A downhole heat exchanger for horizontal wells in low-enthalpy geopressured geothermal brine reservoirs

• A downhole coaxial heat exchanger (DHE) design inside deviated wellbores is proposed.
• Two flow path configurations are analyzed to maximize the heat extraction in the DHE.
• Several design and operating parameters are varied to select the DHE configuration W.
• DHE was coupled with an ORC power plant and a 3-D geothermal reservoir simulator.
• Field case study of south Louisiana reservoir showed 350 kW production over 30 years.

Geothermal energy is a clean, renewable energy resource that is widely available and reliable. Improved drilling and heat conversion systems make geothermal energy an increasingly attractive alternative. Downhole heat exchangers (DHEs) can accelerate the development of geothermal energy by reducing the capital cost and the risk of microquakes or subsidence. However, low-enthalpy geothermal resources are difficult to develop economically because of low heat extraction efficiency.In this study, a coaxial DHE concept is proposed to exploit forced convection driven by a downhole pump inside a horizontal wellbore. Two configurations of the proposed design are introduced, each having different flow paths for working and reservoir fluids. One system – which circulates working fluid through the inner-most tubing in the coaxial arrangement has better thermal exchange efficiency of about 29%, and is evaluated by coupling it to a simple model for a binary power generation plant and a geothermal reservoir simulator. Thermodynamic analysis evaluates the DHE performance for electricity generation. A field case study of the Camerina A reservoir (Vermillion Parish, Louisiana) demonstrates a net power of about 350 kW can be generated by a turbine even after 30 years of production.