- by BK Lim (17 April 2011)
One year after the Macondo Blowout on 20 April 2010, lingering questions remain on the quantity of the oil spilled. Naturally BP would want to keep the quantity as small as possible to the point of ludicrousness. Even the term used is an understatement. It was in reality a mega oil spew. The term “Spill” had been hotly contested but since BP controlled the airwaves and media, the grossly understated term “spill” stuck. We use the term Spill to mean Spew interchangeably in keeping with the wide miss-use.
Most experts suspected MMS and BP grossly under-estimated the amount of oil spilled. Recent emails exposé suggested BP officials tried to take control of a $500m fund pledged by BP for independent research into the consequences of the Gulf of Mexico oil disaster, according to a report by Guardian, UK. Actions speak louder than words.
Those concerns go far beyond academic interest into the impact of the spill. BP faces billions in fines and penalties, and possible criminal charges arising from the disaster. Its total liability will depend in part on a final account produced by scientists on how much oil entered the gulf from its blown-out well, and the damage done to marine life and coastal areas in Louisiana, Mississippi and Alabama. The oil company disputes the government estimate that 4.1m barrels of oil entered the gulf.
Central to the issue has been the thickness of the oil slick. The area of the oil slick can be estimated from satellite images and aerial photographs, but the thickness remains an unresolved quantity. Although BP had both the capability and technology to measure or sample the thicknesses of the slick at that time, many suspected it was not in the interest of BP to do so; preferring to use the MMS table Notice the number of qualifications made in using the guide. The “greater than” (>) symbol suggests the values given are the minimum.
Remote Sensing & Surveillance of Oil Spills (adapted from CONCAWE: A Field Guide To The Application Of Dispersant To Oil Spills.
An estimate of the quantity of oil observed at sea is crucial. Observers are generally able to distinguish between sheen and thicker patches of oil. However gauging the oil thickness and coverage is rarely easy and is made more difficult if the sea is rough. All such estimates should be viewed with considerable caution. The table below gives some guidance. Most difficult to assess are water-in-oil emulsions and viscous oils like heavy crude and fuel oil, which can vary in thickness from millimeters to several centimeters.
Although much of the observed slick seen in the Macondo Mega Oil spill are orange to black, most estimates used 1 to 2 microns as the average thickness of the sheen. According to the table, the minimum thickness for Brown to Black is 100 microns or 0.1 mm. It seemed quite obvious for BP to use the minimum end of the spectrum rather than the realistic value. Assuming 100 microns, the amount spilled would have been 24.4 million barrels (1.026 billion gallons) on day 34 with 50% void factor in the slick. By comparison at 2 microns, the oil spilled would amount to only 488,744 barrels or 20.5 million gallons on day 34. Even using the minimum 100 microns thickness for “Crude and Fuel Oil” we already see a 50-fold increase in the total estimate. Most independent observers agree it is more than 100 microns.
Assuming the rate of discharge had stablised, a 2-micron thickness would amount to only 1.95 million barrels (82.1 million gallons) of oil by 20th August (approx 4 months). That is why BP is disputing even the modest estimate of 4.1 million barrels (172 million gallons). Assuming 100 microns as the minimum thickness, it would mean more than 370,000 barrels were spewed daily. But not only through one well. In fact more oil were spewed through the numerous fault fractures and vents at the edges of the salt domes as the late Matt Simmons had asserted before his untimely death. BP reluctantly increased the spew rate from 1,000 barrels per day to 5,000 barrels per day, under intense public pressure. Honestly, could a technologically advanced giant like BP make such an innocent blunder as under-estimating the spew rate by as much as 74 times (at 100 microns thickness)? Certainly, it was not an accidental blunder.
Did Matt Simmons have the critical inside information to substantiate a much larger rate of oil spew? Nine months after his death, Matt Simmons could be proven right after all. This article examines some of the critical factors that refute the ridiculous “microns thickness” of the Macondo oil slick.
According to Dr Ian MacDonald (Gulf-oil-spill-rate-must-be-much-higher). The CONCAWE guidelines used by MMS date back to the eighties. The idea that a layer of oil on water will spread until it is only one or two molecules thick dates to Lord Rayleigh in the 1890s. He performed an experiment where he allowed a small drop of oil to spread in a tank. When it reached its maximum extent, he correctly surmised that the layer was ~1 molecule thick. However, he could not SEE the oil; instead he inferred the extent of the layer by floating camphor power on the water. And he got a number of 0.01 micron.
