Accidents involving petroleum and natural gas extraction, transportation, or processing are frequent enough to be of major concern to environmentalists. Oil spills on land, where most oil wells are located, usually can be stopped quickly. Most spillage is confined to the site immediately around the wellhead. The area may appear "messy" for awhile but the damaged environment can eventually be cleaned up.
A much more dreaded oil spill is one that contaminates the ocean from a failure at an offshore drilling site, from tanker accidents, or from submarine pipelines. Such events are not uncommon and some can be catastrophic. Fortunately, such spills can be easily monitored from ships, the air, and from orbiting spacecraft. For ocean spills, in particular, remote sensing data can provide information on the rate and direction of oil movement through multi-temporal imaging, and input to drift prediction modelling and may facilitate in targeting clean-up and control efforts. Remote sensing devices used include the use of infrared video and photography from airborne platforms, thermal infrared imaging, airborne laser fluourosensors, airborne and space-borne optical sensors, as well as airborne and spaceborne SAR. Oil is noted for "calming the waters", i.e., reducing the degree of wave disturbance, making it visible in certain spectral bands. Multiple oil leaks in the Arabian Sea, west of Bombay, India, are obvious in the SIR-C radar image below. Their darkness is not solely due to black oil color involving light absorption but also to the decreased backscatter of the radar beam (see Section 8 for the principles).
Radar imagery, especially in the black and white mode, is very effective at locating and monitoring oil spills over their full extents. This next image, made by the radar unit on Envisat, shows how radar graphically highlights the large oil spill resulting from the breakup of the oil tanker Prestige in late November, 2002. Most of its cargo of 20 million barrels went down with the ship as it sank into deep waters. But 1.5 million barrels of oil eventually reached the northwest corner of Spain, contaminating almost 300 km (200 miles) of beach. Here is a radar image taken soon after the spill leaked out.
This next image, of an oil spill from a tanker off the west coast of the Korean peninsula, was made by the ASAR instrument on ESA's Envisat:
Surprisingly, Landsat is not the prime satellite used in monitoring oil spills. Images made by Landsat don't usually show up the oil as "contrasty" against a water background. Here is one example that requires some effort to recognize the oil-affected surface; it is a spill from a drilling platform in the Sea of Timor:
Oil can also reach marine surfaces from so-called "oil seeps", which are natural effusions of oil from fractures underlying the ocean floor. Off Santa Barbara (California) is a persistent natural "spill" shown here as an ERS-1 radar image:
Oil is also commonly added to the sea surface as an "acceptable" steady leak from ships that use oil instead of coal as propulsive fuel. This radar image shows oil trails from two ships off the west coast of Italy:
Ultraviolet (UV) radiation is an effective tool for monitoring oil on water because petroleum responds by fluorescing. Various companies now offer oil spill monitoring services. One is Optimare of Denmark. Its website lists these applications of its Imaging Airborne Laser Fluorescence Scanner (IALFS) instrument:
* Detection of laser-induced fluorescence of crude oils, petroleum products and water constituents.
* Classification and mapping of crude oils, petroleum products and chemicals spilled at sea.
* Detection of crude oils, petroleum products and chemicals floating underneath the water surface.
* Measurements of oil film thickness over very thin (optically thin) oil layers.
* Distinction of naturally occurring biogenic slicks from oil spills.
* Hydrographic measurements (CDOM, turbidity, chlorophyll-a).
Here are two images of an oil spill taken first by Optimare's IALFS and then by their IR/UV line scanner instruments:
Infrared detection of oil slicks depends on the fact that oil appears cooler than surrounding water most of the time. Here is a mid-gray patch of oil in the river passing by a refinery in Baytown, TX near Houston:
With the advent of high resolution satellites, much more information is now available over short turnaround times above major oil spills. One occured in the Aleutians off Unalaska in mid-December, 2004. A tanker split in half, leaking 10s of thousands of gallons of crude into offshore waters. The boat wreakage and oil-coated waters were imaged by Quickbird:
Until the BP oil spill of 2010 (see below), the most infamous U.S. oil spill was in 1989 off Prince William Sound on the Alaskan coast. The tanker Exxon Valdez ran aground against a reef and split open. Almost 11 of its 55 million gallons of oil escaped to open waters. Its story is told pictorially in these two photos:
Oddly, this Alaskan oil spill was not well documented by satellite imagery. Most tracking of the migrating oil was done from aircraft and ships.
