Two sets of seven unconventional wells in the Permian Basin were planned with aggressive curves. The dogleg severity (DLS) demanded for these curves was a sharp 8° to 11°. Compounding the challenge was that these wells fall within the zone of exclusion—a narrow north–south window with azimuths between 160° to 200° (southerly) and 340° to 20° (northerly)—which can further destabilize azimuthal headings already stressed by the formation’s inherent shock and vibration characteristics.
Drilling curves using rotary steerable systems previously required what is referred to as “manual mode,” which involves a sequence applied repeatedly to control the curve trajectory. This sequence comprises multiple interventions and downlinks from the directional driller at the surface for steering force, toolface (TF) orientation, and measurements. Consequently, cycle times can be as long as 20 minutes and lead to additional time, tortuous curves, and reduced ROP.
SLB recommended deploying the PowerDrive Orbit G2™ RSS and xBolt G2™ accelerated drilling service with the autonomous downhole control system—in this instance, the auto-curve and auto-lateral components. These capabilities bundle all the steps of manual mode into a single downhole autonomous control process that begins with the directional driller downlinking the required DLS and TF orientation on the well plan. The RSS receives the command downhole and automatically adjusts its steering force and TF to match the DLS and TF orientation.
Additionally, the BHA tracks its continuous inclination and azimuthal using sensors close to the bit (3-axis inclinometers and triple 3-axis magnetometers). ROP data enables the RSS to compute its resulting DLS and TF. Each second, the tool adjusts its steering parameters to meet the designated trajectory, functioning without the need for surface control, which means fewer downlinks and less time lost to the cycle. The technology makes frequent and small adjustments, resulting in less tortuosity compared with the infrequent and violent surface control. Freed from trajectory concerns, this enables the directional driller to focus on drilling efficiency.
The autonomous downhole control system drilled curves and laterals in 14 wells in their 6¾-in sections. Results observed across each well were compared with nearby offsets for curves drilled in manual mode. Downlinks to the PowerDrive Orbit G2 RSS were reduced as much as 55% in seven curves and 42% in the remaining seven curves.
ROP also increased in all the curves using the auto-curve component. Ten of the 14 wells were drilled in a "pure” north—south azimuthal window and despite severe shock and vibrations at very high rpm.
