Experimental study on working mechanics of PDC bit with worn teeth

Abstract

PDC bits have been working in a worn state for a long time. To explore its cutting performance and avoid premature failure of the bit, this paper analyzes the load on the worn teeth and the drilling characteristics of the bit through single tooth cutting experiment and full-scale wear bit drilling experiment. The result shows that the worn teeth bear larger load compared with the new teeth, and the phenomenon of blunt rubbing is common in the process of rock cutting after the cutting teeth are “rounded”. Under the same depth, the greater the wear height is, the more obvious the load fluctuation appears. Through the full-scale bit drilling experiment, it is found that compared with the new bit, the worn bit can produce a smoother bottom hole, which is not beneficial for PDC bits' teeth intruding into the rock. With the increase of wear degree, the mechanical rate of penetration decreases and the mechanical specific energy increases. When the wear is greater than 3 mm, the mechanical specific energy and mechanical rate of penetration are not sensitive to weight on bit. With the increase of wear degree, the vibration degree of the bit decreases, and there is little difference in the radial acceleration value of the bit regardless of the wear degree.

Keywords

• cutting load
• single tooth cutting
• drilling characteristics
• mechanical specific energy
• mechanical penetration rate