of injected CO2 is 25 times smaller than that of CO2 if injected in free phase. To circumvent this issue, CO2SINk proposes a novel CO2 storage concept in deep volcanic areas where water stays in supercritical state, i.e. pressure>22.1 MPa and temperature>374 ºC, because at these conditions CO2 becomes denser than water and, therefore, sinks. This concept not only reduces the leakage risk, but also permits injecting large amounts of CO2, which is necessary to effectively reduce CO2 emissions to mitigate climate change. This novel storage concept would benefit society by (1) enhancing the CO2 storage options and (2) reducing the risk of CO2 leakage. CO2SINk is in line with the European Green Deal – the EU´s roadmap in transforming to a sustainable economy and industry –, which sets clean and secure energy supply and CCS among the priorities. These priorities are also dealt with the 7th and 13th UN Sustainable Development Goals targeting “affordable and clean energy” and “climate action”, respectively. The overall objective of this Proof of Concept is to explore the commercialization possibilities of this novel concept of geological CO2 storage.
The first task was to simulate in 3D the evolution of groundwater movement induced by the presence of a high-temperature magmatic chamber. Groundwater heats up and lighter when it gets in contact with the magmatic chamber, forming a rising convective cell. Previous numerical calculations of the shape of the convective cell to estimate the location of supercritical resources had been made in 2D plane-strain geometries. In CO2SINk, we have performed pioneering 3D numerical simulations of the effect of the presence of a high-temperature magmatic chamber on the hydrothermal development of a convective cell. We have found unexpected results, with the shape of the convective cell significantly differing from that resulting in 2D simulations. Our findings show a convective cell that grows above the perimeter of the magmatic chamber, but that sinks above its central part. This finding has important implications for deciding the best location of the wells to reach supercritical water. Drilling above the centre of the magmatic chamber may result in unsuccessful wells not reaching supercritical conditions of water. In contrast, wells drilled around the projection of the perimeter of the magmatic intrusion have higher chances of finding supercritical water. This finding has implications not only for the CO2 storage concept proposed in CO2SINk, but also for harnessing supercritical water in deep volcanic areas. We have investigated the effect of the shape and depth of the magmatic chamber on the distribution of supercritical water and its evolution over geological time scales. With the discovered shape of the convective cell that is formed above magmatic intrusions, we have performed simulations of CO2 injection within the region where supercritical water is present. Simulation results display a moderate sinking tendency, with the CO2 plume evolving quasi-spherically around the injection well. The other potential risk that has been investigated is the potential of inducing seismicity. We observe a dependency of the induced seismicity rate on the pressure evolution, but a limited effect of long-term cooling in our simulations, which involve injection rates of 1- to 5-million tons per year during 40 years. Nonetheless, we do not disregard that cooling-induced seismicity may become an issue for multi-well injection of cold CO2 over decades. Site-specific studies should be performed to assess the injection rates that do not lead to long-term cooling-induced seismicity.
Deep volcanic areas have received limited attention because when operators drilled deeper in hydrothermal systems in the search for higher temperatures, they did not find a significant temperature increase with depth. However, the interest in deep volcanic areas has been revived because it has been numerically shown that temperature rises again with depth below a certain depth and supercritical water could be found. Reaching supercritical water is of paramount importance to decarbonize the energy sector, because the power generation per well would be one order of magnitude higher than in a conventional hydrothermal well because of the high enthalpy and high compressibility of supercritical water. We have discovered that in addition to generate large amounts of reliable clean energy, supercritical reservoirs can provide a safe way of storing large amounts of CO2 because at the pressure and temperature conditions of supercritical systems, i.e. pressure>22.1 MPa and temperature>374 ºC, CO2 becomes denser than water and, therefore, sinks, significantly reducing the CO2 leakage risk. Supercritical conditions of water have been reached in a few wells all around the well, but it has not been possible to maintain fluid circulation for long. Identification of supercritical reservoirs is still challenging and has been attempted by trial and error. Each well trying to reach supercritical water costs several millions of euros, so delimiting the most likely zones where supercritical water could be found is paramount. The findings of CO2SINk have advanced the state of the art by showing that supercritical water is likely to be found above the perimeter of magmatic chambers, rather than above their centre, as previously thought. This finding should be supported by future drilling projects, like the Icelandic Deep Drilling Project (IDDP). Further technological developments are also needed to test in the field the CO2SINk concept of storing CO2 in supercritical reservoirs because wells reaching supercritical water have, to date, suffered from clogging and/or corrosion and had to be abandoned prematurely. As the technology advances and further developments towards harnessing geothermal energy from supercritical water are made, the novel CO2 storage concept proposed in CO2SINk could be tested under relevant conditions and eventually be deployed to significantly reduce CO2 emissions and contribute to reach carbon neutrality.