Numerical modeling of a potential CO2-supplied enhanced geothermal system (CO2-EGS) in the Asgard field, Norway

Abstract

The principle of Enhanced Geothermal System (EGS) technology is that water injected at a sufficiently high pressure will lead to the fracturing of naturally impermeable rocks, and as a result, this will create hydraulic communication between wells. In this way, reservoirs not previously considered to be perspective can provide geothermal heat to the surface. Since nearly two decades, $CO_{2}$ is considered, mostly theoretically, as a working fluid that can potentially provide higher net power output than water in EGS’s installation. In this respect, the possibility of accessing high-temperature heat from the Are and Tilje formations located on the shelf of the Norwegian Sea was analysed. The estimated temperature at the reservoir depth of 4,500–5,000 m is not less than 165°C. For this, a 3D numerical modelling was performed in order to analyse 10 different scenarios for heat extraction using supercritical $CO_{2}$ ($sCO_{2}$) as a working fluid. Results indicate that appropriate matching of the mass flow and temperature of the injected $CO_{2}$ allows to avoid premature temperature decline in the reservoir. However, as Are and Tilje formations are built from highly porous and relatively highly permeable rocks, the fluid entering the production well will always be a mixture of $CO_{2}$ and water. This is advantageous from the point of view that a significant part of the injected $CO_{2}$ is trapped in the reservoir, while the higher water content in the production well allows a significant temperature drop during fluid extraction to the surface to be avoided.