Unique Hybrid Drill Bit with Novel PDC Cutters Improves Performance in Ultra-Deepwater Brazil Pre-Salt Application

Abstract

The Brazil ultra-deepwater, pre-salt application has been a very challenging drilling environment since exploration activity began in 2005. The initial pre-salt section contains limestone with random silicified nodules. Over the last few years, operators have collected large amounts of data for service companies to analyze to improve drilling performance through bit design. Using this information, a hybrid bit design with the most advanced cutter and bit technology was developed successfully increasing the distance drilled by 138% and the rate of penetration (ROP) by 171%. Prior to advanced hybrid bit technology, a variety of other drill bit technologies such as polycrystalline diamond compact (PDC) bits and impregnated designs were used in the pre-salt. Historically, impregnated bits had longer runs, but with high mechanical specific energy (MSE) and low ROP, drilling with these bits was not economical. Contrarily, PDC bits can deliver higher ROP but cannot drill as far as impregnated bits. Three hybrid designs, the last one using dual-chamfer technology, were brought into this application to reduce cost-per-meter through better drilling efficiency and ROP. Each successive design managed to exceed customer expectations. Extensive laboratory tests were conducted on the hybrid designs to address the demanding needs of pre-salt applications. These unique bits showed promising results on atmospheric surface rig tests and in pressurized bottomhole simulator testing. Hybrid bits produced much less torque, with smoother torque fluctuations and faster ROPs than roller-cone and PDC bits through the simulated interbedded formations in laboratory testing. Novel dual-chamfer cutters used in the bit have been lab tested on a vertical turret lathe (VTL), a visual pressurized single-point-cutter (VSPC) test machine and a monotonic loading test. Cutter testing showed positive VTL results and increased resistance to diamond fractures. Ultra-deepwater drilling is very demanding and expensive, so operators want to achieve total depth in just one run by avoiding trips to change out the bit or bottomhole assembly (BHA). The improved bit and cutter technology resulted in significant cost savings and confidence for the customer. The performance of the hybrid bit with dual-chamfer cutters was significantly better than offsets, saving the operator approximately USD 9769/m.