Schlumberger

Performance Report: KLA-SHIELD System Exhibits Excellent Performance in Alaskan Shale and Clay Formations

Challenge:

  • The operator wanted to drill the wells and run 7-in. long string casing to minimize time and cost by eliminating an intermediate interval.
  • Successfully drilling and running a long string required drilling through depleted production sands to the normally pressured target zone with the inherent risks of stuck pipe, losses, wellbore stability problems and well control.
  • Adding to the challenge were highly reactive clay/shale, coal beds and sands in the producing zones with high concentrations of interstitial shale.
  • Due to environmental concerns and logistical challenges, oil-based or synthetic-based fluids were not an option.

Solution:

  • A KLA-SHIELD system was proposed for this “S”-shaped well.
  • This water-based mud system is designed to provide shale stabilization and reduce the swelling of sensitive shales and drill cuttings exposed to water-based drilling fluids.
  • Formation samples were evaluated using mineralogy, cation exchange capacity, thin-section analysis and fracture development tests performed in the M-I SWACO Houston laboratory. These tests identified the best inhibitor/stabilization package and the concentrations required to deliver optimum performance while drilling the production interval.
  • Key products used in the KCl-based KLA-SHIELD system in this Alaska field were KLA-STOP shale inhibitor, SACK BLACK shale inhibitor, SAFE-CARB bridging agent (using OPTIBRIDGE for particle size distribution, PAC SL polymer, and sulfonated asphalt. LO-TORQ, and LUBE-776 lubricant were used to decrease torque in the wellbore.

Result:

  • The well was drilled with no losses, stuck pipe or wellbore stability problems. Total time from spud to landing a 7-in. long string casing, including four days of openhole logging, was 18 days with no lost time due to mud problems.
  • The KLA-SHIELD system provided excellent inhibition of reactive shale and clay, producing crisp annular cuttings.
  • The mechanically sensitive shale remained stable.
  • Drilled through depleted zones with formation pressures of 3.5 lb/gal estimated mud weight (EMW) and equivalent circulating densities of ~10 lb/gal EMW with no losses.
  • The well was drilled in five days, 6.5% shorter than the time planned and at 23% lower than planned costs.

Well Information
Location Alaska
Interval drilled 12¼ in. 70 to 3,041 ft (21 to 927 m)
Interval drilled 8¾ in. 3,041 to 7,005 ft (927 to 2135 m) (“S”-shaped well)
Disposal method Injection
Bottomhole temperature 110°F (43°C)
Density required 9.8 lb/gal (1,174 kg/m3)
Completion type Conventional gravel pack and 3-zone multi-gravel pack
Mud weight 9.8 lb/gal
Casing size 12¼-in. (casing: 9⅝ in.) and 8¾ in. (liner: 7 in.)
Total well depth 7,005 ft (2,135 m) [6,780 ft (172 m) total vertical depth]

Two wells were planned for the 2008 drilling program. This “S”-shaped well was drilled in two intervals, 12¼-in. surface and 8¾-in. production. The production interval was to be drilled and a 7-in. long string casing placed through an unconsolidated, underpressured formation to the normally pressured target.

A three-day openhole logging run only magnified the concern of maintaining adequate wellbore integrity to allow the 7-in. long string to be landed. Other concerns that were successfully avoided includes lost circulation, stuck pipe and well control problems.


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“Because of wellbore integrity afforded by the KLA-SHIELD system drillers were able to land a 7-in. openhole logging string through an unconsolidated and underpressured formation without difficulty.”
Jim Cucullu
Project Engineer
M-I SWACO