Motors are failing, transmissions are cracking, power sections have blown out and other catastrophic failures have occurred somewhere along the drillstring in recent history. Situations that drilling engineers haven’t worried about have started to become a common occurrence due to the extreme changes in drilling programs. A normal positive displacement motor from three years ago averaged a maximum torque output anywhere from 4,000 ft/lb to 6,500 ft/lb. That’s a light load when compared to motors in West Texas today seeing a maximum torque output of greater than 20,000 ft/ lb. This trend isn’t isolated to West Texas as Midcontinent applications in the SCOOP and STACK have seen weight on bit (WOB) go from a norm of 15,000 lb to 30,000 lb to almost 100,000 lb. This change to extreme parameters has emerged steadily over the course of the last couple of years without bits taking those same necessary precautions.
Operators have reason to do this as nearly all applications where this strategy has been applied have seen gains in their ROP, resulting in reduced cost. During the course of these failures nearly every component of the bottomhole assembly (BHA) has been reengineered and bolstered to keep pace with the demands and changes to the drilling environment—except the drillbit.
Over the past year Ulterra has looked critically at bit design, blade geometry, cutter reinforcement and hydraulics and has been testing new materials, which has resulted in its XtremeParameter (XP) line of polycrystalline diamond compact (PDC) bits. With the increased energy going through the bit, it is Ulterra’s goal to make sure the bits do not become the limiting factor in performance.
“We’ve seen more and more operators move toward higher WOB and higher torque motors,” said Shane Campbell, manager for Ulterra’s Permian District. “Operators are now asking more out of their BHAs and our bits than ever [before].”
“For the operator pursuing high WOB and torque, advances and research into materials and blade and bit geometry should ensure that nothing comes between drilling engineers and reaching TD [total depth] as fast as possible,” said Aron Deen, director of technology and strategic marketing for Ulterra.
Some of the most defining characteristics of a PDC bit—body design and blade geometry—have been reengineered to not only withstand the immense pressures but harness those forces into the formation. Instead of viewing the bit body and blades as separate entities in the design process, Ulterra has taken the approach of “growing” the blades out of the body. As these forces keep increasing, damage gets exacerbated quickly through the drillstring. The blade’s ability to capture and disperse that energy must be amplified for the cutters to efficiently use the WOB and torque. Over the course of a yearlong research and implementation program the company determined a new way for those blades to be built. Finite element analysis showed that blade strength nearly doubled by using this new design process.
In the design of a drillbit engineers chase diverging results in durability and performance. Ulterra has strengthened the bit body and blades while simultaneously keeping the efficient cutting structure, making sure performance isn’t sacrificed at the expense of durability. In recent field tests of this technology the XP bit demonstrated dramatically reduced bit body damage and helped an operator in New Mexico set a new run record in its 8.75-in. interval.
With the results attributed to the extreme drilling parameters the propensity of higher drilling parameters doesn’t seem to have an end in sight. Ulterra has tried to jump ahead of these aggressive operators by looking analytically at its cutter management system. By managing its cutters in a new way, the company takes into consideration the location of the cutters and their particular function. Engineering then caters each cutter specifically for the purpose that it performs downhole, whether that be for abrasion, impact, depth of cut control or any other cutter requirement.
This new tailored way of cutter management has been coupled with the addition of structures to the primary cutting surface to help better convey the energy through the bit and help fail the formation. Ulterra fortified the secondary features like load limiters and backup cutters. These fortifications help with the steerability and toolface control that directional drillers are chasing while minimizing the risks to durability that adding these features can cause.
Operators are pushing toward longer gauge bits. With the immense pressures exerted downhole coupled with the longer gauges, there are numerous concerns to be had along the drillstring, including bit whirl and stick/slip. Stick/slip at the drillbit is initiated due to inconsistent torsional requirements at the drillbit/rock interface. When stick/slip happens, the drillbit reacts violently against the formation, resulting in damaged cutters and blades. With the XP drillbit the company released different features along the gauge pad to help alleviate those concerns. Releasing a proven chamfer along the gauge pad will help the bit slide along the borehole as opposed to a sharp gauge pad, which tends to grab the formation. In part, longer gauge pads help to dampen drilling vibration. The company coupled XP bits with the power of its patented CounterForce technology to redirect vibrational energy into more efficient drilling.
“We have kept the majority of the development and testing under the radar until it had been perfected,” Deen said. “The truth, though, is that many of the gains have been realized in our products over the last 12 months. In field tests these innovations have shown to more than double the strength of the blade and improve the integrity of the cutter pocket. Field results allowed for a Q2 official launch of the XP line.”