Ixtoc I oil spill

Last updated
Ixtoc I
IXTOC I oil well blowout.jpg
Location Bay of Campeche, Gulf of Mexico
Campeche, Mexico
Coordinates 19°24′30″N92°19′30″W / 19.408333°N 92.325°W / 19.408333; -92.325 Coordinates: 19°24′30″N92°19′30″W / 19.408333°N 92.325°W / 19.408333; -92.325
Date 3 June 1979 – 23 March 1980
Cause
Cause Wellhead blowout
Operator Pemex
Spill characteristics
Volume 3 million barrels (130,000,000 U.S. gallons; 480,000 cubic meters) [1]
Area 2,800 km2 (1,100 sq mi)
Shoreline impacted 261 km (162 mi)

Ixtoc I was an exploratory oil well being drilled by the semi-submersible drilling rig Sedco 135 in the Bay of Campeche of the Gulf of Mexico, about 100 km (62 mi) northwest of Ciudad del Carmen, Campeche in waters 50 m (160 ft) deep. [2] On 3 June 1979, the well suffered a blowout resulting in one of the largest oil spills in history. [3]

Semi-submersible may refer to a self-propelled vessel, such as:

Drilling rig

A drilling rig is a machine that creates holes in the earth's subsurface. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person and such are called augers. Drilling rigs can sample subsurface mineral deposits, test rock, soil and groundwater physical properties, and also can be used to install sub-surface fabrications, such as underground utilities, instrumentation, tunnels or wells. Drilling rigs can be mobile equipment mounted on trucks, tracks or trailers, or more permanent land or marine-based structures. The term "rig" therefore generally refers to the complex equipment that is used to penetrate the surface of the Earth's crust.

Bay of Campeche A bight in the southern area of the Gulf of Mexico

The Bay of Campeche, or Campeche Sound, is a bight in the southern area of the Gulf of Mexico. It is surrounded on three sides by the Mexican states of Campeche, Tabasco and Veracruz. The area of the bay is 6,000 square miles (16,000 km2) and maximum depth of the bay is approximately 180 feet (55 m). It was named by Francisco Hernández de Córdoba and Antón de Alaminos during their expedition in 1517.

Contents

Accident

Mexico's state-owned oil company Pemex (Petróleos Mexicanos) was drilling a 3 km (1.9 mi) deep oil well when the drilling rig Sedco 135 lost drilling mud circulation.

Pemex company

Petróleos Mexicanos, which translates to Mexican Petroleum, but is trademarked and better known as Pemex, is the Mexican state-owned petroleum company, created in 1938 by nationalization or expropriation of all private, foreign, and domestic oil companies at that time. Pemex had total assets worth $415.75 billion, and was the world's second-largest non-publicly listed company by total market value, and Latin America's second-largest enterprise by annual revenue as of 2009, surpassed only by Petrobras. The majority of its shares are not listed publicly and are under control of the Mexican government, with the value of its publicly listed shares totaling $202 billion in 2010, representing approximately one quarter of the company's total net worth.

Oil well boring in the Earth that is designed to bring petroleum oil hydrocarbons to the surface

An oil well is a boring in the Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released along with the oil. A well that is designed to produce only gas may be termed a gas well.

In modern rotary drilling, mud is circulated down the drill pipe and back up the well bore to the surface. The goal is to equalize the pressure through the shaft and to monitor the returning mud for gas. Without the counter-pressure provided by the circulating mud, the pressure in the formation allowed oil to fill the well column, blowing out the well. The oil caught fire, and Sedco 135 burned and collapsed into the sea. [2]

Drill pipe

Drill pipe, is hollow, thin-walled, steel or aluminium alloy piping that is used on drilling rigs. It is hollow to allow drilling fluid to be pumped down the hole through the bit and back up the annulus. It comes in a variety of sizes, strengths, and wall thicknesses, but is typically 27 to 32 feet in length. Longer lengths, up to 45 feet, exist.

