Since 1859 when the first drilling rig was successfully used to drill the 69-ft-deep Drake oil well, the drilling industry has demanded and driven continuous improvement. Technology developments enabled ever-deeper drilling into reservoirs with myriad formations, temperature and technical challenges before the unconventional boom in the early 2010s turned the spotlight on horizontal drilling.

With the technology framework for developing an unconventional play established, the focus quickly shifted to reducing costs. Steep production decline curves necessitated replacement wells to replace lost production on an unprecedented scale. The need for cost reduction to make a play economic was exacerbated by the steep decline in oil prices in 2015.

Because unconventional wells are always directionally drilled horizontal wells, the downhole motor has a large impact on the ultimate performance when drilling the well. This is true for both conventional and rotary steerable applications. In conventional applications, the downhole motor is both the deflection device and the power provider to the bit. As lateral sections have become increasingly longer, the motor-powered rotary steerable bottomhole assembly (BHA) is the best methodology to achieve the length as well as to deliver the performance.

Positive-displacement downhole motors and their fundamental principles have changed little since their introduction in the 1970s. The rotor-stator configurations have evolved some to provide a range of torque, horsepower and rpm.

The push for increased motor performance has largely centered on the configuration of the power section. High rotor-stator configurations combined with longer power sections can deliver very high torque and horsepower ratings. The downside is reduced reliability due to failure of other components, often beyond the motor.

The high power also generates high vibration that can limit bit performance but, more importantly, cause premature failures of MWD tools. Therefore, even if the motor could continue, the BHA needs to be pulled because of MWD failure. The result is that performance gains and cost reduction are mitigated by inconsistent execution.

Baker Hughes’ Navi-Drill Ultra and Navi-Drill X-treme series downhole motors have continued to push the performance boundary since their introduction in 1995 and 2002, respectively. But taking the next step in motor performance would require a complete redesign from the ground up.

Building a better motor

Baker Hughes began the motor redesign by conducting a detailed application study and review of unconventional wells drilled in the previous five years with the legacy fleet of motors. It also conducted operator interviews, which concluded that the drive for faster drilling would continue and that rig contractors were continuing to upgrade top drives and mud pumps to generate more hydraulic horsepower.

Based on these data, Baker Hughes constructed the operational envelope, motor configurations and technical capabilities required for the next generation of motors. The resulting Navi-Drill DuraMax high-performance downhole motor is specifically designed for unconventional applications by providing increased horsepower, torque and durability.

Baker Hughes tested the Navi-Drill DuraMax motor at its Baker Hughes Experimental Test Area (BETA) near Tulsa, Okla., prior to going into the field test stage. Key learnings from the BETA test proved that the design was able to withstand the desired operational envelope and the conceptual design performed as expected. After the BETA test, Baker Hughes ran almost 40 field tests to confirm that the motor would provide not only the performance but also the durability that was expected. The team made a few enhancements to bolster the ability to drill ahead “straight” in rotary mode for longer intervals without the need to slide for corrections as frequently. It also made minor adjustments to assembly procedures and minor design improvements to increase life expectancy of components.

Baker Hughes commercialized the Navi-Drill DuraMax motor in early 2019, consistently outperforming drilling rates in offset wells with major penetration rate improvements of 30% or more.

A key factor in the performance gains has been the directional response. The short bit-to-bend distance for the adjustable kickoff of the motor delivers a more consistent buildup rate. The directional response in the lateral is immediate and less footage is required to slide to get back to the target line. The immediate and precise directional response means the motor can achieve the dogleg severity required and still deliver good penetration rates, often a trade-off with other motors.

Case studies

An operator in North Dakota’s Williston Basin was looking for ways to improve drilling efficiency. This operator had been using motors from a competitor along with a few runs using motors from Baker Hughes. Baker Hughes proposed to the operator a trial of its new Navi-Drill DuraMax high-performance motor.

The 5⅛-in. Navi-Drill DuraMax motor delivered a record-breaking performance on the first run. The lateral was drilled in 1.94 days (from drillout to total depth), which was the fastest lateral drilling time on this rig. This equated to a 40% time savings and an increase of 35% in ROP, compared to the average well drilled on this rig.

In all, Baker Hughes completed three runs with an average run time of just over two days each, delivering “mile-a-day” drilling performance and saving more than five drilling days total for this operator. Impressed with the performance of the Navi-Drill DuraMax motor, the operator requested that Baker Hughes use it 100% of the time on three of its rigs.

In another instance, an operator in the Permian Basin contacted Baker Hughes to provide a solution that would reduce the amount of time spent in drilling curve and lateral hole sections. The wells in this area of West Texas typically require a steerable motor with a high adjustable kickoff setting to achieve the buildup rate necessary to drill the curve section. However, a high adjustable kickoff setting can compromise the ROP in the lateral section.

The Baker Hughes team recommended the Navi-Drill DuraMax high-performance drilling motor to improve performance and reduce the number of trips made for new motors and bits through the curve and lateral sections. The shorter bit-to-bend distance for adjustable kickoff of the motor successfully drilled the high buildup rate curve section. The rugged motor design also enabled the operator to rotate the drillstring at a higher rpm and a high weight-on-bit, compared to offset runs, and delivered optimized performance in the lateral section.

The 5⅛-in. Navi-Drill DuraMax motor drilled the 6¾-in. curve and lateral section in the Wolfcamp A Formation. The motor drilled 7,652 ft in 80 drilling hours and maintained an average ROP of 114 ft/hr. The motor delivered a consistent buildup rate in the curve, exceeding expectations.

By drilling 3,127 ft laterally in one day, Baker Hughes provided a 30% improvement in overall ROP, which saved the customer three days in rig time.