Purpose
The Underbalancing Pressure Sub - Ported version, is used in a perforating system to provide an economical method of achieving an underbalanced condition between the tubing and the wellbore formation. The tool incorporates a high strength ceramic dome which prevents communication between the tubing and annulus until a detonating bar is dropped from surface. The ported sub is normally run below a packer system, the ports are located below the ceramic dome to allow flow into the tubing.

Operation
The ported underbalancing pressure sub is installed in the tubing string normally below a packer system to create the desired underbalanced condition as well as replaces a fill-flow sub assembly. The ported section is located below the ceramic dome, this ported section area is always equal to or greater then the tubing i.d. cross sectional area which does not restrict or choke the wellbore flow into the tubing once the dome has been shattered from the drop bar passing through the tool.

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