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.

Acknowledgments

We gratefully acknowledge the support of the Institut de l’énergie Trottier, Canada Foundation for innovation, the Government of Québec, CanmetEnergy, Belimo, Bouthillette Parizeau, Trane Canada, Mécanicaction, and Eautec for their support during the development, construction and operation of the geothermal mobile laboratory used during this research. We also thank the anonymous reviewers for their valuable suggestions, Léo Cerclet for the carrying out of the thermal needle probe tests, and Étienne Bélanger and Pierre Beaudry for their technical support.