The Situation

• 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

The 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.

The Results

• 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

The Details

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.

Questions? We’ll be glad to answer them.

If you’d like to know more about the KLA-SHIELD product and how it’s performing for our other customers, please call the M-I SWACO office nearest you.