Measurement of forces, temperatures and wear of PDC cutters in rock cutting

Abstract

The introduction of PDC bits in the oil well industry by General Electric in 1973 was a significant advancement in drilling technology. To understand the potential of these bits, cutting mechanics and heat transfer models were previously developed. In the current work a series of cutting experiments was made on granite rock in order to understand better the effects of cutter temperatures and forces on PDC bit life, especially the existence of a critical temperature. The experiments consisted of cutting granite cylinders on a lathe with a single PDC cutter. During the tests, cutter forces were measured with a lathe dynamometer and cutter temperatures were measured with thermocouples mounted on the cutter. The cutting fluid used was either an air jet, air mist jet or a water jet. The force and temperature data were recorded by a computer data acquisition system, and wear profiles of the cutters were determined by measurements with dial indicators. A new cutter wear model has been developed from the cutting experiments, and the theory agrees well with experimental data. It has been learned that cutting of hard formations is possible by controlling the temperature of PDC cutters, within the critical limit, with an adequate amount of cooling. Another significant result is that the contact stress on the carbide is not negligible, which is contrary to what was previously believed. This is a practical disadvantage for drilling because it leads to higher forces on the cutters. This often results in lower penetration rates because of bit weight limitations.