Assessment of geothermal energy extracted from upper carbonate aquifer beneath the City of Winnipeg
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Date
2019-04-01
Authors
Susanto, Sylvia
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Abstract
The Upper Carbonate aquifer beneath the City of Winnipeg has been utilized as a heat source and sinks since the 1940s. The majority of open loop geothermal systems in Winnipeg extract groundwater from the Upper Carbonate aquifer, run the groundwater through a heat exchanger and return the thermal wastewater back into the aquifer. Injection of thermal wastewater creates thermal plume surrounding the injection well and thermal feedback which causing groundwater temperature increase in the production well. The first objective of this study was to provide information and resources on the current usage and impacts of the geothermal systems for engineers, scientists and the public in general. The analysis was carried out by developing maps, such as location and utilization of geothermal systems, the rate of groundwater being diverted, the quantity of groundwater diverted annually, the locations of production and recharge wells, the depths of casing and open hole for production wells, and the estimated heat balance. Assessment indicated up to 80% of the estimated heat was injected into the aquifer by extracting groundwater up to 100% of the permissible quantity. Analytical approaches were applied to estimate the thermal breakthrough time, the abstraction temperature, and thermal plume caused by heat injection. The results were in good agreement with recorded data and numerical analysis. Therefore, these approaches should be included in initial stage development of geothermal system to assess the sustainability of the system and the potential thermal interference in an urban area.
The second objective was to study the impact of an open loop geothermal system with multiple wells on groundwater temperature by developing a 3D numerical model of the Upper Carbonate aquifer in the southwestern part of Winnipeg. The model was developed using hydrogeological maps, provincial observation wells, geothermal system wells, and earlier research on the carbonate bedrock aquifer. Three steps of calibration were performed: constant hydraulic head, pumping test, and heat transport. Result indicated that extracting groundwater using all supply wells produced low entering water temperature. Long term simulation showed that higher groundwater flow increased thermal plume size, while high temperature created higher temperature zone within the thermal plume.
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Keywords
Groundwater, Geothermal Energy, Open loop geothermal system, Numerical model