I think he's upset cuz he can't measure the flow, so the leak can't be stopped cuz we don't know the flow, and that it might be 100,000BPD (cuz he doesn't know that would be the largest well in the Gulf)...I think. So I can help him out; AC won't like this, tho, cuz it doesn't fit his story line.
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 |
