Introduction:

The Deepwater Horizon oil spill (also referred to as the BP oil spill, the BP oil disaster, the Gulf of Mexico oil spill, and the Macondo blowout) began on April 20, 2010, in the Gulf of Mexico, on the BP-operated Macondo Prospect. It is considered the largest accidental marine oil spill in the history of the petroleum industry, an estimated 8% to 31% larger in volume than the previously largest, the Ixtoc -I oil spill. The US Government estimated the total discharge at 4.9 million barrels (210 million US gal; 780,000 m3) After several failed efforts to contain the flow, the well was declared sealed on September 19, 2010. Reports in early 2012 indicated the well site was still leaking.

Fig: – Deep-water Horizon Drilling Vessel After Accident

Overview:

On April 20, 2010, at around 21:40 hrs, the uncontrollable flow of hydrocarbon fluids entered the Macondo Well. The hydrocarbons broke past all integrity barriers established to prevent any uncontrolled formation fluid flow to the surface. The rig crew was unaware of hydrocarbons in the well until the flow entered the marine riser. The well had been drilled to a Total Depth (TD) of 18,360’ which is believed to be the point of influx entry. This depth signified high-pressure formations which allowed enough force for the hydrocarbons to carry the drilling mud to surface. The rig crew encountered mud overflow onto the rig floor and attempted to divert flow into the Mud-Gas Separator (MGS) at the surface. As a result of the limited capacity of the MGS and voluminous flow from the well, the MGS eventually overflowed leading to extreme chaos on the floor. The well control equipment (The BOPs) failed to contain the flowing well fluids as both hydraulic & electric control systems had been lost. A stray source of ignition (a simple spark) ignited the hydrocarbon gases being vented from the well leading to explosions and fires that destabilized the drilling platform and killed 11 members of the crew. The destabilized platform lost dynamic positioning and this caused the marine riser to crumple, part and fall to the seafloor. The Deepwater Horizon drilling rig sank to the sea bed after burning for around 36 hours. Although the connection between the well and the rig had been severed, hydrocarbons continued to flow out of the damaged sub-sea equipment into the GOM for 87 days leading to what is now called the ‘Worst Oil Spill’ in U.S History in terms of environmental damage and human life.

Root Cause Analysis of the Disaster:

FACTOR 1: – Well Integrity Failure

  • Annular Cement Barrier
  • Shoe Track Elements

FACTOR 2: – Undetected HC entry into the well & flow until reaching the riser

  • Misinterpretation of Negative Pressure Test of Barrier Elements
  • Influx remained undetected until reaching the Marine riser
  • Well control equipment & procedures failed to maintain control of the well

FACTOR 3: – HC ignition at the surface

  • MGS vented gas onto the rig when it overflowed
  • Fire prevention systems failed to prevent HC ignition

FACTOR 4: – Emergency BOP equipment failed to seal the well

  • The final resort to seal the well failed when emergency BOP equipment on the sea bed remained non-responsive.

Impact:

The Macondo incident resulted in a Spill of 5 Million Barrels of Oil into the Gulf of Mexico. 11 Lives Were Lost with Severe Environmental Damage. Following Days of Discussions and Arguments, it was decided by BP that a Relief Well was the Most Plausible Option to Seal the Macondo Well. BP Mobilized 2 rigs (One Primary and the Other as Backup) with the Primary Rig to Drill and Intersect the Macondo Well. Cementing Operation was Carried Out and the Macondo Well was Finally Sealed after 87 Days following the Blowout.

 

Conclusions:

  • The Macondo Incident is Proof that the Industry has to adhere to the Principle: SAFETY MUST BE A HABIT AND NOT A PRACTICE.
  • The Future of Well Integrity will see Insurance Companies with Very Strict Regulations on High-Level Well Integrity Being Part of a Well Design.
  • Risk Assessment and Management will become a Critical Pre-Requisite of any Project from the Onset of its Concept Stage.
  • Whenever a Design is drafted by a Company, It has to be Reviewed/Validated by 3rd Party Consultants for Final Confirmation.

 

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