Economic Analysis of CO2 Thermosiphon

Abstract

The use of CO2 to extract heat from engineered geothermal systems (EGS) is of interest due to the possibility of generating power at a lower cost than when using water. This lower cost would arise from its ease of flow through the geothermal reservoir, strong innate buoyancy which permits the use of a thermosiphon rather than a pumped system, and lower dissolution of substances that lead to fouling. Here we develop a costing/pricing methodology as a step towards estimating the economic potential of using CO2 as a heat extraction fluid instead of water. This costing methodology is applied here to a base case to give a general estimation of the price range for a CO2-based EGS. The impact on economics of changes in injection temperature, wellbore size, and recompression systems are addressed, and found to be significant. In general, the CO2-based system is found to be very sensitive to both assumptions in the pricing model (particularly well costs), and to process operational parameters. This work provides a starting point for optimisation of CO2-based EGS for economic performance.