Experimental Investigation of the Rock Cutting Process with Blunt Pdc Cutters

Abstract

Wear of drill bit is a common and unavoidable phenomenon in drilling process, which not only reduces the aggressiveness of drill bit, makes it difficult for the drill bit to penetrate into the rock, but also further reduces the rock-breaking efficiency and prolongs the well construction period, which is extremely obvious in the drilling process of deep strata and hard strata. In addition, the complexity of bottom hole environment (BHE) also leads to the complexity of drill bit wear mechanism, resulting in the unclear rock-breaking behavior and mechanism of worn cutter. Therefore, in order to study the influence of bit wear on rock-breaking performance and explore the rock-breaking behavior of blunt cutter, in this paper, sandstone was selected as the experimental object, and a series of indoor rock cutting experiments were carried out with PDC blunt cutter obtained by mechanically cutting, and the influence of cutter wear on the rock-breaking process was studied from the aspects of cutting force, mechanical specific energy (MSE), cuttings and cutting grooves. The results show that, compared with sharp cutter, the forces and MSE of blunt cutter are increased during cutting. In addition, the wear of cutter reduces the aggressiveness of cutter, and the aggressiveness of cutter is decreased with the aggravating of wear of cutter. Similarly, the wear of cutter leads to the increase of cutter-rock contact area, resulting in a greater squeezing and grinding effect on rocks, which leads to the reduction of the size of cuttings and the production of more powdery cuttings during cutting. Besides, the cutting groove obtained by blunt cutter is rougher and wider than that obtained by sharp cutter; Moreover, the cutting groove obtained by sharp cutter is smoother and deeper. The experimental research results can provide relevant guidance and enlightenment for the study of rock-breaking behavior and the understanding of rock-breaking mechanism of worn cutter.

Keywords: drilling bit, Wear, Rock-breaking performance, Rock cutting experiment, Cuttings, Cutting groove