Improved Roller Cone Bit Selection Through the Use of an Attribute Based Bit Classification System
Authors: Parys P.G. , Langford J.W. , Berga P.K. 
Published: December 2007

SPE/IADC Members

The IADC roller cone bit classification system provides valuable general information but does not lend itself to being used as a specific bit comparison tool. Despite these limitations, the IADC code is often used (in the absence of an alternative method) to specify the required bits for a particular project or to select comparable bits from an alternative manufacturer.

The problem with this practice is that the code for roller cone bits is assigned on a completely arbitrary basis (other than bearing design or tooth material) by the manufacturer. The code is more specific with regard to formations than it is to cutting structure geometry. As a result, it is not uncommon for two manufacturers to produce vastly different bits sharing the same IADC code. Furthermore, varied drilling equipment and systems will often dictate that different bits be employed to drill the same formation in a given area. This paper describes an attribute based system utilizing six descriptive items which allow an objective comparison of bit geometry and cutting structures of specific sizes of bits from all manufacturers. The six items are: total/gage insert count, number of rows, extension and shape of drive rows, extension and shape of gage row, bit offset, bearing type, design of heel row including passive or active gage cutting features, and additional features with which the bit is equipped. These criteria can be objectively compared to provide insight when evaluating bit proposals, post well analysis, and most importantly, when comparing various manufacturers roller cone bits. Case studies will be presented that support the benefits of utilizing an attribute classification system.

Introduction

If an operator runs an IADC 5–1–7 from brand X resulting in premature broken teeth, he should not be anxious to try brand Y's IADC 5–1–7 which may have more offset, a more aggressive bottomhole profile and less inserts of a greater length. Although this example sounds like simple logic, this situation occurs every day in our industry. Drilling personnel and field sales personnel need to place greater emphasis on collecting, comparing, and disseminating specific bit attribute data on a more widespread basis.

There are individuals already doing this and their efforts should be applauded. One operator (the KTB deep scientific well) went so far as to record the outside diameter of specific cones to calculate cone revolutions rather than just bit revolutions. However, those that are making comprehensive attribute based comparisons of roller cone bits are by far the minority in our industry. In addition, manufacturers need to be more cooperative in making this information readily available to their field personnel and customers.

Attribute Based Classification System for Roller Cone Bits Anyone familiar with the IADC classification system for fixed cutter bits will have an appreciation of this concept. The fixed cutter classification system includes a wide array of objective criteria which include: body material, cutter type, bit profile, face design, type/number of jets and cutter size/density. This data allows drilling personnel to make a more objective comparison of bits than the traditional roller cone classification system allows. One could almost draw a picture of a particular type of PDC bit based upon knowing only the IADC code for that particular bit.

The most objective method of comparison of roller cone bits is an attribute based system that compares the varying geometry of a particular group of bits. The attribute based system outlined here, utilizes a six item classification system which allows an objective comparison of bit geometry and cutting structures of specific sizes of bits from all manufacturers. An example and description of the six items is as follows:

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