This is NOT what is happening offshore Louisiana. The open ocean is obviously not a laboratory tank. Visible oil layers have to be at LEAST 1 micron thick--even then you are not seeing the oil, just the reflection of light off the layer. An oil layer with a rainbow sheen is ~10 micron thick. Oil with red or brown color is several times thicker than that. Unfortunately this is exactly what we are seeing across much of the Deep Horizon spill. Misstating the thickness of the main sheen by a factor of 1000 has a direct effect of reducing the estimates of spill magnitude. The point is, even at 10 micron these are still not thick layers. They are 1/10th the thickness of a human hair, but they cover enormous areas. The areas add up to a very large volume of drifting oil.
Brian Grote (BP director) made a misleading statement that has been repeated. He said that the "wider sheen, has a thickness of one or two hydrocarbon molecules" (as quoted in Upstream Online http://www.upstreamonline.com/live/article213244.ece?WT.mc_id=rechargenews_rss).
APRIL 28, 2010 10:48 AM
CONCAWE was established in 1963 by a small group of leading oil companies to carry out research on environmental issues relevant to the oil industry. Our membership has broadened to include most oil companies operating in Europe. The scope of CONCAWE’s activities has gradually expanded in line with the development of societal concerns over environmental, health and safety issues. Our research now covers areas such as fuels quality and emissions, air quality, water quality, soil contamination, waste, occupational health and safety, petroleum product stewardship and cross-country pipeline performance.
The CONCAWE guidelines were set up by the oil companies for the oil companies since they would be the only ones causing the spills. This itself raises the question of objectivity. Oil companies are not non-profit organization and they are staffed with top-of-the-food-chain predators in the dog-eat-dog business world. This is evident from the compensation scheme to the gulf victims and businesses suffered as a result of the oil spill. They give an inch for a foot. Don't wish for them to be Santa Clauses. They are not. Can you trust them to use the table objectively? The answer is NO.
As commented by Dr Ian and most independent observers, the slick is more black and brown than light Iridescent (rainbow). Most would agree that at least 100 microns or 0.1mm should be the starting point of any estimation; not 1 micron or 0.0001mm. By common logic, if you cannot see a single strand of hair (and a micron is 1/20 to 1/180 the thickness of a single strand of hair) from a distance of 1 m, you are not going to see a 1 micron thick sheen (a couple of molecules thick) covering even 1 sq mile in the open sea, assuming you can stretch the oil film that thin without the oil molecules breaking up into smaller “dollar coin” size patches.
So for a director of the world's largest oil company to say that a few molecules thick of oil film can cover up to 30,000 sq miles in open choppy seas with winds causing ripples, is it not stretching the “dollar” a bit too far and wide? Figure 14 of the Real-time Detection of Oil Slick Thickness Patterns with a Portable Multispectral Sensor shows how 7 – 10 microns sheen looks like in a controlled lab pool. Hardly perceptible if the writers had not marked it with red arrows. This report was published by MMS in July 2006.
By logic and experience at sea, the majority of the oil slick area shown in the satellite images are more than 100 microns (minimum thickness on the table used by MMS and BP) but nobody dared to venture beyond that for many reasons. The fear of assassination where billions of dollars are at stake is real. More than 9 deaths linked to the BP gulf causes cannot be accidental.
Most laboratory experiments use scaled down models and none had been field-tested in an open sea. Having minimum values is fine but where is the upper limit? There is a good vested-interest reason for not giving an upper limit. In any legal tussle, the average of the maximum and minimum would be deemed fair but disastrous to the oil spill offender. Say if the upper limit is capped at 1 inch or 25.4 mm. The mean value of 100 and 25,400 microns is 12,750 microns. This will practically bankrupt BP or any company causing the spill.
