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Uchenna Onyia's picture

The Macondo incident failed due to the failure of the BOP atop the Macondo well.  The BOP was designed to activate and seal the well if control was lost, even in a “low probability, high impact event”, such as the blowout that occurred the evening of April 20, 2010.  The report released from NAE/NRC, entitled “Macondo Well-Deepwater Horizon Blowout, lessons for improving offshore Drilling Safety”, summarized the known and suspected reasons for why the BOP failed:

There was only one Blind Shear Ram (BSR) on the Deepwater Horizon’s BOP.  A casing Shear Ram (CSR) located below the BSR was able to shear thicker pip, but was not capable of sealing the well.

The BSR was not designed to shear pipe that was under compression rather than tension.  The drill pipe on the Macondo well was under high compression, either from the weight of the pipe above, the pressure below, or both.  Also, the hydraulic pressure inside the pipe effectively created further compression.

Compression buckled the drill pipe inside the BOP, moving it off centre, so that the BSR couldn’t completely shear it and could not seal the annulus.

The BSR was designed with one V-shaped blade and one straight blade, which tests have shown requires more hydraulic pressure to shear pipe.  Also, the blades on the BSR were not wide enough to span the whole cross section of the annulus.

Attempts in the control room to initiate the ESD failed, because the multiplexing communication cables were severed in the explosion and fire.

Once communication and hydraulics were lost, the deadman system should have activated the BSR, but apparently it did not.  The BSR operated by two control pods. Investigation revealed a low batter charge in one control pod and incorrectly wired solenoid valve in the other, which may have caused the failure.


Safety Systems, “Could we have prevented the Macondo Well blowout‟, World Oil. January 2012, p. 21-22. 


Siwei Kang's picture

Whenever we talk about the Macondo accident, most of people I have known pointed that the failure of BOP is the direct cause of it. In fact, it is not the true. In general, mechanical failures, engineering design, operational implementation and poor team communication are the four major responsibilities. 

Mechanical failures such as BOP is the most obivious cause. The explosion and fire damaged the control cables of BOP Emergency mode.  Meanwhile, the Automatic Mode Function did not complete due to bad mantaince. Secondly, the potential design weakness in BOP resulted in the accident. As the blogger mentioned, only one Blind Shear Ram was designed and the Casing Shear Ram failed to seal the well. Thirdly, the bad safety management implementation made the accident become the truth. According to US offshore oil and gas regulation, regular safety check of offshore operation should be conducted every month. But the fact is the government officers had never been to the offshore platform in three years before the accident. They did the safety check in hotels everytime. Finally, poor team communication also caused this accident. In order to save money and short the schedule, the drilling manager from BP, the operator, chose unsafe operation in spite of the suggestions from contractors. Negative pressure test was accepted although well integrity had not been established. 

To sum up, many mistakes led to the accident, which gave BP disastes in financial and reputation. Until now, BP has not recovered from it.  


Reference: Final Report on the investigation of the Macondo  Well Blowout,

Uchenna Onyia's picture

uchenna onyia 51232632

Uchenna Onyia's picture

uchenna onyia 51232632

Uchenna Onyia's picture


Thanks  Siwei
Kang, for the topic. I think it is a valid one but my post actually meant
the primary cause of the Macondo incident.
There are bound to be management failures that led to the extent of
damage, loss of life and environmental pollution.
  But that does not change the fact that the
BOP was still the primary cause.
  In any
drilling operation, there are bound to be problems due to the lack concise
information about the reservoir being drilling.
Over-pressured or under-pressured formations may be encountered
unexpectedly which could potentially lead to blow outs, issues with drilling fluids
not adequately balancing the pressure experienced during drilling and other
factors which may arise.
  That is why we
need to the BOP to work as our primary source of protection.


uchenna onyia 51232632



Siwei Kang's picture

Hi, Uchenna Onyia. From my point of view, it is hard to say which one caused this accident more. BOP is only the last barrier for wells. If other mistake they made can be avoid, the accident would not become true.

faizakhatri's picture

Accident on April 2010 Macondo of well blowout explosion takes the lives of 11 workers and spills 4.9 million barrels of oil into the Gulf The main reason behind is not one to say  RCA shows it has failure of the whole system which can categories in three ways:

Physical causes –

 A process and design fault along with not fully comply with legislation failed in some way and the hydrocarbon flow form reservoir that led to blow out when drilling mud was displaced by sea water during the temporary abandonment process.which shows poor temporary procedure.Failure of the primary cementing possibly due to using “long string” well casing even after initial modelling suggested reliability problems which leads to failure of Blow Out Preventer

Human causes – 

 A lot of human mistakes,Misreading and failure of well “negative pressure tests” due to lack of standard procedures, risk assessment procedures , inadequate training for rig team and poor communication  to workers, Failure and misreading of kick detection , lack of communication with sub-contractor for drilling operations.


Organizational cause–

BP’ time saving decisions without considering the fact of  many factors such as contingency strategy for mitigation were contributing causes of the Macondo blowout, there are a lot of risk associated with deep water drilling they did not adequately identify or address risks created by late changes to well



Faiza khatri 

M.Sc oil and gas engineering

Uchenna Onyia's picture

According to
the Presidential Commission report, “The blowout was NOT the product of a series of aberrational decisions made by rogue
industry or government officials that could not have been anticipated or
expected to occur again.  Rather, the
root causes are systemic and, absent significant reforms in both industry
practices and government policies, might well reoccur.

