Multi-functional design gives new life to impregnated diamond bits

Impregnated bit patents date back to the 1800s. These bits originated in the mining business, drilling predominantly short sequences and one rock type. As a result, bit design was relatively easy and followed a simple concept - use one of the hardest materials on earth to increase bit drilling capability.

The oil and gas industry recognized the potential of this technology for specific drilling applications. Drilling longer sequences of homogeneous, competent formations created a need for a durable bit with extended longevity characteristics. The same simple concept was used, and the impregnated diamond bit was the result. Performance was as expected, with the bit drilling harder, more competent rock very effectively, and softer rocks not drilling efficiently at all.

In many situations, long homogeneous sequences are not the norm, and drilling multiple formation types and sequential formation changes occur. Many formations with very diverse drilling strengths can be encountered over the length of a well, exceeding the operating limits of impregnated diamond bits. Intermittent low rates of penetration and erratic bit torques are often experienced.

This bit is designed to expose a fresh, traditional diamond bit, cutting surface after drilling completion equipment.

All-purpose bit

The use of steerable motors and the development of polycrystalline diamond compact (PDC) bits and PDC-drillable completion equipment reduced demand for impregnated diamond bits in the recent past. Expanding drilling operations around the world, however, has generated a need for a bit capable of drilling more competent formations and completion equipment within the same bit run.

Hycalog, a Schlumberger Company, recognized this need and developed an alternative for use in these environments. The TSP Enhanced DuraDiamondtrademark Bit has been developed to aggressively drill completion equipment and then continue drilling through harder geologic rock sequences.

This Hycalog 300 series bit design is based on the 440 series. The distinguished sharp nose and tapered shoulder are still prominent in the overall bit look. The difference in the series' is in the thermally stable polycrystalline (TSP) disks impregnated in the tungsten carbide matrix with the smaller diamond inserts. The 10 mm TSP disks are imbedded 6 mm within the carbide matrix, leaving a 4 mm cutting area for each disk. These diamond disks are comparable in size to cutters in some PDC bit designs currently used today.

The 6 mm embedded disk depth gives more mechanical retention strength for the diamond disks, reducing the chance of a lost disk while drilling completion equipment. Impact damage is still a problem for diamond bits, but, drastically reducing the chance of a lost tooth prolongs the life-cycle of a given bit.

An example of TSP disk durability was illustrated with rig test of a 5 7/8-in. TSP enhanced impregnated bit, run on a turbine, to drill out two sets of float equipment and stage tool. At a depth of 1,015 ft, the following drilling parameters resulted in 50% wear on nose cutters and 20% wear on all remaining cutters:

• WOB - 2,000-4,000 lb
• RPM - 1,400 maximum, with turbine
• GPM - 200
• Drilling fluid - water.

Field testing of these new diamond bits has continually showed rates of penetration comparable to rock bits, while drilling completion equipment and formation. Tests have indicated that directional response is not affected greatly. The bits have been tested on turbines and rotary assemblies. All information indicates that steerable motors and turbine systems should be compatible with these bits.

References:

Tristan, S., Macmillan, R., Caraway, D., Brown, G., Energy Sources Technology Conference & Exhibition; Paper ETCE99-6647.

Acknowledgements:

D. Caraway and B. Miller of Hycalog provided information for this article.

Weatherford and Neyrfor assisted Hycalog in bit rig testing.