The first attempt to contain leaking crude oil from the Macondo well and funnel it to a drillship 5,000 feet above failed after gas hydrates accumulated inside the cofferdam and plugged up the top of the dome, BP reported Saturday.
"I wouldn't say it's failed yet," BP Chief Operating Officer Doug Suttles said Saturday afternoon of the subsea containment strategy. The BP executive said that his company is now looking for a way to overcome this latest challenge, tapping expertise from throughout the oil and gas industry for possible solutions.
Slushy hydrates, ice-like crystals produced by the combination of natural gas and water at certain temperatures and pressures, had been expected to form inside the riser system proposed to link the cofferdam to the drillship. Pumping warm seawater from the surface into the annular space between the inner and outer risers has been advanced as a potential remedy for this scenario. Hydrate formation inside the containment dome and resulting blockage of the 12-inch-wide opening at the top of the structure, however, prevents the leaking crude from even reaching the riser.
Clearing out the gas hydrates from the cofferdam would simply be a matter of lifting it toward the surface into warmer depths until the crystals melt, Suttles said. The challenge, however, is preventing hydrates from re-forming once the cofferdam is again at the seabed. BP is exploring options for preventing hydrate formation such as heating the structure and adding methanol to the cofferdam's interior to lower the hydrate formation temperature. For now, the cofferdam remains on the seabed away from the leaking well.
Suttles said that other possibilities for controlling the source of flow and stopping the flow altogether include injecting ground-up materials into the bottom of the existing blowout preventer (BOP) in an effort to plug up the device and the well. A risk of using this "junk shot" method, however, is that it could result in an even greater volume of crude being released from the top of the BOP. Another option that is being evaluated is whether to place a second BOP or a similar valve atop the existing BOP to stop the flow of crude. Suttles noted that BP needs to evaluate additional data to determine the viability of these approaches.
Relief Well Progress
Suttles also noted that drilling of the first relief is running ahead of schedule and reached 9,000 feet Saturday. Two relief wells will be drilled to intersect the original wellbore above the oil reservoir; the idea is to pump heavy fluid into the well to stop the flow of oil from the reservoir and then pump cement down to permanently seal the well. The relief wells will intersect the wellbore at a target depth of approximately 18,000 feet.
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