The impact of rock fracturing and pump intake location on the thermal recovery of a standing column well: model development, experimental validation, and numerical analysis

Abstract

Significant energy savings can be generated by standing column wells. Despite a growing interest in these ground heat exchangers, very few simulation models have been validated against reliable field data. This article presents an extensive field program performed using a large-scale geothermal laboratory connected to a standing column well. The collected data are then used as direct input for the development and experimental validation of a finite-element model coupling heat transfer and groundwater flow. Simulations reproducing the conditions of a 6-day pumping test, a 24-day thermal response test, and a 25-day dynamic winter operation show that the model reproduces the drawdown at the well and the operating temperatures in both stable and dynamic conditions with a mean absolute error of 7.3 cm, 0.15 °C, and 0.32 °C, respectively. Further exploitation of the model suggests that near-surface fracturing can be detrimental to heat pump operation during winter-long heat extraction in cold climates, as it eventually favors recharge of the well with colder water. Lastly, it is shown that a top-pumped arrangement allows reducing costs and logistical problems associated with installation and maintenance of standing column wells with minimal impact on heat pump operation.