CO2 flow in supercritical geothermal systems

Technological advances have allowed to target geothermal systems at greater depth and higher temperature in the supercritical regime. Supercritical geothermal systems (SCGS) could potentially provide a drastic increase in power generation, with estimates up to 50 MW per well. A handful of wellbores worldwide have either (or have shown potential to) reached supercritical resources in magmatic provinces. As a common occurrence in volcanic area, the resident fluid is not pure and mixtures of water and CO₂ are the norm. In this contribution, we will explore the flow conditions of H₂O-CO₂ mixtures at temperature and pressure conditions above the critical point of water. The multi-phase and multi-component problem of H₂O-CO₂ mixture flow is a non-trivial problem and few studies have been done in the past. We present finite element simulations with the open-source multi-physics framework MOOSE that explore the flow conditions of H₂O-CO₂ mixtures at high temperature and pressure. As a benchmark problem, we assume an injection of cold CO₂ into a water filled reservoir. We analyse the pressure and temperature changes and the evolution of the injected CO₂ in time. We show how gravity forces play a role in the long term and at relatively large distance from the injection. We discuss the potential of employing CO₂ as a working fluid in SCGS.