Oil Rig Ballast Control System Accidents

P-36

Ballast control systems are a vital part of semi-submersible oil platforms. The ballast control system is made up of a network of pipes, valves, pumps, and tanks, which work as a liquid control system to keep the vessel at an even keel. Offshore drilling is an extremely risky undertaking, which is susceptible to accidents, which may cause human casualties and environmental disasters.

One of the key systems necessary to keep oil rigs afloat, is the effective design of the user interface for the ballast control system, which significantly contributes to overall safety of a rig’s crew and the environment. The threat of disaster is the main reason to provide the operators with the most effective ballast control system possible. One such disaster occurred in 2001 aboard Petrobras’ P36 oil rig. At the time, this was the largest offshore oil rig in the world. The rig was located in the Roncador field in the Campos Basin the offshore Rio de Janeiro. Unfortunately, on March 15, 2001, the rig began to sink after a series of explosions.

A range of small, improbable events came together to cause this disaster. Shortly after midnight on March 15, the starboard drain storage tank ruptured, which released gas, oil, and water into the fourth level of the starboard aft column, the column in the right, rear quadrant of the vessel. These materials were able to flood the column because of a series of faulty pumps and valves that were part of the ballast control system. The gas and oil found an ignition source at the top of the column and caused an even larger chemical explosion. This explosion killed the 11 emergency firefighters that had responded to the first explosion.

The ballast control operators tried to stabilize the vessel by moving water into the portside forward column to counter-balance the flooding on the opposite side. Their efforts failed and they were unable to regain balance, forcing the evacuation of nonessential personnel at 1:44 am. Helicopters rescued the final crew members at 6 am and 164 of the 175 crew members survived this disaster. Crews attempted to flood the ballast tanks and columns with nitrogen to salvage the rig, but these attempts proved futile as the platform sank into the Atlantic Ocean five days after the explosions. Cleanup crews treated approximately 350 cubic meters of oil that had spilled into the ocean. Petrobras estimated losses of US$100 million per month following the disaster.

Just four days ago, on March 2nd another ballast control problem occurred at the SS-53 'Paul Wolff"rig, belonging to Noble do Brasil, which is on lease to Petrobras and was undertaking well re-entry and completion procedures on well 7-MRL-222HPA-RJS at the Marlin Field in the same Campos Basin 126 km from the coast of Rio de Janeiro. At around 1 am, one of the ballast tanks flooded due to a defect in a key ballast control valve. With the flooding the rig took on a 3,5 degree list, forcing 77 workers to be evacuated, while another 36 workers remained aboard to pump out the water, which also flooded one of the ballast control rooms.

As there was no rupture in oil or gas tanks or pipes, there was no risk of an explosion and as the wellhead was still capped at the time, there was no risk of oil spilling from the well. Obviously, this was a minor accident if compared to the P-36 disaster, yet it is a good example of the thin red line that exists between safe operations and accidents on offshore rigs due to problems emanating from ballast control systems. In future posts we will take a closer look at the mechanisms involved in Ballast Control Systems on offshore drilling rigs.

P-36

P-36

P-36

Noble SS-53 'Paul Wolff'

SS-53

P-36

P-36