Simulation of a novel deep ground source heat pump system using abandoned oil wells with coaxial BHE

Abstract

As one of the most important geothermal applications, ground source heat pump (GSHP) systems have been applied for spacing heating and cooling of buildings, and the abandoned oil wells (AOW) with deep depth contain abundant geothermal energy. Therefore, this study proposed a new GSHP system using single AOW, and the deep coaxial borehole heat exchanger (BHE) with insulation is introduced to retrofit the wellbore of AOW for heat extraction. At first, a comprehensive heat transfer model for the deep coaxial BHE combing fluid, borehole and ground was built to evaluate the performance of the proposed GSHP systems during annual run. Then, Monte Carlo method was used for parameters sensitivity analysis to obtain the PRCC determining the intensity of parameters effect on total system COP. Lastly, the optimization of injection parameters was performed. The results indicated that flow rate showed the strongest influence on the total system COP. During the annual operation, it was found that the mean heat supply by the AOW-GSHP system was about 384 kW, and reached to 192 kW/m for unit depth which was obviously higher than that in conventional GSHP. And the mean heat extraction from AOW by the AOW-GSHP system reached to 294 kW, more than that by directing heating using AOW. By the optimization, it was found there was optimal inlet temperature getting maximum system COP and it existed a minimum injection pressure supporting system operation.