An optimization of acquiring geothermal energy from a deep geothermal well by downhole coaxial open loop (DCOL)

Abstract

As one of the methods to extract geothermal energy, downhole coaxial heat exchanger is widely concerned because of its high heat extraction rate and no need of re injection. However, there are few studies on the extraction of open-loop heat from a single deep geothermal shaft, and there is a lack of detailed inlet and outlet transient temperature data. In this study, the downhole coaxial open-loop heat collector is improved, and the slotted liner at the bottom of the well is used to form a free open space to improve the heat exchange. Using the improved experimental device design, the field thermal recovery test was carried out in deep geothermal well of Shengli Oilfield, Dongying, China. According to the field test results, the control equation was established, and the influence of parameters on the thermal recovery rate was studied. It is found that the improved heat output is greater than the reported value of the downhole heat exchanger with the traditional structure. After about eight days, the heat extraction rate reached a gradually stable stage. After 15 days of continuous operation, the heat output is stable at 200 kW, and the water temperature at the water outlet is 34.6 °C.