Effects of lateral-well geometries on multilateral-well EGS performance based on a thermal-hydraulic-mechanical coupling model

Our previous study (Song et al., 2018) presented a novel enhanced geothermal system (EGS) with multilateral wells to exploit geothermal energy, and illustrated that the multilateral-well EGS had a better heat extraction performance than conventional double-well EGS. However, to further improve the heat extraction performance of the multilateral-well EGS, the effects of lateral-well geometries on multilateral-well performance should be studied and the geometrical parameters should be optimized. In this paper, we use a thermal-hydraulic-mechanical (THM) coupling model with a complex discrete fracture network (DFN) to investigate the influences of lateral-well geometrical parameters on the multilateral-well EGS performance. The lateral-well geometrical parameters include the lateral-well length, number, spacing and diameter. The results indicate that the longer lateral well and larger well spacing are beneficial for enhancing the multilateral-well EGS performance. In terms of better heat extraction performance and lower pressure impedance, the 400m well spacing is the optimizing value under the fracture density of 0.067 m(-1). The lateral-well number has a complicated effect on the heat extraction process. A large number of lateral wells can improve swept volume and reduce pressure impedance, but simultaneously connect more fractures and accelerate thermal breakthrough. Therefore, the lateral-well number should be optimized according to the specific DFN and under the DFN in this paper, 6 lateral wells are the best for the multilateral-well EGS performance. When there is a rotation angle between injection and production lateral wells, it can postpone the thermal breakthrough and be beneficial for heat extraction. The influence of the lateral-well diameter on the EGS performance can be ignored. The results of this study provide good guidance for the lateral-well design of the multilateral-well EGS.

Automated summary

The study shows that optimizing the geometrical parameters of lateral wells, such as length, spacing, and number, is crucial for enhancing the performance of multilateral-well EGS. Longer lateral wells and larger well spacing are beneficial for improving the EGS performance, while the number of wells should be optimized based on the specific discrete fracture network. The research provides valuable guidance for the design of lateral wells in multilateral-well EGS.