PDC Bits: All Comes from the Cutter/Rock Interaction

Abstract

PDC drill bit performances in hard rock has been greatly improved during the last decades by innovations in PDC wear, impact resistance and better vibrations understanding. The bit design is generally done by balancing the bit, distributing uniform wear along the profile and achieving high drillability and steerability. To obtain required drilling performances, drill bit designer adjust features such as profile shape, gage and mainly cutter characteristics (shape, type and orientation). Cutter rock interaction model became a critical feature in the design process. But previously used models considered only three forces on a cutter based on the cutter-rock contact area : drag force, normal force and side force. Such models are no longer valid with the introduction of PDC cutters with chamfer and special shape. This paper presents a new cutter rock interaction model including some several improvements. It is based on the presence of a build-up edge of crushed materials on the cutting face often described in the literature. In addition, the chamfer, which significantly affects bit Rate Of Penetration (ROP), is taken into account (shape and size). Forces applied on the back of the cutter and due to the rock deformation and back flow of crushed materials are considered in the model. Finally, results of numerous single cutter tests (under atmospheric and confining pressure) are presented and compared to the new cutter rock interaction model predictions. An analysis of the influence of the PDC characteristics (shape, size, chamfer, back and side rake angles, ….) is presented. The model has been applied to optimize the cutting efficiency and bit steerability and some design rules are given to minimize the specific energy and maximize the rate of penetration. Finally, full scale laboratory drilling tests and field results indicate that the use of accurate cutter rock interaction model can help the drill bit designer to find the best drill bit for a specific application. Standard laboratory full scale drilling procedures have been developed. The tests have shown that drillability, stability, steerability and wear can be improved and controlled by acting on the cutter characteristics, cutter setup, trimmer characteristics and gage type.

Mitigating Stick-Slip in Deep Drilling Based on Optimization of PDC Bit Design

“…Furthermore, it contradicts the classical static assumption which states that cutting forces do not depend on the cutting velocity [31]. Indeed, most existing cutting models are static [37,12,11,30,16].…”

A study on PDC drill bits quality

“…Operating parameters as weight and torque on bit, defined for a constant penetration speed, could be considered as independent of the number of bits [7]. This condition is assumed by a correct cutters repartition on the bit, which ensures a homogenized wear on every PDC [8]. Therefore, wear behavior and drilling performance information based on single cutter experiments are relevant and can be extrapolated to understand the whole tool behavior.…”

Weight Distribution in Reaming While Drilling BHAs

“…The assumption of the bit being a cylinder and not a discrete number of blades implicitly assumes the cutting force at each cutter to increase linearly with its tangential velocity. In literature (Langeveld 1992;Neubert 1997;Gerbaud 2006;Ernst 2007) it can be found that the velocity of a cutter does not influence the cutting forces. Cutting forces are nearly only dependent on the orientation of the cutter and the depth of cut DOC.…”

“…This is not the case for bit aggressiveness. In literature several cutter force models can be found showing the force at a cutter being only dependent on the area of cut and being independent of the cutter velocity, see (Langeveld 1992;Neubert 1997;Gerbaud 2006;Ernst 2007). The blade aggressiveness regards these general cutting force model assumptions and in this way provides a complete separation of the influences of drilling diameters D and cutting structure aggressiveness µ.…”