Equipment Collapse During Workover Operation Results in a Serious Near Miss

United States Department of the Interior

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Kumkum Ray
703-787-1604

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OMM Web Team

National Safety Alert No. 7
July 28, 2003

Equipment Collapse During Workover Operation Results in a Serious Near Miss

During a recent workover operation using a jack-up lift boat positioned next to a satellite well, a snubbing unit mast and gin pole assembly fell from the wellhead after one of the assembly’s anchor points failed. The mast and gin pole assembly was about 98 feet in length and weighed 36,000 pounds. The incident caused relatively minor damage to equipment on an attending marine vessel and the vessel’s bulkhead. Although no injuries, pollution, or significant property damage resulted from the incident, the consequences could have been much worse.

The snubbing unit was located on the lift boat, and the unit’s mast assembly was secured by guy wires extending to three fixed and one temporary anchor points. The temporary anchor point was a set of two 4,000-pound cement marine blocks placed in 8-9 feet of water on the sea floor. At some time during the workover operation, the marine vessel, with a draft of 8 feet, was positioned alongside the lift boat within 10 feet of the cement blocks so that equipment on the vessel could be rearranged and offloaded. The vessel worked in this location for approximately 1-1/2 hours and, because of strong currents, used its reverse prop thrusters for stabilization. Within a half hour of the vessel moving from that location, the snubbing unit mast assembly fell.

The MMS investigation concluded that the immediate cause of the snubbing unit’s collapse was the prop thrusters’ wash disturbance of the unconsolidated seafloor under the cement blocks, resulting in the movement of the blocks and a subsequent slackening of the attached cables. The failure of the operator and contractor to adequately plan the snubbing operation and address the potential hazards was evidenced by: 1) the use of an 8- foot draft marine vessel in 8-9 feet of water, 2) operating the marine vessel in close proximity to the temporary anchor for an extended period of time while currents were running strong, and 3) the placement of the temporary anchor on the seafloor where unstable conditions existed.

MMS recommends that all operators and contractors thoroughly review their procedures for workover operations. Operators and contractors should ensure that they have evaluated all hazards associated with the planned activities and have effectively implemented safe work practices to address these hazards. For workovers in shallow water that will not be conducted from a fixed platform, close attention should be paid to the hazards and safe practices associated with anchor location and the operation of marine vessels in the vicinity of snubbing units and other workover equipment.

For further information, please contact Melinda Mayes, (703) 787-1064.

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Last Updated: 02/01/2006, 12:48 PM