Abstract
Hybrid impact drilling is a new drilling method proposed in recent years, the PDC (polycrystalline diamond compact) bit impacts the rock in torsional and axial directions during its rotation. From the perspective of field application, hybrid impact drilling can increase the rate of penetration (ROP), especially in hard heterogeneous formations. However, its rock breaking mechanism and difference from torsional impact drilling are not clear, this leads to aimless in choosing these two drilling methods. In this paper, the quasi-3D numerical simulation model of hybrid impact cutting is carried out to investigate the rock breaking mechanism, including the chip formation, mechanical specific energy (MSE) etc. moreover, its comparison with torsional impact cutting is also conducted for evaluating the applicability of these two methods for the same formation. The results show that, the rock breaking efficiency of hybrid impact cutting is higher than torsional impact cutting for shallow depth of cut (DOC), on the contrary, the rock breaking efficiency of hybrid impact cutting is more lower for the medium DOC; but for the deep DOC, both of these two cutting methods cannot improve the rock breaking efficiency. The axial impact amplitude and frequency have large influence on rock breaking efficiency, the optimal axial impact amplitude and frequency exist for specific formation. Both of these drilling methods are not applicable to soft formations. This study leads to an enhanced understanding of rock breaking mechanisms in hybrid impact drilling, and contributes to the improvement in the design of impact tools and determination of the related parameters.
Highlights
PDC (Polycrystalline diamond compact) bit has been widely used in geological exploration due to its high drilling speed, long working life, good stability and flexible design etc
The quasi-3D numerical simulation model of hybrid impact cutting is performed through the trial and error calibrations using experiment results to investigate the rock breaking mechanism, including the cutting force responses, chip formation, mechanical specific energy (MSE) etc., its comparison with torsional impact cutting is conducted for evaluating the applicability of these two methods for the same formation
The results show that the magnitude of MSE is the smallest when the impact amplitude is 0.1 mm, it indicates that the axial impact amplitude is no need too large because it cannot induce corresponding rock breaking volume, resulting in the relatively large MSE eventually
Summary
PDC (Polycrystalline diamond compact) bit has been widely used in geological exploration due to its high drilling speed, long working life, good stability and flexible design etc. Zhu et al [9, 10] have investigated the effects of high frequency torsional impacts on rock drilling, the numerical simulations and experiment tests were carried out in these analysis. The main objective of this study is investigating the rock breaking mechanism of hybrid impact drilling, analyzing its difference from torsional impact drilling For this purpose, the quasi-3D numerical simulation model of hybrid impact cutting is performed through the trial and error calibrations using experiment results to investigate the rock breaking mechanism, including the cutting force responses, chip formation, MSE etc., its comparison with torsional impact cutting is conducted for evaluating the applicability of these two methods for the same formation
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