Retrofitting depleted oil wells into geothermal wells can potentially solve the main issues in conventional geothermal wells: high capital costs for drilling geothermal wells and high risk of environmental consequences. For this application, the understanding of the temperature change is crucial as it affects the performance of the wellbore heat exchanger and the power generated from this well. Therefore, the current study is focused on the evaluation of oil wellbore's feasibility as a geothermal energy resource via investigating the heat transfer in the wellbore using computational fluid dynamic (CFD) approach based on actual measured thermal parameters of cement specimen. A two-dimensional axis-symmetry model for fluid flow and heat transfer in a wellbore is developed. The properties of the cement casing were obtained experimentally. The effect of downhole temperatures and velocities of the heat transfer fluid (oil) on the heat transfer and temperature distribution is evaluated and discussed in view of numerical results. The results revealed that the downhole velocity and temperature plays an insignificant role in affecting the cement outer wall temperature, justifying that the heat transfer within the wellbore is consistent. This indicates the potential of oil wellbores as sustainable geothermal energy resources. This study serves as a guideline for future researchers to design wellbore heat exchangers from depleted oil wells by highlighting the temperature distribution of the cement outer wall and the effects of downhole velocity and temperature. © 2018 Author(s).