Impact of Formation Thermophysical Properties on Geothermal Energy Potential Assessment

Geothermal exploitation has high upfront costs and long return-on-investment periods. Without evaluating geothermal potentials accurately, it will be high risky to proceed with these projects. Formation thermophysical properties including thermal conductivity, specific heat capacity, density and dynamic viscosity are critical parameters in geothermal resource assessment and modeling. Despite the importance, very few studies have explored their combined effect and sensitivity analysis. This paper investigates how these properties affect geothermal potential evaluation, thus identifying key parameters and the need of obtaining them accurately from well logs or laboratory measurements. Wellbore heat transfer is the fundamental process that affects significantly the assessment of production potential of geothermal energy from a well. A wellbore model is established to simulate thermal flow dynamics and heat transfer processes around the wellbore. The model enables to investigate the effect of formation thermophysical properties on fluid temperature and thermal energy produced at the wellhead. Thermophysical properties of the formation and fluid play different roles in the determination of output fluid temperature and geothermal energy. Fluid specific heat capacity and density are the most important parameters affecting the assessment of production potential of thermal energy from a geothermal well, while the role of fluid thermal conductivity is negligible. Formation thermal conductivity is also a critical factor in predicting the heat loss to the surrounding formation. A low formation thermal conductivity can reduce heat loss and increase energy production. Compared to other properties, formation density and specific heat capacity have a negligible effect on the evaluation of production potential of a geothermal well. Fluid specific heat capacity exhibits strong salinity and temperature dependence: it decreases as salinity increases, and increases as temperature increases.