Heat extraction analysis of an innovative single-well open-loop geothermal system using scCO2

With the rising global energy demand and concerns about climate change, geothermal energy development has gained significant attention. Traditional enhanced geothermal systems face numerous challenges, prompting interest in single-well geothermal energy extraction systems due to their cost-effectiveness. This study innovatively proposes a supercritical CO2 single-well open-loop geothermal system (OLGS), which is the first to combine scCO2 with a single-well open-loop structure. A coupled flow and heat transfer model for the wellbore and reservoir is developed. The findings indicate that, compared with traditional working fluid (i.e., water), using CO2 as the working fluid can offer benefits such as forming a thermosiphon effect in the initial stage of heat extraction, with low pump-power consumption and stable thermal output over extended periods. The system performance is influenced by different flow modes: the backward flow can maintain a relatively high and stable production temperature over 20 years, while the forward flow is more advantageous in terms of thermal power. For injection parameters, a backward flow of CO2 at a mass flow rate of approximately 12.5 kg/s optimizes heat extraction. On the premise of meeting the outlet temperature requirements, minimizing the injection pressure is crucial for obtaining a higher thermal power, while the injection temperature has a minor effect on heat extraction capacity. This research provides a new approach for the design and optimization of OLGS, especially for the transformation of abandoned wells and the utilization of medium-deep geothermal energy.