Negative Operational LL with Wellesley

Songesand (35/4-2) – P&A

What happened:

As on all previous wells, with the well displaced to seawater and wellhead cutting operations started, 200 m3 1.50 sg kill mud were mixed in the surface pits and sent to the column tanks for the rig move. Weather delays meant it stayed in the column tanks for over a week. The mud was circulated 4-5 hours each shift. Unbeknown to everyone, the barite settled out and the rheology deteriorated which resulted in barite dropping out and eventually plugging the suction line. This manifested itself when a transfer pump ran dry, overheated and caused a smoke alarm on the bridge, resulting in a muster to emergency stations. After the muster and recovery operation, suction was eventually regained by priming the back-up transfer pump with drill water in the pump room of the column tank.

What was planned:

Mix kill mud prior to rig move.

What was learned:

The difference on this well was the time spent WOW after the mud was mixed ( > one week). In the future it is recommended to not only circulate the tank, but to transfer a sample back up to the surface pits so that the weight and rheology of the column tank contents can be checked.