Near Miss - Wireline unit failed to stop

Wireline crew had just made up toolstring, stabbed on lubricator and pressure tested the stack. They then equalised and opened the well to run in hole, they released the tools from the tool catcher and confirmed it had released by applying 2 x hand jars.

On confirming that the tools had released, the Wireline unit began picking up on the tool string on its own accord. The tension alarms sounded, however the winch did not cut out. The cable pulled out of the cable head and landed on the deck with the tools falling down hole.

The check valve in the grease head functioned and no hydrocarbons were released, the well was made safe and the lubricator was bled down. Offshore crew then called onshore support to report and discuss events.

As part of the investigation into the incident it was identified that when changing out the high tension shut down valve, the hoses had been installed incorrectly meaning that when the unit was sitting idle, the hydraulic fluid which would normally circulate back to the tank was allowed to bypass and build up pressure allowing the unit to function. This also meant that the emergency tension shut down was unable to function and explained why the unit continued to operate when the alarms sounded.

When the unit is functioned and operated there is no visual or tell tale that the hoses are installed incorrectly but only when the unit is left running in neutral for an extended period of time.

The hoses were changed and the valve and hoses were marked to show correct alignment. Other units were checked both offshore and in base to ensure that no other units were similar.

Additional actions were also implemented to ensure similar events would not take place.