Borehole Thermal Extraction Systems
July 14, 2010
One potential use of the coupled SVFlux™ and SVHeat™ Professional software packages is the analysis of geothermal systems. There has been recent focus on the performance of geothermal systems in the industry as an alternative energy source. One aspect of geothermal systems is pumping heat into large underground aquifers and then extracting that heat at a later time and/or a later position in the aquifer. This concept shows promise but for it to work properly there must be a mechanistic understanding of the processes involved. A 2D or 3D numerical model of such a system provides an excellent way to predict possible performance.
When heat is injected into the upstream area of the aquifer there is a buoyancy effect which takes place because of the hot liquid. Therefore the tendency of the heated water is to flow along with the groundwater as well as rise to the top surface of the aquifer. This tendency can be replicated in the numerical SVFlux™ and SVHeat™ coupled model. The coupled software solves for both convective and conductive heat flow. The software also implements injection and extraction wells for the estimation of water and heat flows for different rates and temperatures of injection. Summaries of total energy contained in the aquifer system can be produced over time. Heat flow in and out of the aquifer can also be reported as a function of time.
The following 2D and 3D examples illustrate the use of the SVFlux™ and SVHeat™ software packages to compute underground water and heat flow in a partially confined aquifer.
Figure 1 is the pattern of water injection and extraction changing with time. The water is injected and extracted at the same rate in the first 10 days of each month.
Figure 2 illustrates increasingly warm temperature while warm water is injected. The warm temperature is developed due to thermal conduction, thermal convection, and water density-dependent buoyancy. The rise of warm water and flowing down of cool water can be observed.
Figure 3 illustrated thermal energy balance and heat storage performance with time.
Figure 4 is the change of mean temperature of the injection wall and extraction well with time.
Figure 5 is identical to Figure 1, but applies to the 3D model.
3D model simulations are illustrated in figures from Figure 6 to Figure 9.
Figure 1: Pattern of Injected and extracted water
Figure 2: 2D Borehole heat injection and extraction
Figure 3: The change of injected, extracted, stored and lost thermal energy with time (Distance of Extraction well from injection well is 600 m)
Figure 4: The change of mean temperature with time for injection and extraction well (Distance of Extraction well from injection well is 600 m)
Figure 5: The pattern of water injection and extraction used in 3D model
Figure 6: 3D model of borehole injection and extraction system
Figure 7: Warm temperature development on XZ plane of 3D model of borehole injection and extraction system at the time of day 240
Figure 8: Warm temperature development on YZ-plane of 3D borehole injection and extraction system at the time of day 240
Figure 9: Warm temperature development on XY-plane of 3D model of borehole injection and extraction system at the time of day 240
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