Numerical analysis of the downhole flow field with compressible fluid in hydrothermal jet drilling

A novel hydrothermal jet drilling technology is proposed, which is expected to be suitable for the exploitation of subsurface hydrocarbon resource or geothermal energy. The flow field is analyzed with compressible fluid. Influences of jet temperature, jet velocity, cooling water velocity, and cooling water temperature are discussed. Gray correlation method is used to compare the effects of different factors and further verification is performed. Simulation results are validated by results from experiments and analytical models. The values of specific heat are relatively high in the annulus because the hydrothermal jet undergoes the pseudo-critical point. Despite higher temperatures of the hydrothermal jet, the annular high temperature fluid can be effectively cooled. Considering both thermal effect and impact, it may be better to keep the hydrothermal jet temperature in the range of 700 K-800 K under the conditions of this paper. Under different cooling water velocities, the varying trend of the borehole wall temperature corresponds with that of the specific heat. The cooling water velocity has the most significant impact on the variation of the annular temperature, with the following sequence being jet temperature, jet velocity and cooling water temperature. Adjusting cooling water velocity may be the most efficient and cost-effective way for the hydrothermal jet drilling.