At the time of the accident Sedco 135 was drilling at a depth of about 3,600 metres (11,800 ft) below the seafloor. [4] The day before Ixtoc suffered the blowout and resulting fire that caused her to sink, the drill bit hit a region of soft strata. Subsequently, the circulation of drilling mud was lost resulting in a loss of hydrostatic pressure. [5] Rather than returning to the surface, the drilling mud was escaping into fractures that had formed in the rock at the bottom of the hole. Pemex officials decided to remove the bit, run the drill pipe back into the hole and pump materials down this open-ended drill pipe in an effort to seal off the fractures that were causing the loss of circulation.

Fracture (geology) geologic structure

A fracture is any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces. A fracture will sometimes form a deep fissure or crevice in the rock. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane. Fractures can provide permeability for fluid movement, such as water or hydrocarbons. Highly fractured rocks can make good aquifers or hydrocarbon reservoirs, since they may possess both significant permeability and fracture porosity.

During the removal of the pipe on Sedco 135, the drilling mud suddenly began to flow up towards the surface; by removing the drill-string the well was swabbed (an effect observed when mud must flow down the annulus to replace displaced drill pipe volume below the bit) leading to a kick. Normally, this flow can be stopped by activating shear rams contained in the blowout preventer (BOP). These rams are designed to sever and seal off the well on the ocean floor; however in this case the drill collars had been brought in line with the BOP and the BOP rams were not able to sever the thick steel walls of the drill collars leading to a catastrophic blowout.

Blowout preventer large, specialized valve or similar mechanical device, used to seal, control and monitor oil and gas wells to prevent blowout

A blowout preventer (BOP) is a large, specialized valve or similar mechanical device, used to seal, control and monitor oil and gas wells to prevent blowouts, the uncontrolled release of crude oil and/or natural gas from a well. They are usually installed in stacks of other valves.

The drilling mud was followed by a large quantity of oil and gas at an increasing flow rate. The oil and gas fumes exploded on contact with the operating pump motors, starting a fire which led to the collapse of the Sedco 135 drilling tower. The collapse caused damage to underlying well structures. The damage to the well structures led to the release of significant quantities of oil into the Gulf. [4]

Volume and extent of spill

In the initial stages of the spill, an estimated 30,000 barrels (5,000 m3) of oil per day were flowing from the well. In July 1979, the pumping of mud into the well reduced the flow to 20,000 barrels (3,000 m3) per day, and early in August the pumping of nearly 100,000 steel, iron, and lead balls into the well reduced the flow to 10,000 barrels (2,000 m3) per day. Pemex claimed that half of the released oil burned when it reached the surface, a third of it evaporated, and the rest was contained or dispersed. [6] Mexican authorities also drilled two relief wells into the main well to lower the pressure of the blowout, however the oil continued to flow for three months following the completion of the first relief well. [7]

Pemex contracted Conair Aviation to spray the chemical dispersant Corexit 9527 on the oil. A total of 493 aerial missions were flown, treating 1,100 square miles (2,800 km2) of oil slick. Dispersants were not used in the U.S. area of the spill because of the dispersant's inability to treat weathered oil. Eventually the on-scene coordinator (OSC) requested that Mexico stop using dispersants north of 25°N. [6]

In Texas, an emphasis was placed on coastal countermeasures protecting the bays and lagoons formed by the barrier islands. Impacts of oil to the barrier island beaches were ranked as second in importance to protecting inlets to the bays and lagoons. This was done with the placement of skimmers and booms. Efforts were concentrated on the Brazos-Santiago Pass, Port Mansfield Channel, Aransas Pass, and Cedar Bayou which during the course of the spill was sealed with sand. Economically and environmentally sensitive barrier island beaches were cleaned daily. Laborers used rakes and shovels to clean beaches rather than heavier equipment which removed too much sand. Ultimately, 71,500 barrels (11,000 m3) of oil impacted 162 miles (260 km) of U.S. beaches, and over 10,000 cubic yards (8,000 m3) of oiled material were removed. [6]

