Evaluation of working fluids for geothermal power generation from abandoned oil wells

Geothermal power generation from abandoned oil wells is a new way to utilize geothermal energy. The organic Rankine cycle is used for exploiting geothermal energy from abandoned oil wells efficiently. The investigation on influences of working fluids on the power generation efficiency is significant. An analysis model for geothermal power generation based on the transient formation heat conduction of abandoned oil wells is presented in this paper. For abandoned oil wells with different kinds of well depths and geothermal gradients, the power generation performances using various organic fluids are analyzed. Direct power generation system (DPGS) is compared with flashing power generation system (FPGS). The results show that the geothermal energy from the abandoned oil wells with well depth less than 3000 m is worthless to be exploited due to low power generation efficiency. For the abandoned oil wells with well depths larger than 3000 m and geothermal gradients higher than 0.04 K/m, DPGS efficiency of supercritical working fluids leaving the recovery well is higher than FPGS efficiency of subcooled working fluids. R134a and R245fa are more suitable than R600a, R600, propylene, R290 and R143a for the geothermal power generation using abandoned oil wells.