Wednesday, May 26, 2010
Latest Effort to Seal Leaking Oil Well in Gulf: Top Kill Scheduled for Today
BP officials say the company is poised to begin the top kill procedure. However, to say they are cautiously optimistic is an understatement. In fact, it's unclear if the mud being pumped into the well can outrun the flow of oil and gas escaping through the hole. If the data returning topside doesn't satisfy the experts, the effort will be aborted. The concern is that the procedure could crack the remains of the blow out preventer and make the leak worse.
A surface supply ship, the HOS Centerline, one of the largest of it's kind in the world, is on site and ready to start pumping mud down the pipe and into the well. This ship has a 30,000 hp engine driving a pump that can deliver 40 to 50 barrels of mud a minute. The problem is: this mud has to overcome the force of the expanding gas and oil coming out of the well at 5,000 feet below sea level. If we assume the initial leak estimate of 5,000 bpd, we're talking about overcoming a flow rate of only 3.5 bpm. But, if, as most people now conclude, the estimate of the leak is much greater, perhaps 20 times greater, then the mud being pumped down will have to overcome as much 69 bpm of gas and oil headed in the opposite direction.
It's not just the well pressure of this gas and oil at depth that they're fighting. It's also the fact that the gas and oil and other material at 5,000 feet below sea level is losing density and gaining momentum as it rises from depth. At 5,000 ft below sea level, the pressure is 148 atmospheres or 2182 psi. As the gas rises, it expands and picks up speed. In order to slow it down, you need to increase its density or increase the hydrostatic pressure against it. To do this during a drilling operation, oil companies use drilling mud, which has a density greater than seawater and greater than the mud in your back yard. Seawater weighs about 8.5 lbs/gal. Drilling mud can weigh as much as 20 lbs/gal.
So, will 40 to 50 bpm of drilling mud being pumped down the 4" repair pipe increase the density of the gas and oil being forced up the pipe? At the same time, will the top kill fluid equal or exceed the hydrostatic pressure of the expanding oil and gas coming up the pipe? But this is just in the pipe. This 4" dia. repair pipe is stuffed in a 21" diameter larger pipe, which itself is stuffed into a broken or compromised blowout preventer. Once the mud flows into the blowout preventer and the top of the well, engineers are hoping the density of the drilling mud will increase the density of the gas and oil enough for them to start to pump cement into the well.
The big risk, of course, is that all this additional pressure will further compromise the remaining structure on the bottom and make everything 100 times worse.