What type of drill bit is best suited for formations with high compressive strength and low abrasivity, and what parameters influence it?

For formations with high compressive strength and low abrasivity, a Polycrystalline Diamond Compact (PDC) bit is generally the best choice. PDC bits use fixed cutters made of synthetic diamonds bonded to a tungsten carbide substrate. These cutters shear the rock formation as the bit rotates, making them very effective in hard, non-abrasive formations. Unlike roller cone bits that crush the rock, PDC bits rely on a continuous shearing action, which is more efficient in formations that resist indentation but can be cleanly cut. Several parameters influence the performance of a PDC bit in these formations. Weight on bit (WOB) is a critical parameter. A sufficient WOB is necessary to engage the cutters and initiate the shearing process. However, excessive WOB can damage the cutters or lead to bit whirl, which reduces drilling efficiency and bit life. Rotary speed (RPM) is another important parameter. Higher RPMs generally increase the rate of penetration (ROP) in hard formations, but the optimal RPM must be balanced against the risk of overheating the cutters. Cutter size and geometry also influence performance. Smaller cutters with a more aggressive profile are generally more effective in hard formations, as they can generate higher stresses at the cutting interface. The hydraulic horsepower (HHP) available at the bit is also important. Sufficient HHP is needed to clean the cuttings away from the bit face and prevent them from interfering with the cutting process. In summary, selecting the right PDC bit for formations with high compressive strength and low abrasivity requires careful consideration of WOB, RPM, cutter design, and hydraulics to optimize drilling performance and bit life.