As seen from the above discussion, oil and other petroleum products can be accidentally introduced into the ocean in several ways. One source is at or below drilling platforms. For the U.S., the most numerous of these is in the western half of the Gulf of Mexico, as shown by this map; as would be expected, relatively few of these are in deep water far out into the Gulf:
At any given time, there is also oil reaching the Gulf surface simply from natural seeps, as shown in these two images:
However, the ever present fear is some kind of catastrophe failure at the drilling platform or on the sea bottom at the well head. What has become the worst oil spill in American history occurred about 50 miles offshore from Louisiana's Mississippi River delta. A drilling platform - known as the Deepwater Horizon. operated by British Petroleum (BP) exploded from a gas leak on April 20, 2010 and sank, killing 11 workers. The causes of the catastrophe are technical, but involve ignition of escaping methane gas; bad safety practices are also a major factor.Here is the platform as it was towed to its final site.
Once at the site, the platform floats freely and its position is maintained using motors called thrusters (fixed propellers). Deepwater Horizon was built in Korea and is operated by Transocean. It can drill in up to 2400 meters (about 8000 feet) of water. At the time of the accident a crew of 115 persons were aboard. Here is a photo of the emplaced platform; below that is a view of the intense fire consuming the platform; it collapsed 36 hours after the initial explosion::
At the time of this event, the drilling, which starts at the ocean floor some 1500 meters (about 5000 ft), had reached a rich reservoir of oil at a depth exceeding 4000 meters (13000 ft). The oil was mixed with natural gas and under high pressure. It flowed readily to the wellhead, thence through pipes to the surface platform. But conditions existed that would lead to failure, full-scale leakage, and an environmental disaster the magnitude of which the U.S. had never experienced before.
Apparently, the Deepwater Horizon well was inadequately sealed, and natural gas built up inside it. This drove both drilling mud and oil itself out onto the ocean floor, initiating the leak. When workers on the rig tried to activate the well�s blowout preventer (BOP), it failed. An attempt to activate the blowout preventer after the fact, using undersea robots, also proved unsuccessful. The oil, driven by the embodied gas, leaked from the well head some 1600 meters below the surface. Hundreds of thousands of barrels of oil came the surface to form a slick that headed towards the Gulf coast. Here are three images of that slick taken a few days into the disaster:
Satellites tracked this oil spill for months. In fact, this is a disaster in which satellite observations (and remote sensing in general) played a primary, pivotal role in monitoring the spill over time and its consequences for the environment. The ability of many satellites with wide fields of view to detect and encompass the entire spill in single images showed clearly their advantage over aerial photography.
For a while, winds kept most of the oil from reaching the Gulf states shores until mid-May. But, a month after the leak began, it still had not been shut off. Tens of thousands of barrels have escaped into various levels of the Gulf waters. One fear is that the Loop current, which begins in the Gulf, swings around the tip of Florida, and then joins the Gulf Stream up the Atlantic coast, will carry the oil beyond the Gulf - greatly extending the damage both to the fishing industry and to tourism. That this may happen is evident from this MODIS image made on May 17th, in which a streamer of oil is moving southward towards the Loop current:
Satellites have followed the growing spill (as of June 1st, about the same areal extent as the state of Connecticut; it grew even larger, exceeding the size of Florida). A series of maps that track the spill's location, size, and shape can be accessed at this CNN website, provided it is still active. While the size keeps enlarging, the shape and coherence changes constantly, even as its location shifts owing to guiding currents and wind effects. Here is an image obtained nearly five weeks after the initial failure; part of the spill appears bright because of sunglint:
The next series of images indicate the diversity of views obtained from different satellites. The first pair shows that, as seems logical, similar sensors produce nearly identical images; a MODIS view is on top of a view made by Envisat's MERIS:
The next pair compares the scene on May 18 as captured by the ASAR radar on Envisat and the MODIS optical instrument on Terra:
Radar is especially effective at imaging oil on water. Here are a Radarsat and a COSMO Sky Med (Italian satellites) image of the Gulf spill:
The "old reliable" Landsat-7 took this image of the spill:
Specialized sensors can enhance the appearance of the oil spill, making it easier to establish boundaries. The MISR (Multi-angle Imaging Spectro-Radiometer) on the Terra spacecraft has produced images like this:
Because of its size, meteorological satellites can easily detect the spill as evidenced in this Eumetsat image. Their wide field of view (FOV) provides a unified look at the entire extent of the spill.
