Abstract
Torsional impact drilling is a new technology which has the advantages of high rock-breaking efficiency and a high rate of penetration (ROP). So far, there is no in-depth understanding of the rock-breaking mechanism for the ROP increase from torsional impact tools. Therefore, it has practical engineering significance to study the rock-breaking mechanism of torsional impact. In this paper, discrete element method (DEM) software (PFC2D) is used to compare granite breaking under the steady and torsional impacting conditions. Meanwhile, the energy consumption to break rock, microscopic crushing process and chip characteristics as well as the relationship among these three factors for granite under different impacting frequencies and amplitudes are discussed. It is found that the average cutting force is smaller in the case of torsional impact cutting (TIC) than that in the case of steady loading. The mechanical specific energy (MSE) and the ratio of brittle energy consumption to total energy are negatively correlated; rock-breaking efficiency is related to the mode of action between the cutting tooth and rock. Furthermore, the ROP increase mechanism of torsional impact drilling technology is that the ratio of brittle energy consumption under the TIC condition is larger than that under a steady load; the degree of repeated fragmentation of rock chips under the TIC condition is lower than that under the steady load, and the TIC load promotes the formation of a transverse cracking network near the free surface and inhibits the formation of a deep longitudinal cracking network.
Highlights
Torsional impact drilling (TID) is a new drilling technology developed on the basis of rotary drilling (SapinskaSliwa et al 2015)
Li et al (2016) experimentally investigated the fracture process of sandstone specimens containing a pre-cut hole under coupled static and dynamic loads, and the results show that the combined effects of stress concentration around the pre-cut hole and far-field strain generated by static loading promote rock impact damage
The particle flow code (PFC) is a micro-discrete element method (DEM), which is proposed by Cundall and Strack (1980) to simulate the motion and interaction of spherical particles
Summary
Torsional impact drilling (TID) is a new drilling technology developed on the basis of rotary drilling (SapinskaSliwa et al 2015). The invention of the Tork Buster TID tool makes it possible for polycrystalline diamond compact (PDC) bits to drill into deeper and harder formations at a Edited by Yan-Hua Sun. In the last 10 years, a large number of scholars have carried out some studies related to rock breakage and torsional impact rock breaking. Zhang et al (2011) had measured rock stress–strain behavior and rock deformation and strength characteristics under different rock conditions by triaxial stress tests They showed that the initial fractures influenced the rock crushing effect and the compaction effect influenced the rock mechanical properties. Based on the background of above TID technology in this study, DEM software (PFC2D) is used to compare the rock-breaking behavior of granite under steady and torsional impacting conditions. The energy consumption to break rock, microscopic crushing
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