Issue34

J. He et alii, Frattura ed Integrità Strutturale, 34 (2015) 564-573; DOI: 10.3221/IGF-ESIS.34.62 572 The moving particles of drilling muds in a fluidic amplifier are distributed as shown in Fig. 7. The particles of drilling muds principally aggregate in the jet nozzle, and the jet nozzle is the first contact area between drilling muds and the amplifier. It can be concluded that the most severely abraded position of a fluidic amplifier is the jet nozzle, afterwards are the lateral plates and the wedge of the fluidic amplifier due to the high velocity as well as pressure of the drilling muds. Simulation results show extraordinary agreements with the actual cases of a fluidic amplifier in directional well drilling. Interpretation can be drawn that the moving velocity of drilling muds contact with the lateral plates is relatively lower than the main jet due to the wall-attachment effect, the action time of solids in drilling muds is increasing, leading to the increase of erosion on lateral plates of a fluidic amplifier. In addition, the wedge of a fluidic amplifier is eroded by drilling muds with a large incision angle, thus the erosion of the wedge in a fluidic amplifier is serious, which needs more attention in the operation of drilling process. Effects of Jet Velocity of Drilling Muds on Anti-erosion Property The effect of jet velocity of drilling muds on erosion rate of a fluidic amplifier has been analyzed by 2#, 4# and 5# drilling muds, i.e. the particle size and solid content are constant while the simulation with various drilling muds is conducted. As shown in Fig. 8, it can be concluded that erosion rate of a fluidic amplifier is approximately exponentially increases with the jet velocity. The effect of jet velocity and solid content of drilling muds show great agreements on the erosion rate of a fluidic amplifier. Figure 8 : Erosion rate of drilling muds on a fluidic amplifier varies with jet velocity. The maximum erosion rate is 5 8.9 10   while the jet velocity is less than 75 m/s. While the jet velocity is increasing by 15m/s, the deviation of erosion rate on the fluidic amplifier increases nearly 2 times allowing for the fitted erosion rate. Thus in the design of a fluidic amplifier, the jet velocity should be less than 75 m/s in order to improve the service life time of hydraulic hammers with a fluidic amplifier. C ONCLUSIONS 1) The effects of particle size, solid content and jet velocity of drilling muds on anti-erosion of a fluidic amplifier has been numerically studied by simulation models and analysis. 2) The erosion rate of drilling muds on a fluidic amplifier nearly linearly varies with the particle size of drilling muds, and almost exponentially varies with solid content and jet velocity of drilling muds. 3) It can be concluded that the jet nozzle of a fluidic amplifier is primarily abraded, afterwards are the lateral plates and the wedge of the fluidic amplifier. Simulation results have shown good agreements with actual cases in drilling process.