But, smaller FOVs are useful in monitoring parts of the spill that are at or nearing shorelines. This EO-1 ALI image of the coast off the state of Mississippi is a good example:
The high resolution satellites such as IKONOS and Quickbird can see small areas of the spill in detail; this is the case in this Quickbird image:
Digital Globe's WorldView-2 satellite obtained this view:
In between these scales, Terra's ASTER produces images such as this, which shows the oil (rendered here as silver streaks) moving onto the birdsfoot distributaries of the Mississippi River delta:
The land in the distributaries is just above sealevel - low and flat - and thus is easily breached by high waves during a storm. This aerial photo shows that condition:
Humans in space have joined in the observations. An astronaut photo taken from the International Space Station gives a different impression of the spill since it is oblique (visualized on a slant):
Photos taken from airplanes and helicopters allow specific problem areas to be checked out. A small part of the spill is seen in these aerial photos. Note its distinct brownish-red color.
NASA has conducted its own aerial flights over the oil spill, designed to obtain detailed spectral measurements of the properties of the oil as it rests on the Gulf waters. The plane involved is ER-2, a modified U-2 (the famed spy plane used in the Cold War era):
The instrument that gathered the data is AVIRIS (Airborne Visible/Infrared Imaging Spectrometer), described on page 13-9, which is a hyperspectral imaging system as well as one capable of producing a continuous spectral curve. AVIRIS can produce both natural and false color images such as this true color one of the oil streaks within the spill.
Spectral curves for the oil itself have been measured in the Spectroscopy Laboratory of the U.S. Geological Survey in Denver, CO.
Compare that plot with the one produced by the AVIRIS overflight at 28000 feet (~8.5 km).
The AVIRIS data have been used to produce images in false color using individual hyperspectral bands:
The following is a description of these images given in a NASA press release: AVIRIS measures a spectrum of the surface at each pixel from 0.35 to 2.5 microns (the visible spectrum is: blue: 0.4 microns, green 0.53 microns, deep red 0.7 microns) in 224 wavelengths. This fine spectral sampling allows discrimination of absorptions due to specific compounds in the scene. A, a color-infrared composite image in which reflectance at 2.46 microns is assigned the color red, reflectance at 1.6 microns is assigned green, and reflectance at 0.55 microns is assigned blue. B, an image produced by assigning the measured strength of the absorption at 2.3 microns as red, assigning the absorption strength at 1.73 microns to green, and assigning the absorption strength at 1.2 microns to blue. The absorption at 2.3 microns is intrinsically the strongest organic absorption in the oil in this spectral range and is sensitive to thin/small amounts of oil. The absorption at 1.73 microns is sensitive to greater amounts of oil. The absorption at 1.2 microns is weaker and needs the greatest amount of oil to register. For such thick layers of oil, the stronger absorptions are saturated and do not change significantly (as shown in figure on right) leaving the 1.2-micron feature to probe the thickest oil. The image on the left (A) shows the position of the oil well head (marked with a "w"). Pixel spacing is 8.5 meters so each pixel covers about 72 square meters. The images shown cover about 67 square kilometers, and are a subset of a long flight line. Data analysis indicates oil was detected in a total of more than 4 million square meters (more than 57000 pixels) in this scene. Small dots, some of which appear white in A and red or green in B, are boats whose paint reflects light with organic spectral signatures.
