The sustainability of geothermal energy in an aquifer
A mathematical model
M.R. Jellema (TU Delft - Electrical Engineering, Mathematics and Computer Science)
BJ Meulenbroek – Mentor (TU Delft - Mathematical Physics)
B. Bera – Mentor (TU Delft - ChemE/Transport Phenomena)
C. R. Kleijn – Graduation committee member (TU Delft - ChemE/Transport Phenomena)
J.H. Weber – Graduation committee member (TU Delft - Discrete Mathematics and Optimization)
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Abstract
Geothermal energy plays a role in advancing clean energy solutions for a sustainable future, which is why we investigate the sustainability of geothermal systems in an aquifer. The geothermal system examined in this research operates using two wells, positioned 1 km apart. One well pumps cold water into the porous medium and the second well pumps warm water out of the aquifer. As warm water is extracted, the temperature of the aquifer decreases. This cooling disturbs the chemical balance of the minerals in the water, which can lead to precipitation reactions. This precipitation reduces the porosity and consequently the permeability of the aquifer. The temperature distribution is modeled using the pressure and velocity field. This showed that the aquifer had cooled to 40˝C in 6 years. According to this result, the use of a geothermal aquifer is not sustainable. The cooling within 6 years is not accurate, because the boundary conditions that were selected were not fully chosen to reflect the complexities of the system and we didn’t properly consider the heat coming from Earth’s core. Precipitation reactions lead to an increase or decrease in concentration of various minerals in the water. These reactions cause deposits of solid minerals on the grains or porous rock, causing the aquifer to clog, allowing less and less water to flow through. In this model, the amount of precipitation was very small and therefore had little effect on the water flow and the sustainability of the aquifer.