Fabrication And Laboratory Testing Of A Bit Containing Diamond Compacts
Authors: Daniels W.H. , Thompson D.A. 
Published: December 2007

The General Electric Company recently introduced a series of cutting elements called STRATAPAX drill blanks for oil and gas well drilling. These drill blanks consist of a manufactured polycrystalline diamond layer on a tungsten carbide substrate. These blanks have been successfully used in drilling soft to medium hard formations where they exhibited a combination of high impact strength and abrasion resistance. Several different bit designs have been developed employing the STRATAPAX drill blanks. This paper describes the fabrication and lab testing of one specific design developed by General Electric Specialty Materials Department for field evaluation of the STRATAPAX drill blanks.

In the bit fabrication a combination of furnace brazing and induction brazing was employed to attach the STRATAPAX drill blanks to the bit face. Details of this operation and some of the specific problems encountered will be described. As a result of this fabrication process some limitations in the use of STRATAPAX drill blanks in oil bits have been overcome.

Details of the laboratory tests of this specific bit are presented in the paper. Included in this data is drilling performance obtained as a result of tests using a series of bit weights and rotating speeds in both Carthage Marble and Sierra White Granite. Following successful laboratory testing, the bit was field tested in the U.S.

Introduction

To meet the needs of the industry for a more efficient way to drill oil and gas wells, General Electric recently introduced STRATAPAX drill blanks which consist of a sintered diamond layer on a tungsten carbide substrate. These drill blanks are designed specifically for rock cutting. They exhibit a desirable combination of high impact strength and abrasion resistance suitable for improving drilling performance in several types of formations. Since the commercial introduction of STRATAPAX drill blanks in December, 1976, several designs have been developed by bit fabricators to incorporate the blanks into a drilling system.

Early work by General Electric in the development of these cutters for rock drilling yielded a bit configuration using the STRATAPAX blanks brazed to cemented tungsten carbide slugs. The initial laboratory drilling and field testing results of these bits were reported in 1974. Since that time, additional modifications in the slug type bit design and improvement of the physical properties of the drill blank have been achieved. This paper describes the design and fabrication of the current slug bit along with laboratory test performance.

DESIGN CONCEPTS

The basic slug type bit containing STRATAPAX drill blanks is shown in Figure 1. Each cutting element consists of a STRATAPAX blank bonded to a cobalt cemented tungsten carbide support slug depicted in Figure 2. These slug/STRATAPAX blank subassemblies have been fabricated individually by an induction brazing process and subsequently interference fit into a machined steel bit body. The steel bodies were machined from AISI 4340 steel hardened and drawn to Rc 40–46. The earlier bits had a negative 5 deg. rake on the cutting element and a 5 deg. relief on the carbide slug.

Experimental investigations of the mechanical performance of individual slug-drill blank units revealed performance of individual slug-drill blank units revealed that improved rock cutting performance can be achieved with a larger negative rake (-15 deg.) of the cutting edge and more relief on the carbide. These larger back rakes with the associated relief present difficulties in conventional interference fitting operations. In addition, it appeared that improvements in the nozzle retention system and erosion resistance of the bit body would improve bit performance. It was desirable, therefore, to develop an alternative fabrication approach. The technique selected employed an infiltrated hard matrix bit body to which tungsten carbide slugs were attached by furnace brazing. The STRATAPAX drill blanks were subsequently bonded to the slugs by induction brazing.