NOV’s understanding of thermal mechanisms leading to their patented deep leach technology has provided a significant breakthrough to the drilling industry by extending the boundaries of fixed cutter bit designs. Although thermal degradation is still the primary mode of polycrystalline diamond compact (PDC) failure, the varied nature of the drilling industry means that failure mechanisms such as thermal degradation, mechanical abrasion, cutter impact and mechanical overload vary depending on the specific application.
The emphasis of this technology is on reducing costs by drilling faster and ensuring greater durability through abrasive sandstone or tough limestone while maintaining the well path. Each application comes with its own unique challenges, such as maintaining steerability, stability, durability and rate of penetration (ROP). The combination of drill bit design and PDC cutter technology affects all of these, though performance is limited when cutters suffer from overload or thermal degradation.
The challenge is to identify the true failure mechanisms of the bit and cutter rock interaction, which can only be understood by a dedicated and highly focused team. What may work well in an application with a primary failure mode of thermal abrasion may not work so well in an application that suffers from impact damage.
NOV’s ReedHycalog™ Helios™ Inferno™ PDC cutters are precisely engineered to provide increased performance in specific applications. The primary goal in developing the Inferno cutter range was to define the principal failure criteria for each application and engineer a cutter with the precise properties to overcome these, to improve performance under these conditions. By understanding the exact failure mechanisms of different applications and formation types, NOV has created the Cutter Index, which allows the ideal cutter variant to be selected for the particular conditions.
The Cutter Index ranks cutter technology according to its resistance to the three primary failure mechanisms for most applications: thermal degradation, abrasion, and impact damage. Until recently, drill bit providers have sought to create the best overall cutter by balancing these resistances, with the expectation that their cutters would perform as well in one application as the next. Although the industry attempts to create a single optimal cutter, in many cases enhancing certain characteristics at the expense of others will provide the ideal cutter for the application.
Figure 1. Helios Inferno Technology is certified with a new Cutter Index that provides a ranking system to ensure the optimal cutter for the application.
This unique Cutter Index system ensures that the characteristics of each cutter used are ideally matched to the needs of the application. The development of the Cutter Index precipitated the development of the highly specialised range of Inferno cutters, allowing both customers and experienced field engineers to match the right cutter to the right application.
One example is an 8 ¾ in. six-bladed design that was able to drill two consecutive single-run vertical wells averaging more than 8000 ft. The failure mechanisms were identified as both thermal and abrasive, and using the Cutter Index, the cutter properties were matched to the application. This provided a 22% increase in the distance drilled while maintaining all directional objectives.
Williston Basin, North America
Figure 2. Williston Basin: Before 8 ¾ in. DS616M-X3, previous cutter technology. In: 2051 ft; Out: 7206 ft; Drilled: 5155 ft; Hours: 24; ROP: 215 ft.
Figure 3. Williston Basin: After 8 ¾ in. DS616M-X3-Z, Helios Inferno cutters. In: 2442 ft; Out: 7754 ft; Drilled: 5312 ft; Hours: 21.4; ROP: 248.2 ft.
The photos above illustrate two identical 8 ¾ in. DS616M-X3 bit designs used by the same operator in identical vertical intermediate sections. The section consisted of shale, sandstone, limestone, dolomite, and salt members with a wide range of thicknesses and compressive strengths. The only change was to incorporate the Helios Inferno cutters once the failure mechanisms had been identified.
The photos clearly show how matching the correct cutter characteristics to the application can yield a remarkable improvement in ROP and leave the bit with an excellent dull condition and very little wear. The use of specialised Inferno cutters allows the selection of the precise characteristics for the target operations, increasing bit performance. This permits operators to drill further and faster, resulting in significant cost savings.
Following their successful launch in the US market earlier this year, the Helios Inferno cutter range has been expanded through the development of many new variants. These new variants are better suited to specific applications, providing a greater range of options for global use.
Mabrouk Field, Oman
In Oman, two 8 3/8 in. SK616 bits equipped with Helios Inferno cutter technology were used to drill a vertical section through the Al Khalata, Hasirah, Saih Nihyda, Ghudun, Lower Ghudun and Al Bashair formations. In particular, the Al Khalata is well known in the area as being very difficult to drill. The formations vary from primarily sandstone sections with minor shale streaks to an abrasive sandstone/siltstone section interbedded with hard shale. A highly focused team was able to pinpoint the major failure mechanisms of previous runs and quickly identify the cutter characteristics necessary to provide a breakthrough in performance. This resulted in a new interval field record, including the longest 8 3/8 in. interval drilled in Al Khalata. Both SK616s were equipped with Helios Inferno cutters and successfully drilled through the entire interval, providing a higher ROP for the section and demonstrating superior durability with their exceptional dull condition.
Figure 4. First bit drilled 890 m, new field record including 260 m of Al Khalata.
Figure 5. Second bit drilled 645 m, Ghudun, Barakat, Mabrouk, Barik, Al Bashair and Miqrat.
Another important point regarding this field record is that previous footage records were only achieved with heavier set designs that had seven or eight blades. By focusing on the true failure mechanisms of the operation, the team was able to prove that improvements in cutter technology can yield breakthrough performance and in this case allow for a lighter set six-bladed design.
Solan Field, North Sea
In the North Sea, a 12 ¼ in. SK616M bit with Helios Inferno cutters surpassed performance expectations by drilling a very challenging Calcarenite section in the Solan field. The goal was to drill the 12 ¼ in. section to a planned intermediate section and TD below the Calcarenite member while meeting all directional objectives in a long radius development well.
The 12 ¼ in. SK616M was equipped with Helios Inferno cutters and run on an RSS tool with an NOV Anderreamer borehole enlargement tool (12 ¼ x 13 ½ in.). The job required building inclination from 0° to 65°. The formations encountered were mudstone, shale, sandstone and the challenging Calcarenite member. The Calcarenite contains particularly hard and abrasive layers, which have consistently produced, wear flats on all previous PDC bits run on these wells.
The bit achieved an interval of 4126 ft reaching the planned intermediate section to TD below the Calcarenite without issue. The SK616M provided consistent ROP throughout the section, but most particularly through the Calcarenite, resulting in a 188% increase in interval drilled compared with best competitor run.
The ability of Helios Inferno cutters to resist abrasion allowed the Calcarenite to be drilled with relatively low WOB, minimising side loading and resultant stabiliser wear. No other 12 ¼ in. bit has ever managed to drill the Calcarenite member without it being pulled early due to low ROP. Overall, the bit drilled 45% further into the Calcarenite than the nearest competitor while meeting all directional objectives.
Figure 6. Close up of 12 ¼ in. SK616M clearly illustrating the excellent dull condition of Helios Inferno cutters.
Helios Inferno cutters are quickly becoming the cutter of choice in many applications, as positive word of mouth has led to many operators demanding this new range of cutters for their operations. Although the Helios cutter is still preferred in the majority of applications, the Helios Inferno cutter provides increased performance in target applications, both in terms of durability and rate of penetration.
Read the article online at: https://www.hydrocarbonengineering.com/special-reports/02122014/nov-shares-helios-inferno-pdc-cutter-success-stories-from-around-the-globe/