Comparative Thermodynamic Optimization of Organic Rankine Cycle Configurations for Geothermal Power Generation from an Abandoned Oil Well

Abstract

This study was aimed at quantifying the net electrical power producible from an abandoned oil well in Nigeria using different organic Rankine cycle (ORC) configurations and working fluids. The geological features of a typical Nigerian oil well were employed in the study and a borehole heat exchanger was used for simulating the thermodynamic parameters of the heat source. Specifically, a subcritical ORC without a recuperator (SBC), a subcritical ORC with a recuperator (SBC-R), a supercritical ORC without a recuperator (SPC), and a supercritical ORC with a recuperator (SPC-R) were analyzed, using R115, R236fa, and R1234yf as working fluids. Results showed that between 272 kW and 875 kW of electrical power could be produced from the abandoned oil well using the most basic ORC configuration (SBC). Furthermore, it was obtained that the introduction of a recuperator would increase the ORC net power by about 13% for R236fa, 33% for R1234yf, and 107% for R115. Similarly, a switch from a subcritical ORC to a supercritical ORC configuration would increase net power for all the working fluids. Specifically, an increase in net power was estimated at 3.6% for R236fa, 46% for R1234yf, and 152% for R115 regarding a switch from the SBC to the SPC. Moreover, decreasing the condensation pressure of the ORC plants was observed to improve net power in all cases.