Twin Edge Cutter (TEC) - Enhancing PDC Bit Development and Performance
Authors: Mensa-Wilmot Graham , Truax David 
Published: December 2007

Developments in Polycrystalline Diamond Compact (PDC) cutting elements (cutters) have tremendously improved PDC bit development and performance. Other factors such as bit profile, cutter layouts and hydraulic configurations have also contributed to the growing success of PDC bits.

In combination with the above, the drilling industry has also gained a better understanding on subjects such as vibrations, formation drillability, selection, capabilities and limitations of PDC bits. These have helped to remove the uncertainties that previously surrounded these bits, with regard to their performance expectations. PDC bits are drilling faster, longer, extending their application envelope and meeting the continuously changing drilling objectives of operators.

Bit development has to be taken to a much higher level, in order to improve on the current performance trends. This will require quantification of the factors and issues that have contributed to performance improvement, determination of the magnitudes of their contributions, the establishment and optimization of their associated relationships.

PDC cutters have had the biggest influence on PDC bit development and performance. In addition to enhancing performance, cutters permit optimization of the other factors that have contributed to the success of PDC bits.

This paper will present the new Twin Edge Cutter (TEC), which is setting new standards in PDC bit development and performance. The TEC cutter permits optimization of design features, and enables the development of customized PDC bits with extended application envelopes, that drill faster and longer.

Background

The locus on PDC bit development has shifted from a "curative" to a "preventive" process. This change had to occur, because the drilling industry now expects more from PDC bits.

During the curative era, products were sometimes developed before anyone knew where and how they were going to be used. Upon being run, "cures" were made to correct the bit's design deficiencies, without regard to the operator's drilling program, expectations and environment. The cures included changes to the bit's profile, cutter count, cutter size and blade count. Seldom were the relationships between the changes quantified, or expressed in terms of their contribution to an operator's bottom line. This approach tended to be tortuous, costly and, yielded very little benefit to the operator.

As PDC bit performance gradually improved, the industry's confidence in them as viable drilling tools increased. Researchers, in trying to establish the curative era's "missing relationships", and why PDC bits sometimes failed prematurely. Uncovered the subject of PDC bit vibrations.

Axial, torsional, lateral and whirl were identified as the vibrational modes. A lot of effort was spent, defining and quantifying PDC bit vibrations with regard to how they were initiated, sustained, propagated and amplified. The elaborate effort spent on this subject, helped define impact as the main failure mode of PDC bits. The industry began investigating and developing concepts that would prevent and or mitigate PDC bit vibrations.

Within the same time frame, formation drillability began to be quantified. Calculation of rock mechanical properties such as Poisson's ratio, bulk compressibility, internal friction angle, shear and compressive strengths became a norm rather that a rarity. The industry finally acquired the tools, needed to ensure a preventive approach to PDC bit development.

Regardless of the intent and objectives of the development, the preventive approach requires familiarization and a clear understanding of the following statements:PDC bit development has to be driven by the operator's drilling objectives and expectations.The design philosophy of a PDC bit establishes it's vibrational characteristics.

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