Well Control – Loss of Primary Control

Well Control - Loss of Primary Control

There are four principal causes of loss of primary control: swabbing, insuficient fluid density, losses, failure to fill the hole correctly.

1 Swabbing

Swabbing can also be caused by pulling full gauge tools which restrict the passage of fluid in the annulus. This creates a piston effect and the volume below the tool would be filled by the fluid inside the drillstring, causing a large drop of the fluid level in the drillstring and consequent dangerous reduction in hydrostatic head. "High Volume" swabbing is especially dangerous in large diameter holes.

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