BP sends relief rigs back to Macondo - Jul 27, 2010

Rigs drilling the relief wells that will ultimately kill the Macondo blowout in the US Gulf of Mexico are returning to the location after Tropical Storm Bonnie weakened. Thad Allen, head of the US response said it would take between 24 and 36 hours for the rigs to return. On Friday Transocean semi-submersible rigs Development Driller 2 and Development Driller 3 moved out ahead of what was forecast to be heavy seas and winds greater than 40 miles per hour. But waves on the location were only 3 feet to 5 feet on Saturday and were not expected to grow significantly, according to federal officials.

Forecasters with the National Weather Service have officially downgraded Bonnie back to a tropical depression. Support vessels for the remote operated vehicles that monitor the capped well never had to leave, Allen said. Those vessels have a higher tolerance for rough seas. The federal government decided Thursday that they were confident enough to leave the capping stack closed and unattended while the storm passed after more than a week of pressure testing. “We have confidence over the last six days of testing - including searching down and clarifying the anomalies that have been detected - that we are convinced that there’s enough well integrity right now that would allow us with a good basis for confidence that we could leave the well cap over the passage of this storm and return as quickly as possible,” Allen said.

Pressure in the well currently at more than 6860 pounds per square inch and increasing at a little less than 1 psi per hour on Friday. It will take about a week to resume drilling activity, Allen said. “So they would have to reconnect the riser pipe, reconnect the drill string and then go back and remove the [storm packer] that’s in the, you know the well bore.” Development Driller 3, which is drilling the first relief well, had been due to begin setting casing on the first relief well Wednesday. But the crew instead placed a storm packer in the well bore about 300 feet below the blowout preventer.

The rig is at 17,864 feet and has another 100 feet to drill vertically before it will intercept Macondo, which is 4 feet away horisontally. The casing job, including subsequent cementing, was expected to take two to four days and BP did not feel comfortable starting the job with the storm looming. After casing, BP will be ready to begin the first phase of the kill operations.BP got approval to move ahead with plans for a static top kill Thursday.

The UK supermajor still will need a final federal OK before it starts the procedure, which could be significantly delayed by the storm, but it is beginning preparations on shore. Under the rough plan, BP would use the existing subsea manifold that is connected to the choke and kill lines of the original Macondo blowout preventer to pump heavy drilling mud down the well. The mud would push against the flow of oil until it reached the reservoir. Because of the low pressure and the closed system, crews would not have to pump at as high rates and pressures as they did during the first attempt, Wells said.

The first top kill bid was unsuccessful last month when, because of holes in the blowout preventer that allowed mud to escape, BP could not pump enough mud down the bore to overcome the upward pressure of the oil flow. The static kill could be done over the course of about 24 hours, Wells said. Wells has said the bottom kill through the relief well bore would take anywhere from a few days to a few weeks, because BP does not know exactly how oil is traveling up the well. To perform a bottom kill, BP will have to drill into the annulus of the well and if oil is flowing through it, will need to circulate mud to kill the flow and cement it. Then, the crew will have to drill into the casing, and repeat the process if oil is flowing there as well. The top kill could take care of one, or both of those flow paths, Wells said.

Source: www.upstreamonline.com
Date: July 2010