Evaluation of the multi-doublet performance in sandstone reservoirs using thermal-hydraulic modeling and economic analysis

A good understanding of the long-term multi-doublet performance is imperative to sustainable and economical hydrothermal production with reinjection in sandstone reservoirs. This paper presents a case study from the Guanzhong Basin, northwest China to systemically evaluate the performance of different multi-doublet layout plans in two sandstone reservoirs through 3D thermal-hydraulic modeling and economic analysis. Based on the single-doublet models designed to determine the optimal well spacing to improve heat extraction performance, the multi-doublet models are established for five multi-doublet layout plans with different well spacing at 500, 600, and 700 m and flow rate at 125 and 200 m³ h⁻¹, respectively. Results indicate that the different layouts and doublet orientations with respect to the natural groundwater flow can lead to a difference of about 25% in energy production and 15% in the Levelized Cost of Heat (LCOH) for an assumed lifespan of 50 years. The well spacing and flow rate have a great impact on the determination of the optimal multi-doublet layout. The change in well spacing can lead to a difference up to 35% in energy production and 25% in LCOH, and the change in flow rate can lead to a difference up to 54% in energy production and 40% in LCOH. Compared with checkboard configurations, better doublet performance is achieved in tramline configurations due to a strong cross flow occurs among doublets. Moreover, the reservoir with greater permeability has higher recovery efficiency and prominent superiority of tramline configurations. Results offer decision-making support to the geothermal development in the areas where 100% fluid reinjection is mandated for environmental and resource conservation.