Schlumberger

Case Study: Ultradeep, Ultrahigh-Pressure Sidetrack Drilled for USD 21 Million Below AFE

Each section of reentry well drilled to TD in a single run with no NPT in Gulf of Mexico

Challenge: Drill reentry sidetrack in harsh environment with low fracture gradient and tight mud-weight window to evaluate ultradeep, ultrahigh-pressure reservoir in Gulf of Mexico.

Solution: Use operator’s stress cage lost circulation material mix to strengthen wellbore and Schlumberger rotary steerable directional drilling, drilling optimization, MWD, and LWD services, including PowerDrive X5 RSS, sonicVISION sonic-while-drilling tool, arcVISION array resistivity compensated tool, and PERFORM Toolkit data optimization and analysis software.

Result:

  • Well cost was approximately USD 21 million under AFE and USD 4.3 million less than target cost.
  • Each well section was drilled to TD in a single run with no NPT.
  • Ultradeep, ultrahigh-pressure reservoir was successfully evaluated.

Overcome challenges

An operator was drilling a deepwater reentry sidetrack well to evaluate a reservoir in the Gulf of Mexico. Because well control and pore pressure issues had made evaluation impossible in the discovery well and the initial appraisal well, the operator considered successful evaluation a financial imperative. Achieving that success would require overcoming many challenges, including a low fracture gradient, a tight mud weight window, the ultradeep planned TD of more than 32,000 ft MD, and an ultrahigh bottomhole pressure expected to exceed 25,000 psi.

Optimize drilling

Working with the customer, Schlumberger overcame those challenges. The operator’s stress cage lost circulation material mix was used to strengthen the wellbore while drilling, and Schlumberger provided rotary steerable directional drilling, MWD, LWD, and drilling optimization services. LWD technology included the sonicVISION sonic-while-drilling tool for real-time pore pressure prediction to optimize mud weight and the arcVISION array resistivity compensated tool. PERFORM Toolkit data optimization and analysis software aided drilling optimization.

The drilling team milled a window and set a 13 5/8-in whipstock at the deepest a whipstock that size had ever been set, then kicked off the 12 1/4-in × 14-in hole section to drill it in a single run, despite the harsh drilling environment in the Eocene interval. Close monitoring of BHA drilling dynamics enabled the team to keep shocks and vibration as low as reasonably practicable and to maximize ROP by optimizing the mechanical specific energy transferred to the bit and reamer.

After setting an 11 7/8-in liner, the team drilled the 10 5/8-in × 12-in hole section, where high-to-severe stick/slip was encountered and the string often stalled out in the interbedded ratty formations. Using PERFORM Toolkit software, the drilling optimization engineers concluded that both the bit and the reamer were stalling out at the same depth, indicating that the reamer was still opening while drilling and that steady torque rather than steady weight on bit should be used while drilling the rest of the section. The team considered tripping the BHA to inspect the bit and reamer but decided to continue drilling—a decision that proved correct when the bit and reamer were found to be in much better condition than expected at the end of the run.

Drilling of the 10 5/8-in × 12-in hole section took approximately 14 days, with 335.5 h spent below the rotary table. Pumping accounted for 264.8 h of that time, and 172.0 h were spent drilling on bottom. The annular pressure at well TD was 26,419 psi and the formation pressure was calculated to be approximately 25,990 psi—higher than in any previous Gulf of Mexico well. Maximum bottomhole temperature while circulating was 228.2 degF.

Evaluate discovery

Schlumberger drilled each hole section to its TD in a single run, with no NPT. The operator’s cost for the ultradeep, ultrahigh-pressure well was approximately USD 21 million less than the AFE cost and USD 4.3 million less than the target cost.


Download: Ultradeep, Ultrahigh-Pressure Sidetrack Drilled for USD 21 Million Below AFE (0.68 MB PDF)

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