Geothermal energy development is of critical importance to meet the global challenge of energy transition. This work demonstrates that existing oil and gas industry tools can be used to evaluate the potential of geothermal energy production from mature oilfields using the heat contained in the produced fluids. This can contribute to a decarbonation strategy and be profitable since most of the costs (drilling, pumps…) are already supported by oil production operations. The only additional costs consist in surface facilities to convert thermal energy into electricity. The aim of the study is to evaluate the potential of a mature oil field to generate electricity and predict the evolution of energy potential with time considering the current development plan for the field. This plan was designed to maximize oil production in the field and did not consider possible electricity cogeneration from geothermal energy. The study was conducted in a sector of a mature oilfield including 15 producers currently producing about 10,000 barrels of liquid per day and with a 97% water-cut. A workflow was created to estimate the potential of electricity generation considering current and forecast liquid production rates, the nature of the secondary working fluid used in the Organic Rankine Cycle (ORC) and the minimum ejection temperature limits, defined by the operator, to avoid difficulties in surface separation processes. This paper describes the surface process used for thermal energy to electricity conversion, and presents the workflow used to estimate electricity generated from simulation results considering uncertainty tied to some fluids and rocks parameters.