Two new rotary steerable systems tackle tough directional drilling challenges.

Schlumberger has added two new rotary steerable systems (RSS) to its PowerDrive RSS family of services: a powered RSS for fast directional drilling in tough, hard-rock formations and a rugged RSS for precise directional control in harsh, high-temperature environments. When providing directional drilling services, the company's objective is to drill from shoe to total depth in one run at maximum rate of penetration (ROP). According to the company, both of these high-performance drilling systems were developed with that objective in mind. All PowerDrive RSS external parts rotate, a feature that has proven to generate dramatically increased ROP. Full rotation also helps clean and condition the hole which, in turn, reduces drilling torque and the risk of differential or mechanical sticking. According to Schlumberger, the use of both systems, with their increased functionality, reliability and attributes tailored for specific directional drilling scenarios, can directly and substantially reduce costs while maximizing production rates and ultimate recovery in wells drilled worldwide.

Precise directional drilling

The new generation PowerDrive X5 system from Schlumberger is its first RSS with integrated measurements to optimize drilling performance and wellbore placement in challenging applications such as hot holes and offshore wells. The system's reliability and efficiency exhibits up to 15% step-change in improvement compared to previous systems, enabling reduced drilling times, extended runs and optimized wellbore placement for significant, direct cost savings. Substantially improved reliability has been achieved through the new RSS design that includes a simple but rugged high-performance steering section. Reliability and durability also have been improved through chassis-mounted electronics, that can withstand downhole temperatures as high as 302°F (150°C), allowing the system to operate reliably in harsh, hot environments. RSS electronics are based on the company's PowerPulse measurement-while-drilling (MWD) telemetry technology.

The X5 system incorporates a real-time, near-bit azimuthal gamma ray sensor with 360° borehole imaging for geosteering applications, providing formation and structural information close to the bit for timely decision making. An MWD-type, near-bit triaxial sensor package provides accurate azimuth and inclination information that enables control of both directional response and true vertical depth (TVD) in either automatic or manual operation mode. Having available real-time, near-bit gamma ray and directional measurements, including azimuth, ensures efficient drilling in reservoirs that require geosteering precision and TVD accuracy. The azimuthal gamma ray sensor situated just over 6 ft (2 m) from the bit empowers drillers and geologists with real-time information to identify formation dips and/or fault boundaries and take timely action to optimally place the well bore. Aiding steering decisions, these formation and structural changes are revealed by a real-time 360° gamma ray image of the well bore. Near-bit formation evaluation, precise directional steering and tight true vertical control work together to maximize the length of drainhole in the target pay. The combination also improves casing and coring point detection, minimizes penetration of core-targeted formations and significantly reduces chances of drilling through a potentially valuable core section or spending time and money coring a nonproductive formation.

An automatic inclination hold function and efficient downlink system minimize the needed interaction with the directional driller to maintain directional control while drilling ahead in tangent and horizontal sections. Improved downlinking permits commands to be made while drilling, reducing the time once needed to downlink. This, and trajectory lock-in via inclination hold enables the system to steer automatically upon penetrating the target formation, decreasing the time required for surface directional input and therefore increasing productive time on bottom. A smooth tangent section and TVD in the horizontal section are ensured, critical for maximizing ultimate recovery and the well's producing rate potential.

Like every PowerDrive RSS, the X5 system is fully rotating, which increases ROP and improves hole cleaning to reduce drilling torque and the chance of differential or mechanical sticking. The X5 system's automatic trajectory functionality coupled with the full rotation increases wellbore smoothness and decreases tortuosity, which improves drilling efficiency and eliminates the need for unplanned wiper trips. A better quality well bore facilitates running casing and performing well work down the road, such as coiled tubing intervention and electrical submersible pump installation. Advanced coating materials that mitigate wear ensure reliable, consistent performance in a wide range of drilling environments. Optimized flow profiles also reduce the risk of sticking, in addition to limiting the effects of mud solids and erosion of internal and external downhole components.

Faster, powered directional drilling

The PowerDrive Vortex RSS has a fully integrated, high-torque power section that converts mud hydraulic power to mechanical energy which, when combined with surface torque generated by the rig's top-drive, significantly increases torque capacity and rotation speed at the bit for faster drilling in hard formations. According to Schlumberger, the additional torque results in increased ROP and more cost-effective drilling. The system's bearing package and transmission section are designed specifically for high-operating loads, ensuring reliable, efficient drilling performance during extended runs.

The powered RSS also operates at higher revolutions per minute (RPM), optimizing polycrystalline diamond compact bit performance for greater ROP and drilling efficiency. The increased torque and RPM combination of the high-performance system translates to faster ROP, greater drilling efficiency and longer runs. This, in turn, generates rig-time and drilling cost savings. Also, powered RSS technology can be used to expand the operating envelope of a rig with low torque capacity and insufficient power to rotate the drill string itself, thereby improving directional performance and drilling efficiency during conventional directional drilling operations.

Compatible with a wide range of drill string rotation speeds, the Vortex system's integrated power section optionally slows drill string rotation while it rapidly rotates the bit. This reduces stick-slip phenomenon and other damaging vibration modes associated with conventional RSS drilling. As a result, all available energy is used to maximize ROP and drilling efficiency. Minimizing vibration modes reduces the risk of damaging the bottomhole assembly. Slower drill string rotation also lessens the risk of casing wear and drill string fatigue in sections with high dogleg severity, reducing the chances of drill string or casing failure.

The system has multiple stabilization options. The RSS can be stabilized at any of four locations along its length, which permits it to be tailored to a specific directional drilling situation for optimum performance. Additionally, the powered system has an optional inclination hold function that allows a tangent or horizontal section to be drilled automatically, without intervention from the directional driller. This automatic downhole control makes it possible to drill a hold section more accurately and quickly than a conventional surface-operated control setup.

As in every PowerDrive RSS, all external parts of the Vortex system rotate, which further improves ROP and hole cleaning as well as reduces drag problems and sticking risks. According to the company, the new Vortex RSS is taking on many tough challenges, for high ROP drilling in hard-rock and other harsh environments, both on- and offshore alike.

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