Production performance of a novel open loop geothermal system in a horizontal well

A novel open-loop geothermal system (OLGS) in a horizontal well is proposed to achieve efficient and large-scale development of hydrothermal resources. Compared with the vertical-well extracting groundwater system, drilling and completion costs can be significantly reduced by accomplishing fluid injection and production in one horizontal well. The horizontal-well OLGS showed improved performance and can have broader application prospects than the vertical-well extracting groundwater system and conventional vertical-well OLGS, particularly in not-so-thick reservoirs. Therefore, the horizontal-well OLGS is expected to be useful in accelerating the exploitation of hydrothermal resources. Although some OLGS studies have been reported, no comprehensive parameter analysis of the OLGS has been performed until now, which hinders its application. In this study, a 3D unsteady-state model based on local thermal non-equilibrium is established and validated using an analytical model. Results show that variations in the pressure and flow behaviour generally occur within 50 m near the wellbore, whereas the maximum impact scope of the cooling region is 85 m, serving as the critical value for the fracturing operation region and well-spacing design. The influence of dominant engineering and reservoir parameters on the production temperature, heat output, fluid injection, and production were investigated. Sensitivity evaluation was performed to compare the effects of various parameters. Furthermore, the performances of OLGS with horizontal and vertical wells were compared for the first time, indicating that the horizontal-well OLGS can achieve improved performance via a long horizontal well. The results can offer guidance for application designs of the horizontal-well OLGS and traditional vertical-well OLGS. Furthermore, they can promote the rapid development of horizontal-well technology for the exploitation of geothermal resources.