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Case Study: Shell Brazil Achieves High Inclination in Soft Formation

BHA with rotary steerable system and tricone bit drills 17 1/2-in tophole section of deepwater well from vertical to 49.7° inclination at 45 m/h average ROP

Challenge: Drill 17 1/2-in tophole section of deepwater well from vertical to inclination of 50° in soft formation while maximizing ROP and ensuring high borehole quality.

Solution: Build angle with BHA incorporating

  • PowerDrive Xceed rotary steerable system for harsh, rugged environments
  • Smith Bits tricone bit
  • arcVISION825 8 1/4-in drill collar resistivity tool
  • TeleScope high-speed telemetry-while-drilling service.

Result:

  • Achieved inclination of 49.7° at section TD with average dogleg severity (DLS) of 2.4°/30 m and average ROP of 45 m/h.
  • Ran 13 3/8-in casing string to bottom.

Build angle in tophole sections

Shell Brazil had been drilling deepwater wells targeting reservoirs located 1,000 m or less below the mudline. To drill the wells’ reservoir sections horizontally, it was necessary to build angle in their tophole sections, which was difficult because the formations were soft and unconsolidated. Tophole sections of the initial wells were drilled with motors and 16-in tricone bits. These BHAs were sliding two-thirds of the time—limiting average ROP to about 10 m/h— and could only achieve inclinations between 21° and 36° by section TD.

In later wells, the tophole sections were drilled with BHAs incorporating a 9-in PowerDrive Xceed rotary steerable system (RSS) for harsh, rugged environments, a 12 1/4-in polycrystalline diamond compact (PDC) bit, and a 17 1/2-in under-reamer. These BHAs eliminated the need for sliding, increasing average ROP to about 35 m/h, and delivered inclinations of 25° to 40° at section TD. Shell Brazil wanted to further improve drilling performance to achieve an inclination of 50° at section TD while maximizing ROP and ensuring high borehole quality.

Use an integrated solution

Schlumberger met Shell Brazil’s objectives by incorporating best practices and lessons learned from 9-in PowerDrive Xceed operations worldwide and taking full advantage of the RSS’s large-hole DLS capabilities. Extensive modeling and simulations of BHA tendency, hydraulics, and torque and drag, together with the lithology directional tendency in the area, were used to select the most efficient set of drilling parameters, the proper type of bit, and the hydraulic horsepower per square inch (HSI) required. As part of the integrated solution, Smith Bits and M-I SWACO conducted risk analysis and modeling to help determine the best borehole stabilization profile, BHA design, bit HSI, and hole cleaning strategies.

In addition to the PowerDrive Xceed RSS, the BHA included a 17 1/2-in XR+VE3JPS tricone bit, which improved hole cleaning by eliminating the need for an under-reamer. The BHA also included an arcVISION825 8 1/4-in drill collar resistivity tool, and the TeleScope high-speed telemetry-while-drilling service. The arcVISION825 tool provided array compensated resistivity and APWD annular pressure-while-drilling measurements that were sent to the surface in real time by the TeleScope service, along with vibration and IWOB integrated weight-on-bit measurements.

Achieve planned inclination at high ROP

Despite the soft, unconsolidated formation, the point-the-bit PowerDrive Xceed RSS achieved an inclination of 49.7° at section TD, with an average DLS of 2.4°/30 m. ROP averaged 45 m/h and at times reached 80 m/h. The high-quality borehole enabled the drillstring and BHA to be tripped out of the hole with minimum drag and the 13 3/8-in casing string to be run to bottom. This performance made this PowerDrive Xceed BHA the front runner for upcoming campaigns involving eleven 17 1/2-in tophole sections and for development of a potential field to produce a relatively shallow reservoir roughly 700 m below the mudline.


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