Satellite imaging like all visual techniques suffer from the effect of illusion and scaling factor. In my earlier articles,I had commented that if common logic and scientific reasoning had taken precedent over visual illusion, Europe and the air travel industry would have saved more than 2 billion Euros of losses. Millions around the world not have been greatly inconvenienced by the Total Airspace Ban and the economic costs affected by the ban during the Iceland volcanic eruption episode. This illustrates that geohazards geophysics is not all about disaster prevention but can be an effective decision-making tool that makes economic sense on a larger scale. The Macondo wells would have shifted to a safe drilling location if professional (not subservient) geohazards geophysical principles had been applied. Similarly, if the early recovery efforts had followed the proper guiding principles based on predictive analysis we would not be caught in a congested highway heading to “a beyond patch-up” destination (Why-is-BP's blowout-so-disastrous-beyond-patch-up).
All maps and images have a “focus range” like in camera images. If the scale or colour range is adjusted to see all, then you cannot see the minute details. Say on a 0 to 100 scale, your major contour lines would typically be a multiple of ten with intervals of 1 unit. Forget about seeing details or variations as small as 1 or 2 decimal places. This is putting perspective in numbers.
So if we want to see molecular size thickness of the slick we have to zoom in million of times since the slick area is more than 30,000 sq miles. We don't have to be rocket scientists to see if the BP director is talking through his ….... ! Even if we can by some super-duper technology, cramp all the information into the satellite images, our eyes or any visualization programmes will be over-saturated by the high intensity values. I am not saying molecular thickness sheen (1 micron) do not exist. They do but are “not visible” to us in the presence of inch-thick oil layers. In all probability the dark core of the oil slick in the satellite images are the thicker oil layers while the “invisible” 1 micron sheen extend several miles beyond the visible limits of the slick.
Equating hundreds of microns to just 2 microns over 30,000 sq miles of the visible, thicker slick is like saying; “where is the oil?” That explained the urgency to aerially spray the dispersant to sink the oil. But images of the oil slick had already been captured and published. Applying the principles of geohazards geophysics and geophysical interpretation, we can re-examine these images to eliminate the improbabilities which of late seem to be the norm rather than the exception. Before we do that in subsequent articles, let us reexamine some fundamental physics and facts.
Average thickness of only a few microns? Even 100 microns thickness is an understatement.
In one model study Oil Spill Drift & Fate model the rate of decreasing oil thickness was computed to be 0.0056 mm per hour. Ecoceane recorded a rate of 0.051 mm per hour from 5000 tons (approx 35,000 barrels) of oil spreading over 545 hectares in 96 hours. This was 10 times faster than the model study. This is not surprising given the number of factors that could affect the spreading rate. Bear in mind most oil spill studies are based on fixed quantity leaking source at water level. In contrast, a conservative estimate of the Macondo Oil Spew is already 4.1 million barrels (172 million gallons). The Macondo Oil Spew is quite different from any previous oil spills. Some factors that invariably increase the thickness of the oil slick are:
- the enormous quantity of oil and gas spewed and the rate of spew. If the spreading rate cannot accommodate the spew rate, thickness builds up at the source area.
- the enormous water depth (5000ft) of the multiple leaks. In the long ascent to the surface, the effect of gas aeration and turbulence of spew with drastic decrease in pressure will hasten the emulsification (sea water droplets suspended in oil) process and increases the viscosity and volume. The lighter hydrocarbon will separate from the heavier stew. The deeper the source the larger the area of the slick, prior to spreading.
- evidences suggest not a single well spew but several spewing sources over a 7 sq miles area. It is like having simultaneous multiple spews. The net effect would be an increase in slick thickness. The Exxon Valdez is a single source leak, not a spew.
- the enormous surface area of the oil slick (30,000 sq miles on day 34). Like a traffic jam in a mass exodus, resistance builds in the spreading as the area gets larger. Without the supply of new oil, the slick would have broken up into numerous smaller slicks. The fact that the slick area seemed contiguous suggest thicker not thinner (as in the thinnest possible). Without stopping the spewing sources, the surface area of slick is proportionally related to the thickness of the slick, minus the thinning-spreading factor.
- the length of spew (at least 85 days). The peak spew will coincide with peak rate of spreading area.
In the Ecoceane example, the spreading rate was estimated to be only 5 hectares per hour while the average recorded growth rate at the Macondo Oil Spill was almost 12,000 hectares per hour. Unlike fixed quantity source spill, the spreading area rate is also affected by the supply rate and new sources of leaks. If the spreading rate is slower than the supply rate of new oil, the oil slick thickness may actually increase.
