Geothermal energy has received global attention for being a clean, sustainable and cheap energy source. Numerical modeling is currently an integral part of all the stages of geothermal processes such as exploration and development. In this 3D simulation study, a low-temperature geothermal doublet has been considered. In such system, hot water is produced from one well (producer) and cooled water whose heat content has been depleted by a surface heat exchanger is re-injected underground through another well (injector). This work tests the practicality of employing the Finite-Volume based Dumux simulator for modeling the development of the cooled-water thermal front over the years.