Satellites and aircraft are the primary platforms for observing the effects of the spill over the open ocean and along the beaches and coastal wetlands. But the scope of the spill catastrophe has justified some other novel ways of monitoring these effects. A Navy blimp, the MZ-3A, and helicopters, allow observers to remain over small areas at a time, noting details that are immediately relayed back to ground workers engaged in setting up protection barriers or in cleaning up contaminating oil. Here is the blimp and a helicopter, being used in tandem:
A NASA web site summarizes how satellites play(ed) a role in the BP spill monitoring.
To see how the spill's main segments have moved from day to day, click on this CNN website. Note that there are significant variations from one 24-hour period to the next. These changes are due in part to the influence of winds and currents but also due to shortcomings in the satellite detection of boundaries, etc.
Of course, satellites can only see oil at the surface. There have been reports that much oil remains beneath, at various depths, dispersed and also in plumes. The evidence for this is ambiguous but such subsurface distribution is likely, despite oil's tendency to rise through the water.
Now, with this overview of how the BP oil spill has been observed by various remote sensing endeavors, mainly satellite observations, let us examine in some detail the ecological results of the spill and then the efforts that have been made to stop or at least contain the spill at the wellhead, in part by capturing some of the escaping oil and bringing it to ships at the surface. This was the first failure of an oil well in deep water. That depth, nearly a mile, has made it extremely difficult to cap or otherwise contain the escaping oil. Remote cameras from nearby submersibles capture the gushing oil at the wellhead:
Many Internet sites posted live pictures of the oil gushing from the wellhead. Here is one such site that should work:YouTube.
The oil appears dark, almost blackish as seen underwater. In sunlight it has a reddish overtone, as visible on a worker's hand in this photo:
By mid-May, oil had now reached en masse the fragile wetlands of the Louisiana and Mississippi coasts, as exemplified here:
The effects of the spill on both the marine and the coastal ecosystems has been devastating (but this is generally true for most such spills). This is brought home by this photo of an oil-covered Brown Pelican - the state bird of Louisiana:
Hundreds of pelicans have been retrieved, cleaned up, and released elsewhere in Florida and Texas. But many are not being found and are presumed to have died. Oil-drenched pelicans cannot fly off the water:
Among marine animals seriously affected by the oil are several species of endangered sea turles:
The deaths of turtles, dolphins, birds, and many marsh dwellers is evident in this image (but keep in mind that fish and countless smaller marine organisms have died as well):
One of the most dire consequences of the spill has been its impact on the fishing industry. Especially vulnerable are the tuna, the shrimp, and the oyster beds. Louisiana is the largest supplier of oysters in the U.S. The oyster industry, some firms more than 130 years in business, has been financially devastated. Here is an example of a compromised oyster.
Crabs, another mainstay of the Gulf seafood industry, is also much affected.
Dead fish are washing up on shore. Some are covered with oil, as seen below. But did the oil itself kill the fish. Post mortems suggest yes, in some cases. But not always: other factors may be involved and the oil is just a coincidental coating.
The BP spill is now judged to be the worst petroleum drilling disaster in American history. It has closed fishing and shrimping in a large part of the northern Gulf of Mexico and is inhibiting tourism. Its price tag will eventually exceed tens of billions.
The amount of oil that has leaked so far has proved hard to estimate. BP originally said that 5000 barrels (one barrel contains 42 gallons) come out each day. Others believe the amount is (much) higher (that has been confirmed; see second paragraph below). For the lower estimate, this yields about 7.9 million gallons in the first 35 days. However, as time progressed and better observations of the gushing at the wellhead led to more exacting calculations, the dailing spill size estimate kept rising, first to between 11000 and 19000 barrels, then 25000 barrels, then 35000 barrels, and thereafter to between 40000 and 60000 barrels (a few claim even more).
Until 2010, the largest spill in the western hemisphere was in the Gulf of Mexico off the Mexican coast. The Ixtoc drill platform, operated by Pemex, in the Bay of Campeche off the Yucatan had a blowout failure that released 138 million gallons of oil over a 10 month period (time needed to finally shut it off) between June of 1979 and March of 1980 (see photo below). The oil drifted northward and eventually produced moderate contamination of the Texas coast. But in time its initial ecological impact has lessened to the now almost nil traces of damage. Most of the oil stayed at sea and was gradually destroyed by a combination of dispersants and petroleum "eating" marine micro-organisms. Several methods were tried to stop or contain this spill but the only thing that eventually worked was the "relief" well that intersected the Ixtoc well and sealed it off with cement. Because this spill has similarities to the Louisiana spill, you can gain some perspective on these spills - and spills in general by clicking on this Wikipedia web site.
