OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 37 Oil and Gas Wells

Section 780 Well swabbing

Swabbing involves pulling a rubber-faced cylinder i.e. a swab, up the well tubing which lifts the column of fluid above it to the surface. This reduces the pressure beneath the swab and sucks fluids out.

This swab is typically run through a pressurized lubricator connected to the top of the well Christmas tree. The process is called “snubbing”. This must be securely anchored to ensure that there is no break at the connection point.

As long as there is adequate lighting, swabbing, as part of well testing, may be conducted during darkness until hydrocarbons appear at the surface. At this point the recovery must be reverse-circulated. Reverse circulation is the intentional pumping of fluids down the annulus i.e. area of the well bore that is outside the drill pipe, and back up through the drill pipe. This is the opposite of the normal direction of fluid circulation in a well bore. A pump-out sub is typically in the test string in order to reverse.

Reverse circulation requires proper disposal of the contents of the drill string by pumping to a tank or a vacuum truck. The receiving vessel must be properly grounded and vented with any engines turned off. Extra care must be taken once the pump-out sub has reached the rig floor since hydrocarbons may be present below the pump-out sub.