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Environment

Factbox: How BP's static kill works

HOUSTON (Reuters) - BP Plc began a “static kill” of its ruptured Gulf of Mexico oil well on Tuesday, starting the process of killing the leak for good.

BP had said the procedure could be finished in a day, but retired Coast Guard Admiral Thad Allen, the top U.S. official overseeing the spill response, said it could take 33 to 61 hours.

And both say that even if the static kill shows signs of having killed the leak, a relief well will bore into the blown-out Macondo well to either finish the job or make sure it’s done.

Here is an explanation of the static kill and BP’s next steps, according to Allen and Kent Wells, BP’s senior vice president of exploration and production:

THE STATIC KILL:

* The static kill involves pumping drilling mud into the well from surface vessels through pipes and hoses connected to a failed blowout preventer at the seabed.

* The procedure is the same as BP’s failed top kill in May except that the well is capped and sealed, so the mud cannot shoot out the top as it did with the top kill.

* The timeline varies because of where the mud may need to go.

* If oil is found only in the casing, or the pipe that contains a drillpipe and holds the wellbore open, the static kill could wrap up quickly.

* If oil also is found in the drillpipe or in the annulus, the space between the casing and the strata that is usually filled with cement, the procedure could take longer.

* Slowly declining well pressure that now exceeds 6,900 pounds per square inch throughout the static kill will indicate the mud is pushing oil back to the reservoir as hoped.

* Falling or flat pressure could signal a breach in the casing or wellbore that allows mud, oil and gas to leak out the sides.

* Pressure readings in the first five to six hours of the static kill should indicate where the mud is going and signal any problems.

* Once all mud is pumped as needed, BP and U.S. government will decide whether to pump in cement from the top or wait and pump it in from the bottom through a relief well.

* Either way, a relief well will bore into the annulus and possibly the casing to ensure the leak is plugged and pump in mud and cement if necessary.

THE RELIEF WELLS

* By August 2 BP had inserted and cemented in place the last 2,000 feet of casing in the first of two relief wells.

* Drilling is on hold until the static kill is finished.

* The relief well has drilled 12,864 feet beneath the seabed and has another 100 feet to go before initially intercepting the Macondo well.

* The initial intercept of the annulus is on target for August 11-15.

* The relief well’s work could last a few days to the end of August.

* The finish date depends on how well the static kill works, how deep the relief well must bore into the stricken well, and how many times BP must pump in heavy drilling fluid and cement.

* The second relief well, a backup to the first, bored 10,961 feet beneath the seabed by July 12, when drilling was suspended to avoid disturbing the first relief well’s use of sensors to find its intercept target.

WELL PRESSURE

* BP has monitored pressure in the well since it was sealed shut on July 15 for signs of leaks or problems.

* Pressure has slowly risen from 6,700 pounds per square inch on July 16 to 6,989 psi on August 2.

* Rising pressure has indicated that the well remains intact after the April 20 blowout. Lower or falling pressure would be a sign the well is damaged, allowing oil to leak out the sides and possibly breach the seafloor.

* The sluggish rise in pressure could be a sign that the leak largely depleted the reservoir.

BACKUP OIL-CAPTURE VESSELS

* BP is still assembling a surface oil-capture system of four vessels that can siphon up to 80,000 barrels a day from the wellhead.

* That system is slated to include a rig, the Helix Producer; a well-testing ship, the Toisa Pisces; and two Transocean Ltd. drillships.

* Each would be connected to wellhead equipment via hoses and pipes that allow for a quick disconnect if a hurricane approaches.

* The system remains on tap as a backup if any problems arise with the static kill or the relief wells.

Reporting by Kristen Hays in Houston; Editing by Cynthia Osterman

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