I was talking to a friend of mine today who knows about pumps and asked him what he reckoned the velocity of the BP blow out to be from the video feed. He guessed about 3 km/hour (1.88 mph). (In these sorts of things, I value opinions from practical guys – I don’t think that you need to be a professor of fluid mechanics to guess at flow velocities.)
Let’s assume that his guess is right within an order of magnitude/ The diameter of the riser pipe is apparently 21 inches =21*.0254 m= 0.5334 m. The volume of the blow out would therefore be: 3000 (m/hr) *pi *( 0.5334/2)^2 = 670.374 m^3/hour = 670,374 liters/hour.
One bbl oil = 158.987 liters. Thus 670,374/158.987 = 4216 barrels/hour
I.e. 101,184 barrels/day. (Phil Worley of Purdue estimated 70,000 bbl/day.
In order to get 5,000 barrels/day, you would have to have a discharge velocity of 0.1 mph instead of my friend’s guess of 2 mph or a smaller effective pipe diameter. [See update below as this latter seems to be the case, though not down to 5,000 bbl/day. Looks like 15-20,000 is more probable.]
I wonder how they arrived at their estimate of 5,000 barrels/day. Maybe their Group Vice President, Research and Engineering should have spent more time trying to figure this out and less trying to hide the trick to hide the decline.
Update – good news. It appears that the “top kill” was successful and the blow out is sealed. The article contained new estimates of discharge rates by the US Geological Survey about 3-4 times higher than BP’s, but not 10-20 times higher:
Marcia McNutt, the director of the US Geological Survey, estimated that the flow ranged from 12,000 to 19,000 barrels per day.
Up to now, BP estimated the leak at 5,000 barrels (210,000 gallons) per day, but has said that figure is unreliable.
Update: Re-doing these calculations with suggestions made by readers – 9 7/8″ pipe and 50% gas and the same discharge velocity (3 km/hour) yields a bit over 11,000 bbl/day.
Pipe area is pi *(0.250825/2)^2 # 0.0494119 m^2
Volume discharge is 0.0494119* 3000 # 148.2357 m^3/hour
i.e. 148.2357 *1000 /158.987 #932.3762 #bbl/hour
Oil discharge is 24 hours *932.3762 bbl/hour *.5 # 11188.51 bbl/day
Update June 16 – here current estimates are about 60,000 bbl/day