Numerical analysis of the impact flow field of multi-orifice nozzle hydrothermal jet combined with cooling water

Hydrothermal jet technology is a novel drilling technology and has just been studied for several years. This technology uses a high temperature and high velocity jet to break rocks and has the potential to be more efficiently advantageous than conventional techniques for deep hard formations and geothermal well drilling. This paper presents a multi-orifice hydrothermal jet model with cooling water to investigate the features of the flow field by CFD methods. First, a transient impact flow field is analyzed. Besides, influences of jet temperature, cooling water temperature and cooling water pressure on the flow field and annular cooling effect are predicted and compared. Predictions are found to be in good agreement with the published heat transfer theory for hydrothermal jet temperatures ranging from 650 K to 800 K. Results indicate that ambient cooling water envelops the high temperature hydrothermal jet in the middle. There is a second peak of bottomhole temperature and the pseudo-critical point is located. Controlling the hydrothermal jet temperature at the vicinity of the pseudo-critical point or far larger than the pseudo-critical temperature can have a better heat transfer effect. The simultaneous effect of both the hydrothermal jet and cooling water results in the non-uniform distribution of bottom temperature, which leads to higher rate of penetration. It is recommended that the cooling water pressure should be larger than the hydrothermal jet pressure, which might result in higher rate of penetration and cool the coiled tubing and borehole wall simultaneously. Results in this paper are beneficial to the parameters design for the hydrothermal jet drilling technology.