Globally scalable geothermal energy production through managed pressure operation control of deep closed-loop well systems

Highlights: • A deep closed-loop geothermal well concept is proposed for scalable power generation. • The proposed concept does not rely on flow through fractures and rock permeability. • The concept can be applied globally using available directional drilling technology. • An automated managed pressure operation system ensures real-time wellbore stability. • Transient hydraulic modeling shows initial thermal power generation of above 25 MW. Closed-loop geothermal systems (CLGS) have been recently proposed as an alternative to the conventional enhanced geothermal system (EGS) concept to address many of the issues of concern with EGS, such as potential contamination of the circulating fluid and short-circuiting. Deep CLGS wells drilled in rock formations with in-situ temperatures above 200 °C could in theory be drilled anywhere around the world, thereby allowing for globally scalable geothermal energy production. A novel concept of integrating a managed pressure operation (MPO) system with deep CLGS (DCLGS) is presented here. The concept includes an open-hole completion of the lateral section, while the automatically controlled MPO system maintains wellbore integrity and avoids fluid contamination. A combined thermal and hydraulic model is also developed to demonstrate the feasibility of this concept. Using a robust semi-implicit numerical algorithm, the model can simulate the fast transients in a well, which enables the application of automated MPO control for real-time control of a DCLGS. Simulation results show that a 7 km deep U-shaped well with a 7 km open-hole lateral with a reservoir temperature of 250 °C can generate a thermal power of around 28 MW initially when the pump rate is set to 350 m³/h. The results also show that casing of the lateral section has little impact on the outlet temperatures and thermal powers. An optimally insulated return section can increase the output power by 2%. The effect of pump rate is also studied. Even though the outlet temperature decreases, increasing the pump rate can improve the thermal power by 15%, when the pump rate is increased from 250 to 450 m³/h.