Sunday, July 18, 2010

Ixtoc 1 - No longer the biggest blowout in the Gulf

Here is the story behind one of the world's largest maritime oil spills; the Ixtoc 1 oil spill in the Gulf of Mexico.

In 1979, Petroleos Mexicanos (Pemex), the Mexican national oil company, was drilling an exploratory well they named Ixtoc 1. The well was being drilled in the Bay of Campeche in the Gulf of Mexico in 50.5 metres of water using a semi-submersible rig. On June 3rd, 1979, the rig lost control of the well and it blew out a mixture of oil and gas which very quickly caught fire.

The drilling crew lost control of the well when they hit a highly porous and permeable (a measure of the interconnectedness of the rock's pores) layer of rock at at depth of 3627 metres. When a well is being drilled, drilling mud is used to serve several functions. First, it lubricates the drilling bit as it cuts through the rock and transports the rock cuttings to the surface where they are removed from the mud as it is pumped back down the hole. The drilling mud also aids in the formation of filter cake along the outside rim of the hole; this protective coating prevents damage to porous and permeable formations by the fluids in the drilling mud. Most importantly, the hydrostatic weight of the column of mud is used to keep the fluids, be they oil, gas or water, in the subsurface. Since the formations encountered at depth have higher pressures than the atmospheric pressure that we experience at the earth's surface because of the weight of the overlying rock (and water), the fluids in the wells have a tendency to push their way to the surface, sometimes quite violently. This is what creates a blowout as we are now seeing in the Gulf of Mexico. The drilling fluids provide a delicate balance between the pressures at depth and atmospheric pressure.

In the case of the Ixtoc 1 well, when a very permeable layer of rock was encountered at a depth of 3627 metres (11,900 feet), the drilling mud flowed quickly into the formation meaning that there was very little balance to keep the oil and gas downhole. The operator decided to trip all of the drill string out of the hole so that efforts could be made to plug off the lost circulation zone, unfortunately, when they did so, they created reduced pressure that resulted in swabbing the porous zone which resulted in immediate and uncontrollable flow oil and gas. Normally, the blowout preventers (BOPs) should have activated and the shear rams should have cut through the drill pipe and sealed off the well. Unfortunately, because the drill string was being tripped out of the hole and the far heavier gauge drill collars were at the level of the shear rams, they were unable to cut through the collars and seal off the well.

When the oil and gas reached the surface it sprayed 30 metres above the platform floor and motors on the deck of the rig ignited the stream resulting in the rig catching fire and collapsing to the floor of the Gulf. Fortunately, the rig was abandoned as soon as gas and oil spray erupted from the well and there were no casualties among the 71 on board. When the rig collapsed, the end result was a tangled mass of 3000 metres of drill pipe and the remains of the rig tangled around the wellhead, which tilted the BOP off its vertical orientation. Fortunately, because the well was not as deep as the BP Macondo well, the use of remotely operated equipment was not necessary. In the case of the Ixtoc well, divers were able to access the BOP stack and attempts were made to shut in the well manually. Unfortunately, it appeared that valves in the BOP could be damaged by the pressure of the flowing fluids and it was decided that it would be better to allow the well to flow oil and gas unhindered into the waters of the Gulf of Mexico. Attempts were made to plug the well including a "junk shot" which forced pieces of metal and balls into the hole to stem the flow of hydrocarbons. Unlike BP, the Pemex junk shot attempt was partially successful; the flow was reduced to 10,000 barrels of oil per day. Pemex also attempted to place a containment dome nicknamed "Operation Sombrero" over the top of the BOP however they could not properly anchor it in place. Both of these techniques are similar to what BP used in far deeper waters at their Macondo well.

Here is a photograph of the blowout after the rig collapsed:

During the 9 months and 22 days that the Ixtoc 1 well blew out, it flowed between 10,000 and 30,000 barrels of oil per day, much of which caught fire and burned when it reached the surface. In total, it is estimated that 3.3 million barrels (139 million U.S. gallons) of crude were released in the spill, making it one of the worst in history. Nearly 500 aerial missions were flown to spread the dispersant Corexit over the spill to assist in breaking it up. Again, in this case as in the BP Macondo spill, it's interesting to note that the use of dispersants is controversial. Dispersants cause the oil to be redistributed throughout the water column; this is very hard on aquatic life such as shrimp and fish, however, it saves water fowl. As many experts have noted, this makes us feel better because we can't see dead fish but the media can expose us to heart-breaking photographs of oil-fouled birds. Unfortunately, dispersants do not work on weathered crude so by the time the crude reached the beaches of Texas in August 1979, dispersants were of no use. About 160 miles of Texas coastline were damaged by the crude. Pemex has stated that about half of the oil was burned immediately when it reached the surface of the water and that about one third evaporated.

Two relief wells were drilled and on March 23rd, 1980, they successfully sealed off the Ixtoc 1 well with cement after 290 days of "production" had reduced the flowing pressure of the oil and gas.

It is estimated that Pemex spent over $100 million to cleanup the spill but they invoked sovereign immunity (i.e. the state cannot be found guilty of a crime) when it came to paying for most compensation claims. In fact, United States businesses sued Pemex for $300 million but their request was refused under sovereign immunity.

Environmental damage was extensive, especially to the beaches of Mexico; bird, fish, squid and octopus populations were particularly heavily hit. In some areas, it was reported that catches in the fishery dropped by 50 to 70% from the previous year. Within a few years, scientists noted that fish catches had returned to normal levels and that there was very little evidence of damage. Fortunately, fewer wetlands were inundated by oil in the portions of the shoreline affected by the Ixtoc spill unlike the fragile Mississippi delta marshes that are being affected by the BP Macondo spill. Scientists that returned to the beaches of Mexico years after the spill and noted that most of the oil had weathered to tar and it no longer appeared to have a marked effect on the beach ecosystem. Fortunately, it appears that the warm temperatures in the waters of the Gulf of Mexico aided in the rapid breakdown and evaporation of the Ixtoc crude.

At this point, American residents of the Gulf can only hope that they get away with as little damage as the residents of the Mexican portion of the Gulf experienced after the Ixtoc 1 blowout. Only time will tell.

In searching the internet, I came across a blog that had some photos of the damage done by the BP blowout that I had not seen in the mainstream media. Here are some photos of the BP Macondo spill that are well worth viewing (if not more than a bit disturbing). These photos made me realize just how sanitized the coverage of this spill has been.


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  2. Thanks for the tip. It would be nice to get a bit of cash out of this blog!

  3. Great article.

    I remember when Ixtoc 1 blew. As a former geologist and frequent gulf fisherman, I wondered when the next event would occur. Unfortunately, now I know.

  4. The main sources of Drilling Fluids into water environment are accidental spillage, standing of tankers and also drill cutting processes. 3-4 million tonnes of oil gets wasted in the sea through human activities and tanker accidents.

  5. When are you going to comment on Azerbaijan blowout, Nigeria Delta and many others?