Bottom Flow Field Simulation Of High Pressure Jet Drilling

High-pressure jetting drilling is one of the principal means of increasing ROP. Compared with conventional drilling, the breaking rock mechanism of high-pressure jetting drilling depends not only on bit teeth, but also on "hydraulic action". The high-pressure jet from the nozzle can play the role of removing cuttings and breaking rocks, and always keep the bottom hole clean, so the ROP can be improved.Based on the principle of high-pressure jet drilling and computational fluid dynamic, this paper established a mathematical model of the bottom hole flow field (jetting peed, bottom hole pressure, overflow velocity)of high-pressure jet drilling. After analyzing the geometric characteristics of ?311.15mm tri-cone bit, a solid model of three-cone bit was built by using a kind of 3D modeling software. By boolean operation, we got physical model of the downhole flow field, and devided the model into grid, then simulated the distribution of speed and pressure at bottom hole with different pump pressure and flow rate by numerical simulation. On the basis of the numerical simulation, we summarized the effect of the application of high-pressure jet drilling in the field, and proposed reasonable jet nozzle combinations and the parameters of drilling.The simulation of bottom hole flow field of high-pressure jet drilling shows that drilling fluid return through both the sidewall and cone gap, and the thickness of bottom overflow layer is 4?5mm. The bottom hole jet zone exists pressure gradient, which is good for flipping and migrating debris. The nozzle pressure loss is with an increase in pump pressure, and ROP improves most at the first stage (20-25MPa). Within a certain range, the jetting speed and bottom hole dynamic pressure are with an increase in flow rate, but the influence of flow rate to overflow velocity is not obvious. The bottom hole flow field of two nozzles combination is more asymmetric than that of three nozzles', so the two nozzles combination is superior to the combination of the three nozzles.This paper's study has a great theoretical and practical significance for understanding the mechanism how jetting drilling increases ROP and selecting reasonable nozzles combination and flow rate.