Coupling Simulation of Seepage and Temperature Characteristic of Single-well Cycling Geothermal Collection System

Abstract

Single-well cycling geothermal collection technology collects shallow thermal energy through the circulating flow of groundwater in a closed single well, which does not consume or pollute groundwater. The technology has been promoted and applied for more than 20 years, and the application building area exceeds 20 million square meters. In order to further study the operation characteristics of this technology, the influence of system operation on groundwater seepage and temperature field is explored by combining theoretical research and numerical simulation. Firstly, a mathematical model of single-well cycling geothermal collection technology is established, and the theoretical solution of groundwater drawdown is derived, which is applied in practical engineering. Secondly, a three-dimensional water-thermal coupling numerical model is established to simulate the effects of changing pumping flow rate, aquifer permeability coefficient and operation mode on the distribution of seepage and temperature field. The results show that when the pumping flow increases by 50%, the waterhead at the injection section increases by 5m, while the pumping temperature changes by only 0.3 ºC. The permeability coefficient of aquifer affects the flow of circulating water underground, the injection water is blocked to flow to pumping zone when the permeability of aquifer in clapboard section is poor, which significantly reduces the fluctuation of pumping temperature, and a stable heat transfer temperature difference will be maintained.