Energy analysis for guiding the design of well systems of deep Enhanced Geothermal Systems


The focal objective of this work is to calculate the energy consumption for constructing the EGS (Enhanced Geothermal Systems) wells, to examine the energy (heat and power) performance of such well systems, and to propose and evaluate several ways for improving that performance. A model was developed to compute the pressure and temperature fields of the geofluid flowing in the production and injection wells to be able to calculate the flow pumping energy consumption, and the heat gain/loss during its flow in/out of the enhanced reservoir, for wells up to 10 km deep. The total well construction energy consumption was calculated to be 19.40 TJ/(km of well) for the considered well configurations, and increases approximately linearly with the flow cross section area of the well. Several ways to improve the energy performance of the wells, by increasing the heat output of the production wells and decreasing the required power for pumping the geofluid were evaluated: (1) increasing the number of injection/production wells to reduce the pressure drop in each, (2) increasing the flow cross section of the injection/projection well, and (3) adding thermal insulation to the circumference of the production wells (to reduce the geofluid heat loss to the rock). Most of these methods were found to indeed increase the power output of the geothermal system but have increased the construction energy requirement somewhat more. More energy efficient drilling methods and materials of lower embodied energy can lead to a higher EROI (energy return on investment). The EROI of the recommended EGS well system designs ranged from 33.8 to 286.2.