Cascade utilization of low temperature geothermal water in oilfield combined power generation, gathering heat tracing and oil recovery

Oil wells at the high water-cut stage are used as geothermal wells and geothermal power plants in oilfield have their own advantages. A new compound system combining the organic Rankine cycle (ORC) plant with the gathering heat tracing (GHT) station and the oil recovery system is presented. First, the exergy destruction of the system is calculated and the reason for the low efficiency of the ORC with R123 is pinpointed through exergetic analysis. The plant is optimized numerically and working fluids investigated are R601a, R601, R123, R141b, R245fa, and R600. A new objective function is defined, reflecting both technical and economic performances. The feasibility of replacing oil boilers with geothermal water is then analyzed. Finally, the overall economic performance is calculated. Results show that the exergy destruction of the ORC with R123 is the highest. The optimized plant with R601 a increases the net power output by about 40%. About 8163 tops of oil is saved and about 34.6 thousand tons of oil is recovered per year. The payoff period is only about 3.2 years whereas it will be sharply shortened if the earnings of oil are also considered. The new system is rational in technology and profitable in economy, which can be used as a way to increase economic benefits for oilfields at the high water-cut stage. (C) 2012 Elsevier Ltd. All rights reserved.