Study on heat extraction performance of multiple-doublet system in Hot Sedimentary Aquifers: Case study from the Xianyang geothermal field, Northwest China

Abstract

Hot Sedimentary Aquifers (HSA) are often rich in geothermal resources that are particularly suitable for direct-use. Fully understanding the effect of well layout and primary geological /human-controlled parameters in a multiple-doublet system on the fluid flow and heat transfer processes is imperative to achieve efficient heat extraction in HSA. In this study, two multiple-doublet layouts, chosen by considering the natural groundwater flow direction, reinjection-well-led (R-led) scenario and production-well-led (P-led) scenario, are proposed. Their heat extraction performance in hot sedimentary reservoir models based on Xianyang geothermal field in the Guanzhong Basin, Northwest China is systematically investigated using the coupled thermal-hydraulic modeling and economic analysis. Results indicate that thermal breakthrough occurs earlier in the production zone when the reinjection induced artificial flow is in the same direction as the natural flow. Under the P-led scenario, which is superior to the R-led scenario in preventing premature thermal breakthrough and lowering the Levelized Cost of Heat (LCOH), the doublet lifetime and energy production are increased by up to 36% and 33%, respectively. The optimization of multiple-doublet layout can improve energy recovery in reservoirs with greater permeability. In the case of the minimal negative interference of the natural flow field and adjacent geothermal production, the energy production can be increased by up to 2.2 times. Furthermore, due to the integrated effects of the higher energy production and larger initial investment in the deeper reservoir, the LCOH and its dependence on well depth decrease with reservoir depth. Sensitivity analysis highlights that a 10% decrease in the drilling cost can lower the LCOH by 6.4% for the deepest reservoir. This study will contribute to the optimization of the design of multiple-doublet systems for efficient geothermal exploitation in HSA.