Transient thermal performance of U-loop geothermal systems with dual-borehole lateral sections using a computationally efficient framework

Advancements in directional drilling technologies have facilitated the development of advanced geothermal system configurations at greater subsurface depths. One example is the enhanced U-loop geothermal configuration demonstrated in a pilot field study in Alberta, Canada, featuring dual lateral boreholes in the horizontal section. This study develops a transient numerical model of a conjugate ground–wellbore system representing a U-loop geothermal configuration with dual lateral sections, incorporating the superposition principle to account for thermal interactions between the boreholes. The model is validated against 516 days of field data from the Alberta pilot demonstration, achieving a maximum error of 4.5% in predicting outlet water temperature. Two geothermal system designs are evaluated with installation depths of 2.4 km and 7 km, corresponding to bottomhole temperatures of 78 °C and 221 °C, respectively. The effect of single- and dual-lateral configurations is investigated, showing that the modified design extracts about 110% more thermal power on average. A thermal to electricity conversion analysis shows that the enhanced configuration delivers geothermal water at 155 °C to the power plant inlet, resulting in 57% greater electricity generation potential than the conventional U-loop configuration under the same operating conditions. A techno-economic analysis shows that, although the additional lateral borehole increases drilling costs by 14.5%, the levelized cost of energy is reduced by 28.5% compared to the conventional U-loop configuration. A series of parametric studies on operational conditions further demonstrates that extending casing insulation length can mitigate 2.9–7 °C/km temperature loss during upward circulation at low flow rates associated with longer fluid residence times. Overall, this study provides key insights into the long-term design, optimization, and techno-economic performance of enhanced U-loop geothermal systems for integrated electricity generation and direct-use heating applications.