Operator Recommendation for a Uniform Dull-Grading System for Fixed-Cutter Hole-Enlargement Tools
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 139870, ’Operator Recommendation for a Uniform Dull- Grading System for Fixed-Cutter Hole- Enlargement Tools,’ by L. Ulvedal, SPE, Statoil, and J.D. Enterline, SPE, D. Scott, SPE, S. Radford, SPE, J. Clinkscales, L. Shale, and M. Croxton, Baker Hughes, prepared for the 2011 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 1-3 March. The paper has not been peer reviewed.
To standardize and permit the accurate dull grading of fixed-cutter bits, an International Association of Drilling Contractors (IADC) standard system was defined and implemented in 1987, with revisions in 1992. With hole enlargement becoming a fast-growing sector in the drilling industry, there is a greater need for an accurate and uniform dull-grading system for fixed-cutter hole-enlargement tools. Through collaboration between an operator and a bit manufacturer, a new dull-grading protocol is proposed to characterize hole-enlargement-tool dull conditions better. Adoption of this new dull-grading system for fixed-cutter hole-enlargement tools would facilitate an industrywide standard to communicate dull conditions more accurately.
Introduction
Because the oil and gas industry is familiar with the current IADC fixed-cutter-bit dull-grading system, service companies and operators often use a variation of this system to grade hole-enlargement tools. With these tools becoming increasingly advanced and as more designs are introduced, a new dull-grading system needs to be developed to evaluate these tools’ unique features and applications more consistently. The system to grade reamers uniformly must allow those without visual reference to the tool to have an accurate description of the dull condition.
The first objective is to establish a means to evaluate reamer dullness. The second objective is to provide uniformity and simplicity. This uniformity should be in use of similar terminology, format, and scales for grading reamer dullness. To gain industry acceptance, the new grading system should be consistent with current bit formats and provide adequate detail of the subject reamer. The simplicity will come from the recommendation to use the current dull-grading system established for bits, with minor additions for use with reamers.
History
Hole enlargement has been used in the oil and gas industry for nearly a century, with initial tools designed as fixed-blade concentric tools used to enlarge or clean previously drilled boreholes. These tools have evolved to include bicenter, eccentric, and concentric-expandable tools, each with specific design aspects.
Bicenter and eccentric tools were developed because of a need to expand boreholes below a restriction, such as a blowout preventer or casing. These tools enlarge boreholes to prevent issues with sloughing, swelling, and tectonically stressed formations. Eccentric reamers are fixed-blade tools with an offset cutting structure used to enlarge the borehole by centralizing the rotation of the tool body and forcing the eccentric cutting structure into the formation to enlarge the borehole. Bicenter bits are single-piece tools combining a pilot bit with eccentric-reamer blades.