A well kick, during a wiper trip, recently occurred on a floating drilling vessel due
to loss of mud column pressure by swabbing. When the expanding gas forced mud out of the
riser onto the rig floor, an employee broke his leg by accidentally stepping out of the
"V" door while attempting to leave the rig floor. The volume of mud that was
being swabbed from the hole was apparently lost out of a leak in the riser rather than
flowing out the flowline. Initial detection of such a surface flow would have served as an
early warning of the influx of gas, into the well bore, by swabbing.
A riser leak can prevent early detection of swabbing. To avoid this in the future, the
operator plans to scan the riser by TV prior to trips. Observing the riser-fluid level
under static conditions is also an effective means of detecting fluid loss. If the fluid
level is dropping, the rams should be closed, the riser refilled, and the fluid level
again observed, to determine if the mud is being lost through a riser leak or into the
formation.
