Experimental study on influence factors of wellbore self-circulation mining hot dry rocks

Abstract

The wellbore self-circulation technology, which exchanges heat through a U-channel composed of the oil tubing and casing, is a new technology used to exploiting geothermal energy from hot dry rocks. In this study a laboratory-scale simulation device is established to simulate the heat exchange process of local wellbore self-circulation in hot dry rocks. A series of laboratory experiments using water as heat transfer fluid are carried out to study the influencing factors and parameters of heat exchange. The experimental results show that the granite with larger heat mining capacity and heat capacity has higher heat mining rate at high temperature. In addition, increasing water injection rate will increase the heat mining rate but decrease the outlet temperature. Therefore, the balance between the higher outlet temperature and the higher heat mining capacity should be carefully selected. The similarity analysis shows that the 876-meter-long vertical well can obtain 565 kW heat mining capacity from hot dry rocks at 150 ℃ when the injection rate is 602.8 m3/d, which is very close to the field measured data and can prove the rationality of the similarity analysis results. The simulation device and experimental principle established in this study are also applicable to the middle and deep coaxial casing buried pipe heat exchange technology with characteristic of "taking heat without taking water", which can provide a certain reference for the research and practical application of middle and deep geothermal exploitation.

Keywords

• hot dry rocks
• wellbore self-circulation
• experimental simulation device
• heat transfer parameters
• similarity analysis