PDC leaching

Background

Polycrystalline diamond compacts (PDC) have been used in industrial applications, including rock drilling applications and metal machining applications. Such compacts have demonstrated advantages over some other types of cutting elements, such as better wear resistance and impact resistance. The PDC can be formed by sintering individual diamond particles together under the high pressure and high temperature (HPHT) conditions, in the presence of a catalyst/solvent which promotes diamond-diamond bonding. Some examples of catalyst/solvents for sintered diamond compacts are cobalt, nickel, iron, and other Group VIII metals. PDCs usually have a diamond content greater than seventy percent by volume, with about eighty percent to about ninety-eight percent being typical.  PDC is bonded to a substrate, thereby forming a PDC cutter, which is typically insertable within, or mounted to, a downhole tool such as a drill bit or a reamer.

PDC leaching

PDC cutters are made by tungsten carbide substrate and diamond powder under high temperature and high pressure. Cobalt is a binder. Leaching process chemically removes the cobalt catalyst that includes a polycrystalline structure. The result is a diamond table with improved resistance to thermal degradation and abrasive wear, resulting in a longer useful cutter life. This process is normally finished in more than 10 hours under 500 to 600 degree by vacuum furnace. The purpose of leached is to enhance the toughness of the PDC. Normally just oil field PDC adopts this technology, because the working environment of oil field is more complex.

Brief History

In the 1980s, both GE Company (USA) and Sumitomo Company ( Japan) studied the removal of cobalt from the working surface of PDC teeth to improve the working performance of the teeth. But they did not achieve commercial success. A technology was later re-developed and patented by Hycalog（USA）. It was proved that if the metal material can be removed from the grain gap, the thermal stability of the PDC teeth will be greatly improved so that the bit can drill better in harder and more abrasive formations. This cobalt removal technology improves the wear resistance of PDC teeth in highly abrasive hard rock formations and further broadens the application range of PDC bits.