This paper presents the concept of harnessing geothermal energy from heavy oil fields that have undergone steam-flooding and so accumulated substantial heat from steam injection. Once the steam-flooding process reaches economic cut-off, due to high water cut and/or high steam-to-oil ratio, the reservoir would be abandoned, leaving behind stored energy in the form of heat. From this point, the reservoir could be regarded as an artificial geothermal system, and its intrinsic heat recovered by water circulation. A compositional, thermal simulator was used to model the overall heat transfer efficiency throughout the reservoir. The Fourth SPE Comparative Solution Project (problem 3) - complemented by parameters obtained from well-known analogue fields - was adopted to build the base case scenario. Sensitivity analyses were then performed to identify critical parameters that may affect the potential for harnessing the geothermal energy. The reservoir simulations were then coupled with semi-analytical computational of the heat exchange between wellbore and surrounding formation to estimate the total surface heat recovery. The latter could be used for either direct heating or electricity generation, depending on the arrival fluid temperature. State-of-art technology for converting heat from low-enthalpy resources ("waste energy") into electricity were evaluated, together with an estimate of the parasitic load associated with ancillary facilities necessary to run operations beyond the oil-recovery phase. This study shows that it could be possible to advantageously extend the life of heavy oil fields by means of a heat-recovery phase after the oil-recovery phase.