Equipment Failure Analysis

The failure analysis of the Deepwater Horizon BOP was completed in a three-part process that began just weeks after the incident and concluded almost 14 months later.¹U.S. Chemical Safety and Hazard investigation Board. (2014, June 5). Investigation Report Volume 2: Explosion and fire at the Macondo Well. https://www.csb.gov/file.aspx?DocumentId=5931

Blowout Preventer

The BOP is subject to design capability limitations. A BOP can act as a barrier only if it is closed manually by the drilling crew or automatically as a result of a catastrophic event, such as a fire and explosion, which can trigger emergency backup systems. In manual operations, successful closure of the BOP depends on several human decisions that must be made before a well kick can develop into a blowout. Otherwise, well pressures and well flow can exceed the design capabilities of the BOP elements, leaving them unable to prevent or stop an active blowout.²U.S. Chemical Safety and Hazard investigation Board. (2014, June 5). Investigation Report Volume 2: Explosion and fire at the Macondo Well. https://www.csb.gov/file.aspx?DocumentId=5931

Automatic Mode Function (AMF)/Deadman System

No effective testing or monitoring was in place to verify the availability of the redundant systems in the emergency Automatic Mode Function (AMF)/deadman system. This emergency system was programmed to activate a blind shear ram within the BOP to shear drillpipe and seal the well.³U.S. Chemical Safety and Hazard investigation Board. (2014, June 5). Investigation Report Volume 2: Explosion and fire at the Macondo Well. https://www.csb.gov/file.aspx?DocumentId=5931

Yellow and Blue Pods Control Systems

The AMF/deadman uses two redundant control systems, the yellow pod and the blue pod, to initiate closure of the blind shear ram. This redundancy is intended to increase the AMF/deadman reliability, but on the day of the incident only one of the two pods was functioning.

Miswiring in the blue pod caused the critical 27-volt battery to drain, rendering the pod inoperable during the incident. A drained 9-volt battery in the yellow pod left one of the coils in the miswired solenoid valve inoperable, allowing the other coil to activate unopposed and initiate closure of the blind shear ram.

Factor: Miswiring in the blue pod caused the critical 27-volt battery to drain.

Finding: The blue pod was rendered inoperable on the day of the incident. It could not have closed the blind shear ram.

Factor: A critical solenoid valve in the yellow pod had also been miswired. One of the batteries was drained.

Finding: Redundant coils were designed to work in parallel to open the solenoid valve, but miswiring caused them to oppose one another. Had both coils been successfully energized, the solenoid valve would have remained closed and unable to initiate closure of the blind shear rams. However, a drained battery likely rendered one of these coils inoperable, allowing the other coil to activate alone and initiate closure of the blind shear ram.⁴U.S. Chemical Safety and Hazard investigation Board. (2014, June 5). Investigation Report Volume 2: Explosion and fire at the Macondo Well. https://www.csb.gov/file.aspx?DocumentId=5931

Buckled Drillpipe

Although the blind shear ram was activated and closed, buckled and off-center pipe in the BOP prohibited the blind shear ram from fully closing and sealing the well. The blind shear ram punctured and partially severed the pressurized drillpipe, causing flow to resume rapidly. Flow had been temporarily stopped several minutes earlier by a successful sealing with a closed BOP pipe ram.

Why did the pipe buckle? Large pressure differences were established between the inside and outside of the drillpipe when well control actions by the crew sealed the well shortly after oil and gas were released onto the rig. This likely caused drillpipe in the BOP to buckle due to a phenomenon known as “effective compression”.⁶U.S. Chemical Safety and Hazard investigation Board. (2014, June 5). Investigation Report Volume 2: Explosion and fire at the Macondo Well. https://www.csb.gov/file.aspx?DocumentId=5931

Theoretically straight pipe with equal inside and outside pressure (left); real pipe with a curve imperfection with equal internal and external pressure (center); pipe buckling as a result of increased internal pressure (right). The black wedges show the relative change in length and area of the two sides of the pipe.