Rock fragmentation mechanism and drilling performance of harmonic vibration-impact drilling technique

Key words:  harmonic vibration-impact drilling  vibration response  rock fragmentation mechanism  numerical simulation  field case study

Abstract:

The harmonic vibration-impact drilling technique can be applied to increase the penetration rate and drilling efficiency. In this study, its rock fragmentation mechanism and drilling performance were investigated based on a micro-vibration model of rocks, in which the displacement and energy response equations of rocks were derived by taking into account of the damping effect of rocks. The rock fragmentation mechanisms under harmonic vibration-impact and resonance impact were analyzed respectively. In addition, the stress state in rock matrix and the axial and torsional movement characteristics of the drill bit under harmonic vibration-impact were studied using a finite element software. A field case study of well S was applied to verify the drilling efficiency of the harmonic vibration-impact drilling technique. The results show that, due to the alternating stress under harmonic vibration-impact, rock matrix is more vulnerable to subject to tensile and fatigue fragmentation. Under the condition of resonance impact, the vibration response of rock matrix can reach a maximum state, which can induce instantaneous rock fragmentation. Meanwhile, the harmonic vibration-impact can alleviate the stick-slip effect of the drill bit and speed up the penetration rate, and improve the drilling performance.