As hydrocarbon development goes deeper and more complex in Songliao Basin, drilling engineering has been put at the forefront of cost reduction and efficiency enhancement. The unique challenges resulted from high abrasiveness in hard igneous formations have triggered years of efforts for cost-effective percussive rotary drilling technology. This paper will highlight the development and application of a self-oscillation pulsed percussive tool, with in-depth analysis of its active mechanism and numerical modeling results of pressure and velocity distribution inside the self-oscillation chamber.

A two-stage oscillator designed on acoustic philosophy is introduced in the tool to create hydraulic pulse after resonance, feedback, frequency selection and amplification of high speed flow downhole. The pulse immediately induces the periodic impact against bit with high frequency and low amplitude using an appropriate hydraulic energy transfer structure. The pulsed jet, mechanical percussion and rotation are integrated to enhance breaking of hard rocks. The vibration frequency, peak value and amplitude can be adjusted with respect to oscillator geometry, size of drive spindle, and the distance between oscillator outlet and spindle top.

The elimination of moving part like conventional percussion hammer significantly simplifies tool structure, allowing better assurance of security and reliability in harsh environment. Primary test in South Songliao and extended application in Sichuan and Tarim Basin demonstrate that the tool can deliver improved ROP by 20%-36% compared with offset wells, prolonged percussion durability of more than 150 hours, enhanced deviation control capability, favorable erosion resistance and HT resistance rated to 200. Meanwhile, the pulsed jet through bit nozzles helps to improve hole cleaning and decrease rock's fracture strength.

The tool and related operational procedure provides a new enabler to conquer drilling challenges in igneous rocks, as well as in tight shale, sandstone and huge-layer of gravel encountered in China.

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