Performance Report: SACK BLACK Enhances High Performance WBM, Eliminates Casing


Challenge: The operator wanted to drill the wells and run 7 in. long string casing, which would eliminate an intermediate interval and, thus significantly reduce time and cost. The objective was to drill and run the long string through depleted production sands to the normally pressured target zone.

Solution: The M-I SWACO Houston lab performed characterization and analysis of formation samples with Mineralogy, CEC, Thin Section Analysis and Fracture Development tests. The test results lead M-I SWACO to recommend the operator use the Kla-Shield water base mud designed to provide wellbore stabilization by sealing microfractures in shale/coal formations and inhibiting the swelling and dispersion of sensitive shale and drill cutting exposed to water-based drilling fluids.


  • The well was drilled with no losses, stuck pipe or wellbore stability problems. Total time from spud to landing the 7 in. long string casing, including four days of open hole 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 angular cuttings
  • The mechanically sensitive shale remained stable
  • Drilled thru depleted zones with formation pressures of 3.5 ppg EMW to TD with pressures of ~9.8 ppg EMW and ECD’s of ~10 ppg EMW with no losses.

The Details

This S shaped well was drilled in two intervals, 12 ¼ in. surface and 8 ¾ in. production. Of particular concern was drilling the production interval and running 7 in. long string casing through the unconsolidated, depleted formation just below the casing shoe, to the normally pressured target formation. A three-to-four day open hole 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 included lost circulation, stuck pipe and well control problems.

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