New Generation Of Oilfield Bits - Laboratory And Field Results
Authors: Feenstra R. , Walker B.H. 
Published: December 2007

A major effort has been made to evaluate the commercial application of bits fitted with STRATAPAX Drill Blanks for drilling oil wells. Over 40 field runs have been made with such Diamond Cutter bits and a significant potential economic application of the new material is indicated. Further development work will be required to improve bit design and manufacture as well as the wear and engineering characteristics of the diamond cutters.

Introduction

Surface-set diamond bits usually contain natural diamonds. The available, as-manufactured, Synthetic diamonds are too small to be used economically in these bits for oilfield drilling. A technique has, however, been developed by the General Electric Company to bind small synthetic diamonds together with a diamond-to-diamond bond on top of a tungsten-carbide substrate. As a result, a relatively large diamond cutter could be produced. The technique was initiated in the manufacture of diamond compacts for machining and dressing purposes. The product was named "COMPAX Industrial Diamond Blank". product was named "COMPAX Industrial Diamond Blank". With the success of this application, these diamond blanks were introduced into the drilling-bit industry. Recently a similar product, named STRATAPAX Drill Blank, was offered particularly for rock-drilling purposes. Mainly during the past few years several companies began to develop bits suitable for fitting with these diamond blanks for use in oil-well drilling. This paper reviews the results of a major effort obtained from over forty field runs with such bits, fitted with either COMPAX or STRATAPAX blanks. Such bits will be referred to as Diamond Cutter bits.

In addition, some general information on STRATAPAX Drill Blanks is discussed and results of a number of laboratory experiments are presented. Though a competitive product - SYNDITE is now also available, it has not been product - SYNDITE is now also available, it has not been included in the field tests reported here.

WHAT IS A 'STRATAPAX DRILL BLANK'?

Examples of a STRATAPAX Drill Blank are shown in Fig. 1. Each blank is made up of a thin diamond layer (minimum thickness 0.5 mm or 0.020 in), firmly bonded to a tungsten-carbide substrate. This layer is obtained by subjecting a mixture of small high-quality synthetic blocky diamond particles and a small amount of catalyst to very high pressures and temperatures. Because of the catalyst selected the diamond layer has only an effective operating-temperature limit of about 700 degrees C, beyond which level the bond between the individual diamond crystals loses its strength. This temperature limitation has proved to be a significant handicap in the development of the processes for attaching the STRATAPAX Drill Blanks to the processes for attaching the STRATAPAX Drill Blanks to the bit, because conventional diamond bit manufacturing methods use temperatures over 900 degrees C. This temperature limitation could also affect the wear of the cutting edge of the bit in actual operation.

The diamond layer features a polycrystalline structure without cleavage planes. This is only matched in nature by carbonado diamonds, which have only been used to a limited extent in drilling bits because of their short supply and high cost. The cost of STRATAPAX Drill Blanks is also high, but unlike the carbonado diamonds, the supply of diamond blanks is virtually unlimited.

The diamond blank exhibits the following important advantages over the types of natural diamonds generally used in bits for oilfield application:–a generally sharper cutting edge–higher-quality diamond crystals–a polycrystalline and crack-free structure.

These advantages only apply if the temperature limit for the diamond layer is not exceeded. Since this limit may be exceeded during the drilling operations, there is clearly a need for further improvement of the STRATAPAX Drill Blanks.

The diamond layer is firmly bonded to a tungsten-carbide substrate, which is about 2.7 mm thick.