Topside cycles for enhanced geothermal systems with CO₂ and hydrocarbons as working fluids

One concept for enhanced geothermal systems (EGS) described in recent literature is based on circulating CO₂ through a reservoir where the thermosiphon effect becomes strong enough to sustain strong self-circulation such that both pressure and temperature differences can be utilized for power production topside. The topside system operation influences the thermosiphon-driven fluid mass flow and the state at production well. The total system behaviour must therefore be considered to maximize net power output. In this work, a case study is defined based on conditions representing a location on the Norwegian continental shelf. A system model comprising direct and hybrid (with additional ORC) systems, and a simplified well and reservoir flow- and heat transfer model is developed. Two solutions for topside systems are evaluated with the aim of maximizing net power production. Both direct expansion of the CO₂ reservoir fluid, and a combination of direct expansion with an indirect ORC cycle are investigated.