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Hybrid drill bit combines speed of PDC bits with toughness of tricones
As far back as the early 1900s, when the rudimentary fishtail drill bit was superseded by the roller cone bit—a marvel of engineering that was to revolutionize the oil industry—the limitations of the technology were well-known.
The two-cone bit introduced by Howard Hughes Sr. and Walter Sharp in 1909—to become the three-cone, or trademark tricone, bit in the 1930s—proved ideal for boring through medium- and hard-rock lithology. But in soft or plastically behaving formations like shale, roller cone bits lacked the performance and speed of fixed cutter bits such as today’s polycrystalline diamond compact (PDC) bits.
Conversely, while the continuous shearing and scraping action of fixed-blade bits may be superior in malleable formations, they are prone to breakdown when encountering hard rock such as abrasive sandstone and cement stringers, where roller cones excel. Unfortunately, many wells penetrate both, alternating hard-soft-hard, making the choice of one or the other drill bit a compromise.
At least until now. After years of research and testing, Baker Hughes Incorporated—the company that traces its roots to Hughes’ roller cone invention—introduced a hybrid drill bit in 2011 that synthesizes the best attributes of each. Its Hughes Christensen Kymera bit (named for chimera, a mythological creature with disparate parts derived from two or more animals) incorporates two to three roller cones—equipped with tungsten carbide inserts—and three or four arms of PDC cutters in a single unit, bringing together the rock-crushing strength and stability of a roller cone bit with the continuous shearing action and superior cutting of the PDC bit.
Combined, the two technologies create smoother drilling, improved torque management and precise steering capabilities, says Clair Holley, vice-president of wellbore construction, resulting in faster, more-consistent drilling than either roller cone or PDC can provide alone. “We believe the applications are widespread and anticipate continued growth with the entire Kymera offering as customers see the advantages of this hybrid bit,” Holley says.
In either motor or rotary drilling applications, and on a variety of bottomhole assemblies, the hybrid Kymera bit has boosted drilling rates up to 62 per cent and extended single-bit run lengths more than 200 per cent in the United States. In applications in interbedded formations in western Canada, the bit has performed 60–100 per cent faster than competing bits.
NuVista Energy Ltd. was the first to use the bit in Canada. Drilling the build sections (turning from vertical to horizontal) of wells in the Wapiti Montney area in Alberta’s Deep Basin, a liquids-rich natural gas play, the company estimates savings of $200,000 per well using the Kymera.
Seeking the steerability and reliability of a roller cone bit and the penetration of a PDC bit, NuVista first tried the Kymera last January, says Mark Thorne, NuVista drilling superintendent. The tough interbedded formations typically claim about four roller cone bits per well, meaning four time-consuming bit changes, or trips, per well. NuVista trimmed that to two trips using the Kymera, and given the experience of other operators in the area that have also switched to the Kymera, Thorne says that will likely drop to one trip per well.
“It has been proven to us and to other operators who are now using it that it is the fastest and most economic way to drill the build section,” Thorne says. “In interbedded formations, or basically just hard rock, it’s a real great application. We have used it on every well since [January], and our go-forward plan is to continue to use it on every Montney horizontal well that we drill.”