Abstract
Self-circulation wellbore is a new technique for geothermal development in hot dry rocks (HDR), which uses a U-shape channel composed of tubing and casing as the heat exchanger. In this study, a self-circulation wellbore in HDR on a laboratory scale was built, and a serial of experiments were conducted to investigate the heat exchange law and the influencing factors on the heat mining rate of the wellbore. A similarity analysis was also made to estimate the heat-mining capacity of the wellbore on a field scale. The experimental results show that the large thermal conductivity and heat capacity of granite with high temperature can contribute to a large heat-mining rate. A high injection rate can cause a high convective heat transfer coefficient in wellbore, while a balance is needed between the heat mining rate and the outlet temperature. An inner tubing with low thermal conductivity can significantly reduce the heat loss to the casing annulus. The similarity analysis indicates that a heat mining rate of 1.25 MW can be reached when using a 2000 m long horizontal well section in a 150 °C HDR reservoir with a circulation rate of 602.8 m3/day. This result is well corresponding to the published data.
Highlights
Geothermal energy is one of the most promising renewable energies [1]
For convenience, the similarity of the casing annulus in a horizontal self-circulation wellbore was considered assuming that the inner tubing is totally adiabatic and the reservoir temperature around the wellbore is constant (If the heat loss from the inner tubing is considered, the estimated heat mining rate will be reduced by 5–10% on a field scale [11,16])
The experimental results indicate that the reservoir type, reservoir temperature, injection rate experimental results that athe reservoirinfluence type, reservoir temperature, rate and andThe the insulation of the innerindicate tubing have significant on the heat exchange injection law and the the insulation of the inner tubing have a significant influence onconductivity the heat exchange and the heat mining rate of the self‐circulation wellbore
Summary
Liang Zhang 1,2, * , Songhe Geng 1,2 , Jun Kang 1,2 , Jiahao Chao 1,2 , Linchao Yang 1,2 and Fangping Yan 3, *.
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