The Impact of an Open Loop Geothermal System with Multiple Wells on Groundwater Temperature

Abstract:

As the demand of groundwater as a source of energy has increased in recent years, the Upper Carbonate Aquifer beneath the City of Winnipeg is heavily utilized for cooling and heating. Majority open loop systems discharge thermal wastewater into the aquifer and increase the groundwater temperature. A numerical model was developed to study the impact of a geothermal system with multiple wells located in the Tuxedo area on groundwater temperature. Analysis was performed using SEAWAT with GUI Visual MODFLOW. Surface elevation, model boundary and wells locations were developed using ArcGIS. The model was run in steady state flow for static water level calibration and in transient mode for calibration using data of a pumping test. Preliminary investigation with three years simulation predicts a 600 m by 660 m area of temperature increase. Groundwater temperature in production wells will increase 0.5°C within 2 years and 1°C within 3 years. Factors that influence the temperature changes and its distribution in the groundwater are production flow rate, recharge flow rate, groundwater flow, return water distribution into recharge wells, distance between production wells and recharge wells, spacing between recharge wells, and layout of geothermal pumping wells. The simulated and observed temperature increase is mainly caused by higher production rate for cooling than for heating. The result from this study will strongly contribute knowledge in the development of a 3D numerical model of the Upper Carbonate Aquifer beneath the City of Winnipeg to investigate the impact of geothermal systems to the groundwater temperature.