[Editor's note: This story originally appeared in the January 2020 edition of E&P. Subscribe to the magazine here.] 

The drilling market is continuously evolving, but one thing that has been made clear in recent months is that capital efficiency and constraint within the drilling industry will be a focus for the foreseeable future.

Operators must turn to new solutions to reduce spend and achieve greater profitability in well programs. National Oilwell Varco (NOV) has released the Vector Series 50 SelectShift downhole adjustable motor to its portfolio of downhole tools and technologies. The low-risk, all-mechanical drilling tool addresses the economic and performance-related needs of this changing market.

The SelectShift downhole adjustable motor provides operators with the flexibility to shift between the straight and bent position downhole. This capability, combined with the motor’s higher torque output and 100% flow to the drillbit, allows the SelectShift to outperform traditional motors, eliminate trips and improve drilling efficiencies. The SelectShift downhole adjustable motor combines the power and reliability of a drilling motor with greater operational flexibility. This all-mechanical design offers bend setting options similar to those of traditional motors.

The driller shifts the bend angle of the motor downhole between a high-bend or straight/ low-bend position within a couple of minutes via adjustment to flow rate and rotary rpm. A permanent standpipe pressure signal difference, ranging from 150 psi to 250 psi, is seen on the surface indicating the position for bend setting confirmation. There is no restriction on the number of downhole shifts between the high-bend and straight/low bend positions and vice versa that the driller can make.

Internally, the universal joints include torque-transferring faces versus the traditional ball and socket arrangement. This feature enables the motor to provide exceptional torque capability and reliability. In addition, the SelectShift downhole adjustable motor incorporates the latest oil-lubricated bearing assembly technology, which maintains a similar bit-to-bend length as a conventional drilling motor even with the added technology of the bend angle shifting mechanism.

NOV’s SelectShift downhole adjustable motor has the capability to shift between the straight and bent position downhole. (Source: NOV)

Field trials
Field-testing was initiated in 2018 as part of a comprehensive technology validation program. The earliest testing was coordinated at NOV’s live test rig in Navasota, Texas, and at the Catoosa Test Facility in Jennings, Okla. Thereafter, field trials with operators in the Bakken, Permian, Eagle Ford and Midcontinent were undertaken with vertical/tangent/nudge sections a primary focus. Several runs in curve, curve/lateral and lateral sections also were initiated. Through these trials, several key objectives were set and accomplished:
• Successfully shifted bend angle downhole, proved tool function and permanent standpipe pressure signal difference on surface;
• Successfully optimized shifting procedure to reduce nonproductive time;
• Reduced motor stab outer diameter to mitigate surface torque; and
• Determined compatibility of tool and MWD operations.

To date, more than 130,000 ft have been drilled with the SelectShift downhole adjustable motor, with more than 370 straight or low-bend shifts downhole. Though most runs were in the vertical/tangent section, the SelectShift most recently drilled a 12,985-ft lateral in the Permian Basin.

Case histories
An operator in the Permian Basin needed to drill an entire 8¾-in. vertical/tangent section to the kickoff point (KOP) while effectively holding inclination and improving bit life. The section consisted of a challenging lithology of sandstones, siltstones and limestones, and harsh downhole conditions had previously been encountered. On offset wells, the operator had to pull the bit due to bit damage before reaching the KOP. On this run, ensuring that the bit reached total depth with an optimal bit dull was of critical importance.

The Vector Series 50 SelectShift downhole adjustable motor was chosen by the operator to address the challenge of multirun trips to the KOP. The motor was configured with an 8½-in. stabilizer and a 7-in. 7⁄8 lobe, 5.7-stage even rubber thickness power section and was paired with a seven-blade, 19-mm cutter PDC drillbit. The SelectShift downhole adjustable motor was configured to operate between 1.83 degrees and 0 degree bend settings. The system successfully reached the KOP in one run, drilling 2,719 ft with the SelectShift in the 0-degree setting. In addition, hole inclination was easier to hold with the tool in straight mode, which reduced the number of slides by 57% versus the offset well. The bit was deemed repairable, and with a bit dull of 1-3-BT-S-X-I-CT-KOP, it was in significantly better condition than the previous bit.

Other projects have displayed additional benefits from using the SelectShift downhole adjustable motor, with drilling optimization as a potential area for greater development. In one instance, using the SelectShift tool resulted in an increase in rotary rpm by 40% with a decrease in surface torque by 20% and weight on bit by 8%. As torque decreased, a concurrent increase in ROP was observed with improvements up to 54% when compared to being in bent position versus the straight position on back-to-back stands.

Another area where the SelectShift tool is demonstrating its potential is in reducing slide percentages. The key in this functional domain is that operators using the technology gain experience operating the tool in the field, which will lead to achieving the maximum performance benefit. In one project, an operator started out drilling 9.9 sliding hours, a total of 30% across a 6,238-ft interval. By the time it had reached the third well and gained more experience using the tool, sliding hours had been reduced to 3.8 hours, a total of only 12% across a similar 6,175-ft interval. Continued use of the SelectShift enabled this gain in drilling efficiency in the vertical/tangent section.

Moving forward
NOV’s approach to accelerating development of the SelectShift technology and performance evaluation has been by a combination of internal tests and customer field trials. After initially focusing on validating the concept, the company moved to minimize shift times and shift procedure optimization downhole. Now, the primary focus is on optimizing drilling parameters, enhancing ROP and eliminating trips.

The current state of drilling, particularly in North America, will lead to increased technology adoption. Pad drilling with batch wells is a perfect example of an application where the iterative cycle of learning with the SelectShift can benefit the operating company, especially in the vertical/tangent section. On the first run, drillers can get a feel for running a new tool, acclimating themselves to the shifting mechanism. On the second run, parameters can be adjusted to improve downhole drilling dynamics as familiarity with the tool increases. By the third run, the driller can focus on improving ROP and eliminating trips, thereby reducing drilling costs. This cycle is part of a process of scaling the technology across rig fleets.

New drilling technologies will continue to be important as oil and gas companies seek efficiency gains and better returns on capital deployed. When choosing their solution, companies would be wise to find an answer that balances cost with proven performance.