Deepwater Horizon – Part 1

by | Oct 12, 2016

The movie, Deepwater Horizon, opened in movie theaters on September 30th.

So, we at IES decided to refresh our reader’s memory with a three-part summary of the deeply tragic event. 

Part one details the history of the Macondo Oil Well and the cause of the event.

Part two will explore the technology used to shut the well down.

And part three will look at the environmental fallout from the spill.

Deepwater Horizon History

On April 20th, 2010, the deep-water oil drilling platform, Deepwater Horizon, exploded resulting in the death of 11 of the 126 workers on the platform and a loss of well control.

Two days later the 33,000 ton Deepwater Horizon sank to the ocean floor, and oil flowed unchecked from the damaged well for over three months.

A multitude of investigations determined that the cause of the explosion and the resulting deaths was not a single technological or human failure: it was a cascade of unforeseen outcomes and unexpected system failures.

At the end of the day, there was no one person to point the finger at because it was a failure of technology and systems, and human leadership and communication. 

The National Commission on the event said it best in their Report to the President (2011)

“complex systems fail in complex ways”

The Macondo well was drilled in 5,000 feet (approximately 1 mile) of water and reached a total depth of 19,000 feet (almost 4 miles).  Due to changing schedules and unforeseen circumstances, the Macondo oil well avoided two high-risk situations but not the third.

First Situation

Drilling of the Macondo well started in 2009 by the deep-water drill platform called, The Marianas.

In November 2009, Hurricane Ida severely damaged The Marianas and forced it to abandon the Macondo well at a depth of 9,000 feet.

Due to a hasty pull-off, Marianas damaged the wellhead and left the well without installing a blowout preventer creating a potentially dangerous situation.

Second Situation

Drilling restarted when the Deepwater Horizon arrived in the Spring of 2010.

Their first task was to install the 400-ton blowout preventer, which had spent the winter on a dock in New Orleans.

Once installed, the first potential disaster created by Hurricane Ida was avoided.  However, nearing the end of the drilling operation at a total depth of 18,0000 feet, the well suffered a critical loss of drilling fluid.

Loss of fluid occurs when the pressure in the wellbore exceeds the strength of the host rock causing the drilling fluid to rush out of the borehole and into the rock formation.

As the drilling fluid floods into the rock around the borehole, well pressure decreases in the borehole, however, it is borehole pressure that prevents the underlying over-pressurized oil and gas in the reservoir at the bottom of the hole from rushing up the drill pipe and causing a blowout.

The picture below illustrates an above ground blowout, which was common before the industry learned how to manage drilling fluid density. 

oil well blowout

To prevent a Macondo well blowout, drillers immediately sealed the bottom of the well with a “well pill.”  A “well pill” is a mixture of cement and other chemicals that expand and harden very quickly. 

The “well pill” worked but the incident alarmed the drilling engineers that the host rock could not withstand the high pressure needed to keep oil and gas from blowing out the well. 

Drilling was stopped at 19,000 feet even though the plan called for a total depth of 20,000 feet.

Third Situation

Unusual conditions arose during the placement and cementing of the production casing. Production casing is a pipe that runs from the oil reservoir at the bottom of the well to the wellhead on the bottom of the ocean.

Production casing is installed by pushing a 4 to 6-inch steel pipe through the borehole – including the “well pill” – into the reservoir rock at the bottom of the well. 

There is a critical interval of time between penetrating the “well pill” exposing the borehole to reservoir pressure and the time when borehole cement around the production casing solidifies. If the production casing cement does not hold – oil and gas under reservoir pressure – can break through the cement and flow to the surface through the borehole potentially causing a catastrophic well blowout.

On April 10th, cement engineers completed placing the production cement and began post cement monitoring and testing. 

During this time, samples of the cement were undergoing integrity tests at a laboratory in New Orleans. The cement passed the 8-hour test but only marginally passed the 24- and 48-hour tests.  During the down time waiting for cement results, engineers observed fluctuating wellbore pressures. 

The engineers held several meetings to discuss the pressure fluctuations, but in the end, decided that

“all wells have their own personality and this one likes to fluctuate wellbore pressure”

Due to budget and schedule demands, the team moved on with the final positive and negative borehole pressure tests.

The well passed the positive pressure test; however, the production casing cement failed during the negative pressure test causing high-pressure oil and gas to enter the wellbore at about 19,000 feet below the surface. 

Oil and gas shot up the wellbore from the reservoir to the drilling platform expanding as pressure was released until it approached the speed of sound at the surface. 

The volatile mix of natural gas, crude oil, and brine ignited at the surface causing the fatal explosion. Ultimately the cement job had failed, and the blowout preventer failed to control the well. A picture of oil flowing from the Macondo well is shown below.


No one can point the finger at one person, process, or technology involved with the Macondo disaster or demonstrate a single act of negligence. The National Commission identified dozens of individual contributions that led to a cascade of human and technological failures.

In reality and unfortunately, what happened at Macondo was a case of prudent practitioners acting according to common practice. 

It was common practice

  • for a rig to pull off of a well because of hurricane damage to the rig
  • to install a blowout preventer that had been sitting around for months
  • in certain situations, accept fluctuating wellbore pressures
  • complete a well that barely passed the 48-hour cement test
  • and conduct a negative pressure test on a well with fluctuating pressures.

The Results & Takeaway

As a result, 11 men died; crude oil covered portions of the Gulf of Mexico; over 350 lawsuits and counter lawsuits were filed against oil companies, field service providers, drill rig operators, governments and manufacturers.

To a person, every engineer, manager and worker on the Deepwater Horizon insists they were following “normal procedures”. 

In hindsight, to a person, they all agree that they should have looked harder or conducted additional tests or followed up on so many pieces of suspect information. 

In the end, it was a collective AND individual lack of action by hundreds of people that caused the disaster.  Any one person could have broken the cascade of events that ultimately led to the catastrophic oil release.

Studies show that most accidents occur not from a single event but from a cascade of seemingly random decisions.

Our takeaway should be that safety is everyone’s responsibility and that everyone has the power to stop work, interrupt traffic, be a loud mouth – do anything, but do something – when we witness an unsafe action at work or home.

You can read the second part of this series by clicking this link: Deepwater Horizon – Part 2 – Mitigation Efforts

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