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While significant advancements have been made in the field of Polycrystalline Diamond Compact (PDC) cutter technology over the years, understanding of the thermal fracturing behavior of these cutters is still limited. Traditionally, analysis of thermal fracturing was conducted by heating the cutter to the fracture point in normal atmospheric or vacuum/inert conditions, and then allowing it to cool down and polishing it for easy observation prior to microscopic analysis. This method limits findings, as the environmental conditions do not accurately reflect those experienced downhole, and this process does not allow for an in-depth understanding of the precise fracturing behavior of the cutter. To gain a more in depth understanding of thermal fracturing behavior and its causes, a specialized environment was prepared that allowed in-situ observations of fracturing behavior in simulated drilling conditions. This included equipping a Scanning Electron Microscope (SEM) with a heating-stage furnace accessory to allow for real-time observations and filling the chamber with a simulated atmosphere consistent with downhole conditions. Cutter cross-sections were selected and polished using new methods to ensure maximum clarity and then heated to fracturing temperatures, with the SEM recording all changes as they occurred. The observed thermal fracturing behavior, analysis of the microstructure degradation and EDS chemical analysis led to some valuable insights into cutter failure mechanisms. In the unleached areas of the cutters, fracturing began at significantly higher temperatures than expected, while the cobalt binder compound began melting at lower temperatures than commonly accepted. In addition, fracturing behavior was not universal, but began with a few major cracks appearing in the PDC structure, from which a network of smaller cracks progressed outwards through the cutter. With deep leached cutters, microcracking appeared in the diamond grains rather than intergranular fracturing, degrading the integrity of the cutter and indicating that graphitization, not fracturing, is the primary thermal failure mechanism of these cutters. The data from these tests provides valuable insights into how PDC cutter and deep leach technology can be effectively used in the field. Due to the lower melting point of the cobalt binder compound, the temperatures used in manufacturing can be adjusted to ensure maximum cutter stability. In addition, these tests demonstrate a greater-than-expected wear resistance for deep leach cutters and a higher fracturing or degradation temperature of both unleached and deep leached cutters, meaning that they are suitable for a wider range of applications. |