Based on three separate methodologies, the independent conclusion made by the federal-directed Flow Rate Technical Group, which has analyzed both the areal satellite coverage and the wellhead output as monitored by cameras, has determined that the overall best initial estimate for the lower and upper boundaries of flow rates of oil is not the 5000 barrels reported by BP, but is in the range of 12,000 and 19,000 barrels per day. This is, however, still not a firm number. But 19000 barrels translate into 798000 gallons per day, and for 38 days would amount to about 30000000 gallons, greatly exceeding the Exxon Valdez spill.
So, what has been done to stop the flow and seal off the well. To help in answering this, here is a quick primer on a common type of failure in an oil or gas drilling exercise.
Petroleum occurs in openings - pores and fractures - within rocks, usually sandstones. Liquid oil is generally accompanied by varying amounts of natural gas. after the reservoir is penetrated by a well, the local petroleum products move under pressure to the well pipe and are driven up to some extent by the gas and/or more customarily by a partial vacuum in the hole created by surface pumping. The emerging material can often be under such pressure that it gushes out. This needs to be controlled to avoid what is called a blowout. To accomplish this, a large apparatus, called a Blowout Preventer or BOP is commonly mounted onto the wellhead. The BOP has various "fail safe" devices designed to close the pipe stream if too much gas, or oil under high pressure, is sensed and detected. Here is a cutaway diagram with parts of a typical BOP (these can have a variety of sizes and shapes and cutoff components) and a photo of a BOP at the surface of the drilling rig:
The Deepwater Horizon accident (location referred to platform number mc252) occurred because pressurized oil, accompanied by entrained gas, reached a danger point that should have triggered the BOP action. The problem was compounded by a bad decision a few hours earlier to replace heavy drilling mud with seawater. At a critical pressure, the BOP failed to function properly because of several factors including a leak, a dead auxiliary battery, and ineffective maintenance. The gas/oil mix reached the surface, was ignited by something - perhaps a friction spark - and set off the devastating explosion that eventually doomed the platform. Oil escaped from the wellhead complex. For weeks, millions watched on TV news the camera images such as we saw above, and seen again as a reminder:
Once this scenario was set in motion, BP initiated plans to gain control over the gushing oil even as the spill grew in size and volume. This graphic depicts various options available to BP and its contractors (including Transocean and Halliburton).
New ocean-going platforms were sent in as staging units from which to conduct several efforts to stop the spill. ROVs, or Remotely Operating Vehicles, were lowered to the well both to observe the effluence and to assist in conducting steps involved in the fix. ROVs, developed both for oceanographic science studies and for drilling monitors, have TV cameras and apparatus for perform tasks. They are, in fact, classic examples of remote sensors comparable to the types considered in this Tutorial. Here is a typical ROV:
The site around the original Deepwater Horizon rig has been populated with several relief well rigs and other installations, supporting nearly 1800 workers (in 3 shifts):
The first attempt to stem the oil flow was to place a large containment shell over the BOP, collect the oil inside, and pump it to the surface. This was the arrangement:
This try failed within a day. At the high ocean bottom pressures, the physicochemistry caused the shell to be lined and clogged with methane hydrates.
The next effort, in later May, was the so-called Top Kill scheme, which has about a 60% chance of succeeding. This diagram explains the procedure.
The basic concept was to inject the well with heavy mud mixed with rubber fragments, golf balls, etc. that would counter the pressure from the gas. Millions of TV viewers watched in awe the live feed pictures supplied by BP. The writer predicted failure when this mode of imagery became commonplace:
The color of the effluent was that of the drilling mud. Thus, the pressure of the gas/oil mix was just too great for the mud injection to overcome. Top Kill was abandoned in late May.
