Final Report on the Investigation of the Macondo Well Blowout

By Deepwater Horizon Study Group, Center for Catastrophic Risk Management (CCRM)

Deepwater memoriam victim

At approximately 9:47 p.m. (Central Standard Time) on the evening of April 20, 2010, an uncontrolled flow of water, oil mud, oil, gas, and other materials came out of the drilling riser and possibly the drill pipe on the dynamically positioned drilling vessel Deepwater Horizon owned by Transocean and contracted by BP to drill the Mississippi Canyon 252 #1 Macondo well in approximately 5,000 ft of water in the northern Gulf of Mexico offshore the coast of Louisiana.

A series of two or more explosions and a huge fire followed shortly after the uncontrolled flow commenced. The fire continued unabated for about two days fueled by hydrocarbons coming from the Macondo well. The Deepwater Horizon was abandoned shortly after the fire started, but 11 of 126 persons aboard perished. The vessel sank about 36 hours later and the fire was extinguished.

The riser and drill pipe inside bent at the top of the subsea Blowout Preventer (BOP) and dropped crumpled and broken on the seafloor, spewing gas and oil. During the next 83 days, a series of attempts were made to stop the oil from enter the Gulf of Mexico. These attempts included:

1. Closing the BOP B/S (blind / shear) rams and variable pipe rams with Remotely Operated Vehicle (ROV) intervention (failed).

2. Closing off the end of the drill pipe on the sea floor (succeeded).

3. Capturing oil spewing from the broken riser on the sea floor with a box-like containment device connected to a drilling vessel above (failed).

4. Capturing oil spewing from the riser end with an insertion tube (partially successful).

5. Capturing oil spewing from the BOP top by shearing off the bent over and ruptured riser and drill pipe inside and installing a capture device (called “Top Hat” and Lower Marine Riser Package (LMRP) Cap) (partially successful).

6. Killing the well by injecting heavy mud into the BOP. Flow at the Top Hat still persisted and partial oil capture continued afterward (failed).

7. Removing the remnant riser at the BOP top and bolting on a sealing cap with a BOP above. This succeeded in shutting the well with only a few small leaks.

8. Pumping heavy kill mud into the well to drive well effluent down and reduce pressure at the well head (succeeded).

9. Pumping cement following the kill mud to permanently seal off the flow paths. This succeeded in shutting the well with only a few small leaks.

10. During the foregoing attempts, two relief wells were drilled to provide bottom kill capability. The first relief well was able to intersect the well and permanently seal the Macondo well.

The DHSG analyses of the currently available evidence indicates the Macondo well blowout most probably was initiated with a breach in the well structure at its bottom—some 18,000 ft below the sea surface and approximately 13,000 ft below the seafloor.

The Deepwater Horizon drill crew was in the final hours of preparing the well for later production and for temporary abandonment. Undetected, a large quantity of hydrocarbons entered the bottom of the well as it was being prepared for temporary abandonment. Multiple tests failed to disclose the breach or the ingress of hydrocarbons into the well. Due to the displacement inside the well of the upper 8,300 ft of heavy drilling fluids with lighter seawater, there were large reductions in pressures inside the well that allowed substantial quantities of gases to evolve from the hydrocarbons.

As the gases rose inside the well bore, they rapidly expanded in volume as they entered the lower pressures near the surface. Seawater, drill mud, and other fluids in the well bore were pushed ahead of the rising and expanding gases. This stream of gases and fluids were followed by high-pressure oil, gases, and other fluids from the reservoir.

Last minute attempts were made on the deck of the Deepwater Horizon to divert the gases, oil, and other well fluids into an oil-gas separator. This choice was made rather than diverting the blowing out well directly overboard. The oil-gas separator was intended to prevent contamination of the seawater with the oil-based drill mud as the well fluids and gases were diverted overboard.

A similar process had been used successfully several weeks earlier to control a major ‘kick’ encountered during drilling. The volumes and pressures of the seawater, gases, drilling mud, and other fluids in the well bore overcame the separator allowing gas and the other well fluids to escape onto the drill deck and surrounding facilities.

