Role of cobalt of polycrystalline diamond compact (PDC) in drilling process

• Thermal stability of cobalt is largely affected by the frictional heat.
• The great difference in the thermal expansion of cobalt and diamond will cause microcrack under continuous impact.
• Oxidation of cobalt can be negligible during drilling process.
• Soil will increase the destruction risk of PDC from the continuous impact.

The contact surface between polycrystalline diamond compact (PDC) and rock was divided into three main areas according to the distinction in heat caused by various frictional forces during drilling process. As temperature rising during drilling, Co played a dominant role in the thermal stability of PDC, however the influence from Co oxidation could be negligible. Usually PDC has a self-sharpening ability with Co removing during drilling, while the injected cooling water (generally mixtures consisting of water and soil) breaks the formed shape. That is because water molecules and soil adhere to the frictional surface thereby forming an absorbed film which prevents direct contact between PDC and rocks, thus the effect from continuous impact forces is enhanced which brings about more unfavorable results. Controlling the content of Co is not only a vital problem existing in PDC industry but an effective way to improve drilling performance.

Heat and forces distribution zones on cutting edge of PDC generated in drilling process.Figure optionsDownload as PowerPoint slide