DAILY NEWS May 10, 2010 9:45 AM - 1 comment

Understanding the initial Deepwater Horizon fire

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By: Guy Crittenden

As people read about the growing environmental disaster of a spreading oil slick from below the now-destroyed Deepwater Horizon drilling rig in the Gulf of Mexico, they may have lost track of the original story of the rig fire three weeks ago that burned for two days, causing the rig to sink in 5,000 feet of water and killing 11 men while injuring others.

Details about the fire and how drilling rigs like the Deepwater Horizon function and malfunction are important to understand and remember, apart from the unfolding story of the environmental impact.

Although this has become a "BP (British Petroleum) story," the rig itself belonged to Transocean, the world's largest offshore drilling contractor. The rig was contracted through the year 2013 to BP, which put it into service working on BP's Macondo exploration well (where it was located when the fire broke out).

Such rigs cost about $500,000 per day to contract; a full drilling spread with helicopters and support vessels and other services cost closer to $1 million per day to operate while actively drilling for oil and gas. (The rig cost about $350 million to build in 2001 and would cost at least double that to replace nowadays.)

Despite it being destroyed, the Deepwater Horizon rig represents the cutting edge of drilling technology. It's a floating rig, capable of working in up to 10,000 feet of water. Such rigs aren't moored; anchors would be too costly and too heavy to suspend from the floating structure. Instead, a triple-redundant computer system uses GPS satellite positioning to control powerful thrusters that keep the rig positioned within a few feet of its intended location, at all times. This is called Dynamic Positioning.

The Deepwater Horizon had apparently just finished cementing steel casing at depths exceeding 18,000 ft. The next operation was to suspend the well so the rig could move on to its next drilling location. (The rig would return to this well later in order to complete certain task to bring the well into production.)

Experts speculate that the fire was caused by formation fluids - oil /gas - that got into the wellbore and were undetected until it was too late. In floating drill rig setups, all the main pressure control equipment sits on the seabed because they move with the waves, currents, and winds. This constitutes the uppermost unmoving point in the well.

This pressure control equipment - called Blowout Preventers or "BOPs" - are controlled with redundant systems from the rig. In the event of a serious emergency, multiple panic buttons are available to hit, and even fail-safe Deadman systems that are automatically engaged. The fact that none of these were activated (at least, not successfully), suggests that the blowout was especially swift and came to the surface rapidly.

The flames were visible up to about 35 miles away. Not the glow, the flames! These were 200 to 300 feet high.

The well is still spewing oil at a rate of about 5,000 gallons per day, and wind and weather has defeated efforts to cap the well and contain the slick at the surface. The slick is now moving toward Texas and Louisiana, threatening sensitive environments and important fisheries.

Attempts to cap the well have utilized the same remotely operated vehicles (ROVs) used in regular underwater oil and gas production. ROVs are tethered miniature submarines with manipulator arms and other equipment that perform work directed by operators aboard floating vessels. (Such craft were used to explore the Titanic.) Every floating rig has at least one on board, in almost constant use. In this case, ROVs are from dedicated service vessels.

In addition to attempting to lower a massive concrete dome over the well on the seabed, another dimension of the response will be to move at least one other rig to drill a fresh well that will intersect the blowing one at its pay zone.

The technology will again be attached to a floating rig, capable of drilling over three miles deep to a specific point in the earth with a target radius of just a few feet plus or minus. Once the operators intersect their target, a heavy fluid will be pumped that exceeds the formation's pressure, causing the flow to cease and rendering the well safe at last.

It will take at least a couple of months to get this done, bringing all available technology to bear. The ecological disaster will be enormous if the well flows all this while.

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Reader Comments

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Ozark Jim

Its amazing that BP had not test disaster recover processes and tools before starting production pumping. The top hat should have been tested day one. Also a relief well needs to be drilled day one that intersects the main shaft so that the main shaft can be plugged very quickly. A heavy duty metal cage needs to be place over the well head area on the ocean floor to protect it from a sinking platform. It's just amazing this type of disaster could occur in this day and time based on what we have learned from the past. Business process have not changed regarding insuring that all operations are extremely safe for both operations personal and the environment. Someone was a sleep at the wheal on this one.$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

Posted May 12, 2010 04:34 PM

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