Petroleum Drilling Techniques, Issue 4, 2018

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The Rock Breaking Mechanism of Ultrasonic High Frequency Rotary-Percussive Drilling Technology

Abstract

The ROP of the traditional drilling in deep hard formations is very low, which seriously affects the process of exploration and development of deep and ultra-deep oilfields. To solve this problem, ultrasonic high frequency rotary-percussive drilling technology was proposed, and the ultrasonic vibration pup joint for realizing the ultrasonic high frequency rotary-percussive drilling was designed by combining the ultrasonic rock breaking technology with the traditional rotary rock breaking technology. Employing geomechanical theories, the rock breaking mechanism of ultrasonic high frequency rotary-percussive drilling was analyzed and a high frequency percussive drilling model was established. Through dimensionless numerical analysis of the high-frequency percussive drilling mathematical model, the three stages of high-frequency percussive drilling were studied, and the influence of key parameters, including weight on bit, frequency and amplitude, on rock breaking efficiency were analyzed in detail. It was observed that the rock breaking efficiency increased as the weight on bit and amplitude increased, and there was an optimal vibration frequency, resulting in the highest rock breaking efficiency. The results showed that the ultrasonic high frequency rotary-percussive drilling technology improved the ROP in deep hard formations by accelerating the fatigue breakdown of hard rocks, reducing the bit stick-slip vibrations and reasonably utilizing resonance energy.