Containment

In the next nine months, experts and divers including Red Adair were brought in to contain and cap the oil well. [6] An average of approximately 10,000 to 30,000 barrels (2,000 to 5,000 m3) per day were discharged into the Gulf until it was finally capped on 23 March 1980, nearly 10 months later. [8] In similarity to the Deepwater Horizon oil spill 31 years later, the list of methods attempted to remediate the leak included lowering a cap over the well, plugging the leak with mud and "junk", use of dispersants, and spending months attempting to drill relief wells. [9] [10]

Aftermath

Prevailing currents carried the oil towards the Texas coastline. The US government had two months to prepare booms to protect major inlets. Pemex spent $100 million to clean up the spill and avoided most compensation claims by asserting sovereign immunity as a state-run company. [11]

The oil slick surrounded Rancho Nuevo, in the Mexican state of Tamaulipas, which is one of the few nesting sites for Kemp's Ridley sea turtles. Thousands of baby sea turtles were airlifted to a clean portion of the Gulf of Mexico to help save the rare species.

Long-term effects

The oil that was lost during the blow-out polluted a considerable part of the offshore region in the Gulf of Mexico as well as much of the coastal zone, which consists primarily of sandy beaches and barrier islands often enclosing extensive shallow lagoons.

The oil on Mexican beaches that the authors observed in early September was calculated to be about 6000 metric tons. Based on reports from various groups and individuals, five times that figure is thought to represent a fair estimate of what had landed on Mexican beaches. Investigations along the Texas coast show that approximately 4000 metric tons of oil or less than 1 percent was deposited there. The rest of the oil, about 120,000 metric tons or 25 percent, sank to the bottom of the Gulf. [12]

The oil had a severe impact on the littoral crab and mollusk fauna of the beaches which were contaminated. The populations of crabs, e.g. the ghost crab Ocypode quadrata, were almost totally eliminated over a wide area. The crab populations on coral islands along the coast were also reduced to only a few percent of normal about nine months after the spill. [12]

One study found that the most persistent issues were pollution of estuaries and coastal lagoons lining the bay, and especially the effects on breeding and growth of several food fish species. [13]

The oil washed ashore, 30 cm (1 ft.) deep in some places, as it was pushed north by prevailing winds and currents until it crossed the Texas border two months later and eventually coated almost 170 miles (270 km) of US beaches. The beach that caused most international concern in Mexico was Rancho Nuevo, a key nesting ground for critically endangered Kemp's Ridley sea turtles which had already moved inland in their hundreds to lay eggs. By the time the eggs hatched, the oil had reached the shore.

Fishing was banned or restricted by Mexican authorities in contaminated areas north and south of the well. Fish and octopus catches dropped by 50 to 70% from the 1978 levels. [12] Some larger species with longer life spans took years to recover from the Ixtoc spill. It wasn't until the late-1980s that the population of Kemp's Ridley turtles, which lay a couple of hundred eggs a year, as opposed to the millions produced by shrimp, started recovering. The immediate losses from an oil spill continue to affect larger species for generations. [14]

There is much less information on the impact of the Ixtoc I spill on benthic species (bottom dwellers). The best studies were on the Texas coast over 1000 km from the spill. Massive kills can occur when oil reaches the benthos in sufficient quantity. The only indication of a massive kill may be the remains of the dead organisms, but if they lack hard parts there will be little evidence. [15]

A report prepared for the US Bureau of Land Management concluded with respect to the spill's effect on US waters:

In spite of a massive intrusion of petroleum hydrocarbon pollutants from the Ixtoc I event into the study region of the South Texas Outer Continental Shelf during 1979-1980, no definitive damage can be associated with this or other known spillage events (e .g ., Burmah Agate ) on either the epibenthic commercial shrimp population (based on chemical evidence) or the benthic infaunal community. Such conclusions have no bearing on intertidal or littoral communities, which were not the subject of this study. [16]

See also

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References

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  3. Elena Egawhary (7 May 2010). "How big is the Deepwater Horizon oil spill?". BBC News. Retrieved 17 June 2010. oil spilled ... first Iraq War, 1991. ... Although not a single offshore spill, it saw massive oil leaks that easily dwarf Ixtoc 1
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