As June opened, BP decided to attempt a maneuver that would only siphon off part of the oil. Known as DMRP (Deep Marine Riser Package), its purpose is to remove broken pipe, cut a clean condition around the main exit pipe (riser), and cap the remaining pipe with an assembly that would direct the oil into pipe reaching a surface ship. This is the setup, with BP's description beneath it:
Installing a Lower Marine Riser Package (LMRP) Cap is a containment option for collecting the flow of oil from the MC252 well. The LMRP is the top half of the blow out preventer (BOP) stack. The installation procedure first involves removing the damaged riser from the top of the BOP. A remote operated hydraulic shear made two initial cuts and then that section was removed by crane. A diamond wire saw was used to cut the pipe close to the LMRP and the final damaged piece of riser has been removed. The LMRP Cap is designed to seal on top of the riser stub. The seal will decrease the potential of inflow of seawater as well as improve the efficiency of oil recovery. Lines carrying methanol also are connected to the device to help stop hydrate formation. The device will be connected to a riser extending from the Discoverer Enterprise drillship. The cap, sometimes called the Top Cap, is shown schematically and then in place. It has succeeded to siphoning off up to 25000 barrels a day, and BP hopes to increase the amount:
While these several attempts were going on, BP, the Coast Guard, the National Guard, and private citizens (including the fishermen whose livelihoods are now totally compromised) were mobilized to clean up oil reaching the shores. Attempts to forestall this direct assault on the wetlands were along five lines: first, to break up the oil at the wellhead by injecting an emulsifier into the escaping oil; second, to spray the emulsifier (Corexit) from aircraft onto parts of the spill; third, to burn off water surface oil by controlled burns; fourth, to suck up the oil out in the Gulf, using small to large boats; fifth, to skim the oil off the surface using skimmer boats, sixth, to prevent oil from reaching the shoreline using a continuous line of booms, and seventh, once the oil has reached shore (such as the famed white sand beaches of the Gulf), remove it in a variety of ways including "brute force" shoveling by hand.
As June opened, BP and the federal government, along with many experts, shifted their attitude to one that the spilling may likely go on indefinitely. The best hope would be intersecting the original well with two relief wells (the second as backup) that should occur sometime in August. This diagram shows progress as of mid-June:
Everyday waves crashing on shore are often dominated by an oil coating, as seen in this photo:
Tar balls are common along most of the affected Gulf Coast beaches:
The oil is so pervasive it stains individual quartz sand grains:
Several of the barrier islands have been severely affected. As an example, here is the tip of one of the small Chandeleur Islands of Louisiana:
As of early July, the BP well disaster continued almost unabated, although some oil was now being captured. One of the great fears is the prediction of several severe hurricanes which could spread oil well inland. Using satellite data, daily forecasts of where the oil is and is expected soon are released.
In early July oily balls reached Galveston, TX; they may have been carried there by clinging to ships. Much more alarming is the appearance, just after the 4th of July, of tar balls in the eastern waters and shore of Lake Pontchartrain, along which New Orleans is located:
This is an unexpected development since the lake is inland. There is a narrow connection via Lake Borgne, but the pathway to that lake is itself devious relative to the Gulf's open waters.
The flow continued until mid-July:
With so much oil still escaping, BP decided to put a new, more sophisticated containment (stack) cap on the well. It was successfully mounted on July 11 and testing to determine its stability (can it withstand the pressure from the flowing oil?) is underway. The cap weighs 75 tons, as shown below. It has four outlets to which pipe will be attached; the four pipe stems will connect with 4 surface ships. It is hoped that most, if not all, the oil will be captured in the interim before the well is sealed by one (or both) relief wells.
By July 15, the 4 main valves on the cap were closed. Soon thereafter, oil ceased to gush, as shown in this ROV image of the top of the riser cap:
On July 19th, BP reported that there was some (perhaps minor) leakage in the vicinity of the wellhead. If confirmed, this would be the result of escape from rock fractures that intersect the well.
