An Easy-To-Use Method for Tracking Rock-Bit Wear While Drilling

One key factor in minimizing drilling costs is knowledge of rock-bit behaviour at the bottom of the well and particularly the state of bit wear. This paper describes a method giving information about bittooth wear while drilling. The basic concept requires the following torque equation that is a function of weight-on-bit (W),TOB = uW + vW²This equation is determined from measurement-while-drilling data, and knowledge of v provides the bit wear state, given the close correlation between these two parameters. Therefore a chief difficulty in the question is to find such a correlation. The theoretical approach, many laboratory drilling tests, and some fields results are described. Laboratory tests and field results have quantitatively confirmed the validity of the concept. It was found that v decreases as a quasi-linear function of bit wear and accordingly may be considered as a real-time wear criterion. Moreover the value of v is moderately affected by formation type. In the harsh economic environment of today, field applications of the method should lead to more accurate decisions as to when to pull out bits and thus to a reduction of drilling costs.