Air-Lifting Reverse-Circulation Drilling in Deep Geothermal Wells and the Effect of Dual-Wall Drill Pipe Depth Down the Hole

Geothermal energy is a renewable energy source that is rich in reserves, widely distributed, stable and reliable. The development of geothermal energy needs to be carried out by drilling wells to exploit the underground thermal fluid, and air-lift reverse circulation drilling technology has the advantages of protecting the thermal reserves and reducing costs in the development of geothermal energy. In this paper, based on the working principle of air-lift reverse circulation drilling, combined with the single-phase liquid, liquid–solid, gas–liquid–solid three-phase fluid mechanics theory, the pressure model of air-lift reverse circulation in geothermal deep wells is established. The influence of the depth of dual-wall drilling rods on the lifting force and total friction loss pressure of air-lifting reverse circulation is analyzed, and it is proved that there is an optimal value of the depth of dual-wall drilling rods, which provides a theoretical basis for selecting a suitable depth of dual-wall drilling rods in the construction of air-lifting reverse circulation in geothermal deep wells.