Abstract
Abstract Based on the principle of wellbore self-circulation heat mining, the evaluation experiments of local wellbore self-circulation heat exchange laws and influencing factors were carried out. Water, SCCO2, R134a, and heat transfer oil were screened as the heat-carrying fluids. The heat exchange laws and heat mining capacity of these four heat carrying fluids were analyzed and compared, and their heat mining rates at the field scale were estimated using the similarity criterion method according to the experimental results. The results show that R134a and heat transfer oil can obtain the largest outlet temperature and the largest heat loss ratio, while the water can achieve a higher heat mining rate and a larger convective heat transfer coefficient than the other three fluids. The heat mining capacity of CO2 is significantly affected by the injection pressure. It is necessary to optimize the injection pressure larger than critical point to achieve the best heat mining performance. When the water is selected as the heat-carrying fluid, the heat mining rate can reach more than 1 MW if a horizontal wellbore with a length of 2000 m is applied for wellbore self-circulation at the field scale.
Highlights
Geothermal energy is one of the promising renewable energy resources [1,2,3,4,5]
MPa; (4) the injection rate is 107 ml/min; (5) the heat insulation condition of the tubing is vacuum insulation; (6) water, SCCO2, R134a, and heat transfer oil are selected as the heat-carrying fluid
We selected the SCCO2, R134a, and heat transfer oil to carry out the wellbore self-circulation heat exchange comparison experiment and analyzed the heat exchange law and the difference of heat mining capacity of different heat-carrying fluids
Summary
Geothermal energy is one of the promising renewable energy resources [1,2,3,4,5]. Hot dry rock (HDR) is the most attractive geothermal type, which has the advantages of high temperature, wide distribution, and large reserves [6, 7]. A large amount of water is injected into the reservoir as a heat-carrying fluid. Through water circulation and heat exchange with hot rocks [9, 10], geothermal energy is extracted for power generation. This process is called Enhanced Geothermal System (EGS). The research on HDR EGS has been conducted for more than 40 years, there are still the following main problems: (1) loss of heat-carrying fluid; (2) fluid flow channel blockage caused by rock-fluid interaction, resulting in reduced heat mining efficiency; (3) economic costs are high and commercial operation is difficult; (4) EGS may induce earthquake and environmental problems. New simple and economical HDR geothermal mining technologies are needed [4, 11,12,13,14,15,16]
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