Design Of Special Performance Bits Utilizing Synthetic Diamond Cutters
Authors: Huff Charles F. , McFall Alan L. , St. Clair Jack A. 
Published: December 2007

Abstract
A new technique (diffusion bonding) for attaching synthetic, polycrystalline diamond cutters to drill bits has been developed by Sandia Laboratories with funding from the Department of Energy. To test the diffusion bonding technique and some new bit design concepts, Sandia is designing several types of special performance bits utilizing synthetic diamond compacts. Two all-compact bits, a hybrid diamond-compact/roller-cone bit, and two coring bits are being built for testing in laboratory and field environments. A special coring bit designed to operate with a pressure coring system and to be cleaned and cooled with a small quantity of low-invasion coring fluid is undergoing drilling tests. One configuration of the downhole replaceable chain drill utilizes synthetic diamond cutters at the pivot point, while a second configuration utilizes these cutters exclusively. This paper describes the design of each bit and paper describes the design of each bit and presents the results of recent drilling tests. presents the results of recent drilling tests. Design and testing philosophy are reviewed and plans for future design revisions and testing plans for future design revisions and testing are described.

Introduction
It is generally accepted that synthetic diamond compacts hold significant promise as cutters for bits used in drilling rock. These compacts consist of a layer of synthetic poly-crystalline diamond grown on a poly-crystalline diamond grown on a tungsten-carbide substrate. Many previous attempts to utilize these cutters on bits had been unsuccessful because the method used for bonding the cutters to the bit did not provide adequate bond strength. In 1975, Sandia initiated a program to develop an improved bonding program to develop an improved bonding technique. A diffusion bonding technique has been developed, and to test the efficiency of the bond, laboratory and field tests of bits utilizing the bond are required. In addition, interest has arisen in several projects where bits with special performance characteristics are required. Extensive analysis and experiments led to the conclusion that synthetic diamond compacts had capabilities that would make them effective in the bits designed for these projects.
As a result of these needs, Sandia Laboratories embarked on several projects to design and fabricate special performance drill bits. These bits are being designed to support programs where unusual bit designs are required. Each of these bits has in common the use of synthetic diamond compacts as cutting elements in some portion of the bit. The particular compact utilized to date for these bits is the General Electric Company product, Stratapax, because of the availability of the product and the extensive testing conducted on it. The projects are all supported by the Department of Energy.
Full-faced diamond compact bits are being fabricated in 4-3/4 and 6-1/2 inch diameter sizes to test the diffusion bonding attachment technique. A hybrid diamond-compact/roller-cone bit is also being built. Compacts are used here to cut the outer portion of the hole and the roller cone is portion of the hole and the roller cone is used to limit the penetration of the bit as it drills.
The downhole replaceable, continuous chain bit utilizes compact cutters mounted on the links of the chain. This cutting structure has been tested with excellent results.
Several core bits are also being built.