Abstract
Extensive studies have been carried out on cutting rock with a PDC cutter, but cutting rock assisted by impact force is rarely studied. In this paper, cutting rock using conical and cylindrical PDC cutters assisted by impact force were researched with the explicit dynamic model. The laws of cutting rock using a cylindrical cutter assisted by impact force are the same as those of a conical cutter. There are thresholds of impact frequency and amplitude when they are single variables. When impact frequency is lower than the threshold frequency, the impact frequency is the dominant frequency in the frequency spectrum of weight on bit (WOB), and the amplitude of dominant frequency and removal volume decreases with the increase of impact frequency. When the impact frequency is higher than the threshold frequency, there is no dominant frequency in the frequency spectrum of WOB, and the removal volume behaves the same. When the impact force is lower than the threshold amplitude, there is no dominant frequency in the frequency spectrum of WOB, and it does not affect the removal volume but the removal volume is positively correlated with the impact amplitude. When the impact amplitude is higher than the threshold amplitude, the removal volume is also positively correlated with the impact amplitude, and the removal volume assisted by low-frequency (20 Hz and 40 Hz) impact force is higher. The frequency threshold and amplitude threshold of the conical cutter are smaller than those of the cylindrical cutter. Although the cutting depth and removal volume of the conical cutter are lower than those of the cylindrical cutter, the amplifications of cutting depth and removal volume of the conical cutter are higher than those of the cylindrical cutter when assisted by impact force.
Highlights
In the process of oil and gas exploration, there are some problems such as low rate of penetration (ROP), short pure drilling time and long drilling cycle in hard rock, and abrasive formation with poor drillability
Ere are some experiments and field applications of the conical cutter [7, 20], but there is no research on the conical cutter and the cylindrical cutter cutting rock assisted by the impact force. erefore, the research on the cutting rock law of conical and cylindrical cutters assisted by the impact force is beneficial to expand the application of the conical PDC cutter and further improve drilling efficiency
To express the axial impact force, the weight on bit (WOB) equation can be expressed as follows:where k is the impact frequency, p is the impact amplitude, and w0 is the static value of WOB. e conical cutter and the cylindrical cutter were firstly used to simulate the process of cutting rock assisted by the impact force. e static WOB is 900 N, the cutting speed is 0.8 m/s, the impact frequency is 20 Hz, and the impact amplitude is 1000 N
Summary
In the process of oil and gas exploration, there are some problems such as low rate of penetration (ROP), short pure drilling time and long drilling cycle in hard rock, and abrasive formation with poor drillability. Ere are extensive research studies and applications of the impact force on the cylindrical PDC cutter [13,14,15,16,17,18,19]. Ere are some experiments and field applications of the conical cutter [7, 20], but there is no research on the conical cutter and the cylindrical cutter cutting rock assisted by the impact force. Erefore, the research on the cutting rock law of conical and cylindrical cutters assisted by the impact force is beneficial to expand the application of the conical PDC cutter and further improve drilling efficiency. In this paper, based on the explicit dynamic method, the effect of the impact force on the conical cutter and cylindrical cutter cutting rock is studied with the Holmquist–Johnson–Cook model
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