Emergency alarms and shut-down equipment and processes failed to function. The gas ignited resulting in two or more explosions that ultimately reached the drill deck—killing the eleven workers who were struggling to stop the blowout.

The Deepwater Horizon lost all primary power generation ability. Critical pieces of emergency control equipment were destroyed and damaged and could not be or were not activated. Emergency back-up power sources could not be started. The rig was in the dark, without power, and without the dynamic positioning thrusters to maintain its location.

The rig was tethered to the seafloor with its marine riser and the drill pipe inside the riser. Multiple unsuccessful attempts were made to activate the blowout preventer located at the seafloor. The last defense against a blowout failed.

The hydrocarbons reaching the surface ignited engulfing the Deepwater Horizon in flames. The emergency disconnection system meant to allow separation of the Deepwater Horizon from the blowout preventer at the sea floor could not be activated; thus trapping the unit under and in the hydrocarbons coming from the well below.

Survivors—injured and uninjured—evacuated in nightmarish ‘Titanic like’ conditions to lifeboats which were lowered to the thankfully calm sea. Because some of the lifeboats were not fully filled and some could not be accessed, personnel left onboard evacuated by jumping overboard.

All survivors were rescued by nearby service vessels and other first responders. Heroic actions by those onboard and by the first responders saved many lives. In the following days, as the well continued to blow out, attempts were made to activate the blowout preventer using an undersea remote operated vehicle. These attempts also failed.

The Deepwater Horizon was able to sustain the effects of the blowout and the firefighting for almost two days until it sank to the seafloor some 5,000 ft below. As the drilling unit sank, the marine riser with the drill pipe inside connecting the unit to the blowout preventer and well below separated from the sinking Deepwater Horizon and collapsed to the seafloor.

Oil, gas, and other reservoir fluids were able to escape from the collapsed and fractured marine riser and drill pipe strewn across the seafloor into the waters of the Gulf of Mexico. For the next 83 days, multiple attempts were made to catch, contain, disperse, and stop the reservoir fluids from reaching the Gulf of Mexico.

All of the approved plans and preparations for controlling and mitigating the blowout repeatedly failed or were ineffective. A series of ad hoc systems were engineered, constructed, and put in place to catch and contain the oil. Another series of systems were engineered, constructed, and implemented in attempts to stop the fluids and gases escaping from the well.

The final sequence of steps to work at the Macondo BOP entailed unbolting a riser adapter at the top and bolting on a pressure-bearing cap with additional BOP components incorporated above. This allowed shutting in the well at the BOP and, eventually, kill operations to be conducted from the top. The first of two relief wells intersected the shut-in well near the productive zone shortly thereafter and mud and cement were injected there as well.

Immense amounts of toxic reservoir fluids and gases from the Macondo well were able to escape into the open waters of the Gulf of Mexico. Some of these fluids and gases reached the surface; some did not.

An unprecedented amount of dispersants introduced into the well flow stream near the seafloor prevented a large amount of the otherwise buoyant oil from reaching the surface and thereby reduced the surface impacts on nearby wetlands, wildlife, beaches, and communities. This dispersed oil and other toxic fluids from the Macondo well reservoir were transported by strong surface and subsea currents to many parts of the Gulf of Mexico.

Hydrocarbons reaching the surface were swept by the same currents into and onto adjacent wetlands and beaches. The hydrocarbon volatile components and gases were dispersed into the atmosphere. Short and long-term effects on the affected communities and marine—coastal environments are still being assessed. Similar to previous experiences associated with clean-up and containment of hydrocarbons in open water, the equipment and processes proved to be relatively ineffective.

The result of this cascade of failures is a disaster unprecedented in the history of the offshore oil and gas industry. While the impacts of these failures can be estimated in terms of the costs associated with immediate and direct injuries to human lives, property, and productivity, the costs— short and long term—to the affected publics, their industries and commerce, and the environment cannot be accurately assessed at this time.

However, it is abundantly clear that the consequences of this cascade of failures—the Macondo well project disaster—exceed by several orders of magnitude those previously experienced or thought possible.

Deepwater Horizon Macondo Well Blowout
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