Clearly we are seeing an oil slick of a totally different dimension and nature. Thus, can the simple experiment performed by Lord Rayleigh in the 1890s where a small drop of oil was allowed to spread in a tank, be truly applicable in the Macondo Mega oil spill? If not, why then did BP and MMS still use his experimental data as the basis of estimating the volume of the spew? If the Macondo Mega oil spew is at least a million times bigger than Lord Rayleigh's “small drop of oil” does it make sense to use the lowest minimum of a few molecular thickness as the basis for estimating the average thickness of the oil slick and thus the total volume of oil spewed? The evidences given here make a mockery out of the perceived microns slick thickness. The minimum value for the brown – black oil slick is 100 microns. Some quantitative direct estimation of oil slick thicknesses are possible using photo images either from sea level, aerial reconnaissance or satellites.
An increase in viscosity will invariably contribute (positively) to the thickness of the floating fluid layer due to surface tension. In calm sea state, we can see convex advancing front of the slick. The radius of the curvature of the advancing front bears a certain relationship to the thickness of the floating layer. If this can be observed from the airplane, the thickness of the slick can never be a few microns. It is only after the surface tension has broken down, the oil starts to diffuse into elongated linear pattern. See the similarities in the slick pattern of both the model study (figure 14) and the satellite image (figure 15, ENVISAT satellite SAR) acquired on 17 Nov 2002 showing the slick from the leaking tanker Prestige off Spain.
For any given oil spew, an increase in the water depth will diminish the power to force the oil slick away from the source point. Imagine a high pressure hose injecting oil from beneath the water surface. If the nozzle is close to the water surface, the oil may even form a vertical column of fountain and the converted lateral force is clearly evident from the ripples radiating from the source. Lowering the nozzle will reduced the amplitude of the radiating ripples with a wider spread. Lower the nozzle even deeper, there will be a point where the ripples may not be even perceptible but replaced with more gentle bubbling over an even wider circle. If the Macondo oil Spew had occurred in much shallower water, the converted lateral force would have pushed the slick into a faster spreading rate. At 5000 ft, this force in area-spreading is negligible. Thus the thicknesses of the oil slick had to be much larger than the lab models with the minimum oil thicknesses.
When the spew rate is higher than the spreading rate (with respect to volume) the slick thickness can never be uniform. The thickness generally decreases from the source point (a few inches?) to the visual limit (100 micron?, seen from aerial photos and satellite images) and from there onwards a wider margin of a couple of micron thick sheen. This applies to an unbroken area of slick. Once a patch of slick breaks off from the main slick, the thickness is governed by other factors. Needless to say, when a broken patch of oil drifts to the shore, the thickness and area size would have decreased considerably. It is thus a fallacy that the oil slick is thicker close to shore than far offshore in the open sea where the oil slick originated. The reverse is true. The thickness of the oil slick near shore is like the clinical thermometer; it is at the very least, as thick as the outer peripheral of the main slick it broke off from. Likewise the thickness of the oil covering the birds and other marine animals, is in the same order of thickness of the oil slick that overwhelmed them. The birds (especially) did not swim around “corralling” or accumulating layers of micron-thick oil on their feathers. If the slick had been only a few microns thick, would the large birds like cranes be stuck to the gluey slick. In some pictures, the birds could not even break free the thick strands of gluey oil even a couple of feet above the slick. Honestly, it does not take a rocket scientist to figure the oil slick to be much thicker than a few mm. So 1 inch thick slick is not so far fetch at the source of the oil spew.
In conclusion, the CONCAWE guidelines were largely designed for limited oil spills from tankers and shallow water wells; not for an unprecedented mega oil spill, spewing uncontrollably from a deep water well (>5000ft) and multiple fractures and vents within a 7 mile radius. Obviously the deep water depth had a great effect on the thickness of the slick. By the time the oil reached the sea surface, it had spread over a much larger area and had lost the “jetting power of a geyser” to force the slick away from the source. Being more gentle and widespread, the floating oil accumulated in thickness with little force to radiate outwards. The relatively calm weather in the first few weeks was also an accumulating factor.
Don't take my word for it. Look at the photo evidence and interpretation in the following postings and see if logic and the truth prevails. Even the government's estimate of 4.1 million barrels (172 million gallons) is a gross misjudgment of the facts and publicly available information. Should BP be allowed to discount further on this grossly under-estimated volume of oil spewed?