Design and optimization of deep coaxial borehole heat exchangers for cold sedimentary basins

Heating performance of deep borehole heat exchangers (DBHEs) is heavily impacted by its design and operating flow rate. Here, various designs of coaxial DBHEs were numerically simulated and compared for 1 year of continuous operation in a cold sedimentary basin using the FEFLOW software. Factors affecting performance, including: (1) depth, (2) repurposing an oil and gas (O&G) well or drilling a larger one, (3) repurposing options, (4) inner pipe material, made of either vacuum insulated tubing (VIT) or high-density polyethylene and (5) grout with different thermal conductivity were evaluated. Where an O&G well is available, the most cost-efficient option is repurposing, with the best performance obtained from the deepest and largest diameter wells. While VIT inner pipes performed better in some designs, their performance did not compensate for their cost.