The cost to implement geothermal energy is extremely high, due to the requirement of drilling production and reinjection wells. One method to overcome this problem is to retrofit abandoned oil wells with a closed loop system, eliminating the need for drilling entirely. This study is conducted to evaluate the heat transfer performance of the wellbore heat extractor with the triangular protrusions. A two-dimensional axis-symmetry computational model for fluid flow and conjugate heat transfer in the wellbore is developed. The effect of protrusion height, pitch and volume flow rate are evaluated and discussed in view of numerical results. The results suggest that triangular protrusions offer higher heat transfer rate. However, careful consideration should be taken as the pumping power required is higher due to higher pressure drop. The outcome of this study provides a new insight into the development of geothermal energy, especially on the utilization of abandoned oil wells. © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 - The 10th International Conference on Applied Energy.