Cost optimization of borehole heat exchangers based on saturated geophysical exploration

As the core component of closed-loop ground-coupled heat pump (GCHP) system, the construction quality and cost of borehole heat exchangers (BHEs) directly determine the investment effectiveness and system operational stability. Carbonate rock areas are characterized by complex geological conditions, where drilling operations are highly susceptible to borehole collapse, leading to a persistently high re-drill rate. Consequently, the investment of the ground-source side accounts for approximately 60% of the total construction cost, forming a major bottleneck for the large-scale development of shallow geothermal energy. This study first analyzes the BHE cost composition and key influencing factors, such as the re-drill rate and geological transparency. Subsequently, a saturated geophysical exploration scheme and a site geological transparency evaluation method are proposed. Based on the mathematical relationship among the re-drill rate, geophysical exploration cost, and additional construction costs, a selection model for geophysical scheme is constructed. Case studies using the control variable method are conducted to compare the economic efficiency of conventional and saturated geophysical exploration schemes under varying re-drill rates and project scales. The results indicate that at a constant total length, a higher re-drill rate magnifies the cost advantage of the saturated geophysical exploration scheme, saving up to 95.5% of additional costs. Furthermore, for projects with identical re-drill rates, projects with a larger scale achieve higher coverage rates per geophysical exploration line, yielding superior cost-saving effects.