Abstract For the past few years the industry has been trying to extend the operating range of polycrystalline diamond compact (PDC) bits in terms of formations that can be drilled. Initially, the direction was uphole to the softer formations where the high standoff blade bits and large diameter PDC bits have proven economic. The next step is to extend downhole where the formations are harder and generate more heat. Typically, either tungsten carbide insert (TCI) bits or natural diamond bits are used in these harder formations because the heat degrades the polycrystalline diamond compact cutters. However, insert bits tend to be short-lived and require tripping more often than is satisfactory. and diamond bits have penetration rates that are slower than desirable.
Bits using PDC cutters with enhanced thermal stability and a radius of curvature on the diamond table have demonstrated a significant economic impact in many harder formations. The diamond wafer is shaped like a dome and set in the bit in place of the conventional, flat PDC cutters. The dome shape dissipates heat better, facilitates more efficient mechanical cuttings removal and drills with a constant rate of penetration throughout the life of the cutter due to the variable rake angle.
In addition to extensive laboratory testing, a rigorous field-test program was undertaken to determine the significance of this new program was undertaken to determine the significance of this new development. Field-test results are presented from Northern Europe and the lower Wilcox Frio sands and other formations of South Texas.
Introduction Since polycrystalline diamond compact drill bits began to drill successfully, the industry has speculated about the limits of this technology. The application window has widened from illitebased shales in oil-based mud systems to smectite shales in waterbased must systems. These developments were accomplished with flat PDC cutters, in 1/2-in. diameter and then in larger diameters.
End-users of PDC bits began to think in terms of their applications rather than in terms of the materials available on the market. In this way, the operators and contractors began to drive the development focus of the drill bit and diamond materials manufacturers.
The ultimate goal of the shaped-cutter development program was to enable a PDC bit to drill economically through a wider range of formations with greater reliability. Specifically, the synthetic diamond designers set out to:Create a geometry that maintained an effectively constant work rate throughout the working life of the cutter.
Create a larger diamond surface area for improved heat dissipation and for more effective thermal transfer to the drilling fluid.
Create a surface that would cut chips more effectively, thus providing more efficient cooling of the cutter.
Materials Development In 1981, work began to manufacture polycrystalline diamond on a curved tungsten carbide substrate for percussion bits and roller cone bits. Spalling problems occurred because the diamond layer has a much greater rigidity than the tungsten carbide. A new diamond layering technology was developed to solve the mismatch of materials properties. properties. A "transition" of properties from carbide to diamond was accomplished by mixing sintered carbide powders with diamond powders in various amounts. The layers of transition material adjacent to the carbide substrate have a high percentage of carbide powder, while the layers next to the full diamond layer have less (Figure 2). This patented technology allows the diamond parts to perform reliably patented technology allows the diamond parts to perform reliably under much higher impact levels.
This technology was then applied to shear-cutter technology. Prior to the development of transition layering, the ability to manufacture consistently reliable, curved shear cutters was extremely limited.