Watch. People think the flow was a square wave. It was an ascending ramp.
Summary – My best estimates is that the current leak rate is about 25,000 bpd in a range between 20,000 and 35,000 bpd.
But the total spilled oil is not the 1,200,000 barrels (900,000 to 1,800,000 barrel range) that the media would get by multiplying the rate times the number of days. It is probably considerably less, maybe about 620,000 barrels (300,000 and 1,000,000 barrel range). This is allowing for about 50,000 barrels recovered and at least 90% of the oil prior to the DWH sinking being burned off.
Why the difference? And my convoluted way of getting there.
One of the things that most people seem to miss is that the leak through the BOP has been growing with time.
The original estimate by the government a couple days after the DWH sank was 1,000 bpd based on the size of the oil slick. At this time the slick was small and they weren’t using subsea dispersants.
About 4 days later (Apr 28) they increased that to 5,000 bpd also based on the size of the slick.
I have no reason to believe these estimates weren’t reasonable at the time although there was probably oil being absorbed into the water column that wasn’t being accounted for.
Estimating from oil spills gets more difficult as the spill get larger, the oil breaks into separated strands and dispersants are added. Oil slicks, like mixed phase, turbulent flow is very difficult to gauge accurately. Error rates in the range of +/- 50% are common.
The next estimate was based on a May 11 video of the end of the broken riser released by BP. Professor Wereley of Purdue who estimate 72,179 bpd from the riser and threw in 25,000 from the kink in the riser for a total of over 97,000 bpd. He presented this to the media and on May 19 to a Congressional committee. They made his work public and it was full of errors. I won’t keep beating that dead horse but I wrote some previous comments about his errors. But using his particle velocity measurements (that is his field of expertise) I came up with a range of 8,000 to 24,000 bpd – 16,000 bpd (+/-50%)..
The task force has estimate 12,000 to 19,000 bpd, but they also had one group saying up to 25,000 bpd. We don’t know the date of the spill information or video clips they used. I’m not comfortable with the 12,000 to 19,000 range as that is inside the error range I think is reasonable considering the quality of the data. I’ll go with the 12,000 to 25,000 range.
When BP cut off the riser they estimated an increase of 20%.
Those are the data points we have to work from – very poor and lots of unknowns.
We know from the pressure readings at the BOP that there was a restriction through the BOP that dropped the pressure by 5,000 to 6,000 psi. There was also a pressure drop across the kink.
It was visually apparent that the leak at the kink dramatically increased from nothing in early pictures to a couple small leaks a few days later to about 4 or 5 sizable leaks before BP cut off the riser so we know there is a considerable increase due to erosion.
I tried to make a rough graph of the increase of flow rate over time with this very poor data but it suggests a logarithmic curve with a very high rate of increase in the beginning which decreases with time. This would seem to support some common sense factors. Erosion of the leaks will drop as the volume of the leak gets larger in relation “circumference” of the holes, the driving pressure will drop as the volume increases and there might be a drop in formation pressure.
Taking a wild guess it appears that the increase from the task force report until the date of cutting the riser could be in the order of 10%.
If we try to compile this we get a time line like this:
April 23 – 1,000 bpd (+/-50%) – US government from spill
April 28 – 5,000 bpd (+/-50%) - US government from spill
May 11 – 16,000 bpd (+/-50%) – Wereley modified by me
May 20? - 18,500 bpd (+/- 35%) - task force (date of data unknown)
June 5 – 21,000 bpd (+/-40%) – before risers cut based on log curve growth
June 5 – 25,000 bpd (+/-40%) - after riser cut based on BP’s 20% increase
Because BP is recovering 15,000 bpd and there is still flow through 2 or 3 relief valves that appear to be about 4” dia plus some leakage at the bottom of the cap I feel safe in putting the bottom limit at 20,000 bpd.
And I think the flow rate is probably close to or at its maximum barring any additional damage to the plumbing. Further erosion will probably be offset by decreases in formation pressure.
By the way, BP has never made a public estimate of the flow, every time the media attributed a flow rate to BP it was actually from NOAA or the USCG. That was confirmed by Admiral Allen on Monday.
shelburn on June 8, 2010 - 3:46pm
theoildrum.com
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theoildrum.com
SHELBURN on June 18, 2010 - 12:45pm
For the most part I agree with your assessment of the legal aspects but BP has no commercial interest in the spilled oil except for their liability associated with it. There is very little value to the oil that has spilled.
10 days ago I did a quick engineering study about the rate of the leak and the growth due to erosion - very rough figures but much more scientifically supportable than the hyperbole being spread by the media.
theoildrum.com
Since then I saw the high res shots of the riser after it was cut and it is clear there is a large stream from the drill pipe which might not have been leaking at all before. So I think the increase in leakage when they cut the riser might have been closer to 50%, not the 20% BP suggested. My new estimate after June 5th is in the range of 30,000 to 45,000 bpd.
By the way, in line with your legal theories, BP never made any flow estimates. All official estimates came from government entities plus a whole lot from instant experts on MSM.
If you take a reasonable flow rate over the life of the leak as it increased from about 2,000 bpd to 35,000 bpd the total leaking from the BOP is probably more than 700,000 bbl and less than 1,600,000 bbl (30 to 70 million gallons).
So for this exercise lets assume 1,200,000 bbl has leaked out the BOP, remembering these numbers may be higher or lower by 40%+.
600,000 bbl (50%) has evaporated or dispersed, could be more but 50% seems reasonable.
125,000 bbl has been burned at sea - this is the USCG's estimate and could be way off.
100,000 bbl has been recovered by skimmers based on 20% of the USCG reported 21.9 million gallons of oily water.
200,000 bbl has been captured - this is a pretty exact number and can be found on a spreadsheet at energy.gov
5,000 bbl has been burned on the Q4000.
That leaves about 170,000 bbl unaccounted for - floating around in spills, on the shore, in the marshes, etc.
And before I am attacked about the size of the spills - try to watch some of the aerial shots when they pan away from the large collection of emulsion. It is difficult as the media wants to show the worst of it but there are large areas of open water filled with streaks of oil and emulsion. I would wager that if you did an detailed aerial survey about 70% to 90% of the area reported as slicks actually consists of open water. It is one of the reasons it is so hard to clean up, most skimmers are designed to clean up coherent slicks, the thicker the better.
Back to the value to BP. The amount that is burned and evaporated has become air pollution, distributed over a large volume of atmosphere so its effect is greatly reduced.
The 100,000 bbl recovered by skimmers probably is weathered enough that very little of it can be recovered except by spending more money, in other words it has a negative value. Even very fresh oil that is skimmed has been exposed to salt water so its commercial value is greatly discounted, maybe about $10 to $20 per barrel at best. The oil still floating is likewise worth little to nothing.
The 200,000 bbl that has been recovered is probably worth about $15,000,000. A portion (12.5%? or 16%?) goes to the government as royalty and BP has said that they are going to donate the rest to a wildlife fund for the Gulf Coast. BP is capturing about 15,000 bpd worth about $1,000,000 a day but their costs of the recovery are probably close to $2,000,000 per day for the Discoverer Enterprise, the Q4000 and all the ROVs and support vessels.
Maybe you could find the legal document that sets up the wildlife fund and determine if it is actually above and beyond or if it just offsets cost that BP is liable for anyway. |