Wonder of wonders! The cap has held into August. No leakage has occurred. And, a combination of a storm and the action of dispersants has greatly reduced the amount of oil visible on surface waters. The last day in which oil could be detected by satellite was July 24th, as seen in this MODIS image:
This rapid disappearance may also be attributed to a factor that some scientists had predicted wouod occur: Marine waters contain bacteria and other organisms that feed on oil. They are abundant and "welcome" the oil as a "bonanza". This, if indeed it is happening, can account for much of the vanishing act that has removed the spill as the lead item on the network news.
To sum up efforts to contain the Deepwater spill, between April 20 and July 20 of 2010, this itemized summary was copied from CNN:1. Robots shut off blowout preventer valves. Outcome: Failed 2. Drill a relief well. Outcome: In progress 3. Install four-story containment dome. Outcome: Failed because of formation of hydrates, similar to ice crystals, that made the dome buoyant 4. "Top hat" containment device. Outcome: Abandoned before start 5. Four-inch insertion tube: Outcome: Succeeded, but had limited effect 6. Top kill (clogging well riser with drilling mud). Outcome: Failed 7. Junk shot (plugging riser with debris). Outcome: Failed 8. "Cut and cap" (cut off riser and place new containment cap). Outcome: Failed when diamond wire saw got stuck 9. Revised "cut and cap" (device placed atop jagged riser). Outcome: Some oil funneled to surface, but more still escaped 10. Second containment system (connection directly to blowout preventer funnels oil directly to ship on surface). Outcome: Oil reaches ship; operation continues 11. Better-fitting containment cap. Outcome: Oil flow shut off Thursday afternoon; test to continue for 48 hours
As of August, 2010 the estimates of the total amount of oil spilled from the Deepwater Horizon well range from 206 million gallons (4.9 million barrels) to 252 gallons (6 million barrels). If the upper limit is valid, the Gulf of Mexico spill is even more massive than the Persian Gulf spill in 1991, then the worst on record (5.7 million barrels). At its maximum outpouring, 62000 barrels a day were introduced to Gulf waters but at times this number was lower (thus the uncertainty in the range).
The good news, reached on July 15, is that the well has at last been effectively sealed. The process used is called "static kill". Heavy drilling mud has been injected through the cap and blowout preventer. It has forced the oil down the hole because it is capable of overbalancing the pressure of about 6900 psi at the well head. Afterwards, cement will be poured in to fully seal the top of the well pipe. This provides containment but as a guarantee of permanent sealing the relief wells will later seal off the bottom of the well. As September started, BP has removed the "temporary" cap used for the static kill and has put on a more effective cap.
The relief wells reached and intersected the Deepwater well in mid-September, at a depth of about 5.7 km (3.5 miles). Cement was injected into both inner and outer casings. On September 19th, 2010 the well was officially declared "dead" (permanently sealed). Gulf Coast residents breathe a huge collective "sigh of RELIEF".
But the region will need years to recover. This next chart helps to put the BP spill in perspective; it shows that over long periods cumulative leaks from natural seepage exceeds that of accidental manmade mistakes but since the seeps are widely dispersed and often far offshore, their effects usually don't threaten coastlines.
And, oil spills around the world, although infrequent, have happened repeatedly and will do so in the future as long as gasoline and motor oil continues to power automobiles. The Niger delta in Nigeria in West Africa has experienced thousands of such spills, many inland and some off coast. More than 30 million live in the Niger Delta and the Niger river floodplain. They are among many millions worldwide who have been victimized by inevitable oil spills. Check this website: Niger spills for a review of Niger's history of spills and an overview of spills in general.
So, bad as the BP spill has been - it has dominated the news and TV for parts of 5 months - Americans are not alone in their suffering. And there have been bigger spills in the past. Well over 200 million gallons were deliberately spilled by the Iraqis into the Persian Gulf during the 1991 war over Kuwait. On Jan. 23�27, 1991 in southern Kuwait, during the Persian Gulf War, Iraq deliberately released an estimated 240�460 million gallons of crude oil into the Persian Gulf from tankers 10 mi off Kuwait. Iraqi forces opened valves and emptied tankers, mostly at Kuwait's Sea Island terminal, with the intention, in part, of thwarting a landing by U.S. Marines arriving.