Research on the Step Drilling System for Water Jet Radial Drilling

The low traction force of the front-end nozzle for water jet radial drilling limits the drilling distance. The ground run drilling method has complex force transmission, large run-in-hole fluctuation, and has difficulty in the ground precise control of downhole drilling speed. In view of this, a step drilling system for water jet radial drilling is studied. The system realizes the low-speed drilling of the nozzle through the low-speed drilling controller, and ensures the continuous drilling of the nozzle through the step anchor feeding mechanism. The step anchor feeding mechanism has a feeding distance of 2 m each time, and the drilling distance of the nozzle is equal to the feeding distance multiplied by the feeding times. Increasing the feeding times can achieve long-distance drilling. After the drilling is completed, reduce the system pressure, and the step anchor mechanism releases the anchor. Then use a coiled tubing to lift the tool out of the wellbore. When jet drilling, the pushing speed (v1) of the nozzle is consistent with the rock breaking speed (v2) of the jet, and the rock breaking effect is good. If v1 > v2, it will cause the nozzle to collide with the end of the hole, causing the jet hose to bend and block in the hole, ultimately preventing long-distance drilling; If v1 < v2, the nozzle jet will excessively cut in the hole, forming a cavity, and the hole will lose its righting effect on the nozzle, leading to drilling deviation. The test results show that the system can realize jet drilling in the formation at low speed (0.5–3.0 mm /s), high thrust (2 KN) and long distance (≥10 m) drilling. The system's drilling speed is consistent with the jet breaking rock velocity (0.3–5.0 mm /s), which can maintain a relatively stable jet distance between the nozzle and the rock, and this is conducive to long-distance drilling. Under shallow burial depth, soft rock, large porosity, and low confining pressure and high temperature conditions, rock-breaking drilling efficiency is high, and vice versa. This article reveals the relationship between nozzle pressure drop, jet impact pressure, and rock critical pressure during water jet radial drilling. Analyzed and summarized several key factors that affect drilling efficiency, and creatively designed a step drilling system for water jet radial drilling. Several types of oil reservoir blocks that are easy to implement jet drilling were recommended. The research results can provide a certain reference for further research and application of jet drilling technology.