 IN summary, there is no evidence to support an
either/or debate; the BOP did, in fact, fail to meet the safety coverage that
it was designated to provide.  Any
continuous improvement process merits the use of all available tools, including
the implications of both prescriptive and performance based standards.



SPE – 144491, “Will
Performance Based Safety Processes Prevent Future Oil Spill Disaster?”
presented at the SPE Offshore Europe Oil and Gas Conference and Exhibition held
in Aberdeen, UK, Sept. 8, 2011.

uchenna onyia 51232632
MSc Subsea Engineering

Uchenna Onyia's picture

Some Basic
recommendations were made to help prevent failure of BOPs.

BOP systems should be redesigned to provide
robust and reliable cutting and scaling, using the pipe designed for the well
and under all foreseeable operating conditions. 
The systems should be tested and verified regularly.  Operator training for emergency BOP operation
should be improved.

Instrumentation on the BOP should be improved to
enable continuous monitoring.

Instrumentation should give timely warning of
loss of well control, and the BOP’s systems should engage automatically if
conditions aren’t addressed in an appropriate amount of time.

In emergency conditions, the Emergency
disconnect system (EDS) should function independently of control from the rig,
and be linked to automatic BSR operation and sealing of the well.

All BOP systems should be testable without
compromising the integrity of the equipment.

All BOP that is not operating properly sould
cause drilling operations to cease.


Systems, “Could we have prevented the Macondo Well blowout‟, World Oil. January
2012, p. 21-22.

uchenna onyia 51232632
MSc Subsea Engineering

Catriona Ogg's picture

legislative changes which have come about as a result of the Macondo disaster,
the US Bureau of Safety and Environmental Enforcement (BSEE) published a Final
Rule in August this year.  It concludes the on-going investigation by
reinforcing the preliminary measures put in place after the incident and
listing the changes in health and safety procedures that are to be enforced.  The
main changes which pertain to BOPs can be summarised by the following measures

1) Improved casing installation
and cementing requirements and integrity tests, certified by a qualified

2) Requirement of independent
third-party verification of blind-shear ram capacity and BOP stack capacity

3) Requires secondary BOP
intervention and function testing of such (dual barrier)

4) Requires documentation to
record maintenance and inspections 

5) Requires specific well
control training with deepwater operations 

Furthermore, it provides intricate guidelines
which describe the measures in greater detail so that there is no ambiguity.

talal slim's picture

After Macondo a strong focus was given on how to improve the reliability and availability of the subsea systems .

The objective of reliability improvement is to ensure that the critical components have the expected reliability level by doing the following :

• The overall system design  is kept as simple and as robust as possible (field-proven equipment  are preferred).

• Strong emphasis on the  qualification  of the critical systems, sub-systems and equipments .
• Modifications in design  implemented in order to improve reliability (increase of MTTF), such as: change in component technology, reduction of the common failure mode etc.

The objective of availability improvement is to assess the back-up solutions and procedures that can be developed in order to be able to continue production in case of failure of a subsea item. The main areas  investigated are:

• Redundancy and diversity concept to switch to the back-up in case the primary equipment fails. Dissimilar redundancy (diversity) can further improve the reliability by reducing the probability for common cause failures.
• For items with severe failure consequences (e.g. long repair time and large production losses), contingency solutions should be assessed during design studies.
• Development of back-up/reconfiguration procedures that would allow achieving a defective function by using other item part of the System.
• Development of operating procedures in order to by-pass failed item (this can be achieved by providing flexibility in the Subsea System). 

Foivos Theofilopoulos's picture

The Macondo incident has been discussed time and time again. While most of us concentrate on the mechanical parts that failed (the integrity tests, the BOP failure), I think that Human Factors played a more important role. In the SUT lecture many of us attended about the incident (Macondo - Lessons and implications for the North Sea), one very important thing was the discussion whether there was recklessness in the actions of the people ontop the platform. Surely, the precious time lost without actions proved to be as important for the end results as the failure of the safety systems themselves. 


Foivos Theofilopoulos's picture


It is not a matter of competence. The important human factor aspects are the safety culture of the companies involved and the communication issues (as Siwei mentioned) that stalled any action from being taken until it was already too late. Searching online for reports and analysis on the incident I found an excerpt from Oil Online, from January 2011:

"As widely reported in the media, including the New York Times, BBC news, the Daily Telegraph and Aberdeen Press & Journal, an eerily similar precursor to Macondo occurred on 23 December 2009 in the UK North Sea involving Transocean and Shell. In this case, a downhole barrier was compromised and a potentially catastrophic event was averted only at the last moment when mud from the well was gushing way up the derrick; the incident being halted by one of the final ‘barriers’ on this occasion. "

What this article says is that industrial accidents are not unique. The same causes have led to similar events again and again. The fact that the industry (and the legislation) focuses more on the technical part of the failures and the new technology needed to prevent them leaves a huge gap on the part of human factors. So what can we do as safety ambassadors to help change that?



Foivos Theofilopoulos's picture

Times like these I really dislike iMechanica. I tried editing my post more than 20 times to provide the reference for the excerpt. Anyway, there goes nothing:


Dr. John Thorogood, "Macondo: the Human Factors", Oil Engineer magazine, January 2011 issue, accessed from:

Elle Allswell David's picture

The Gulf of Mexico where the Macondo accident occured is known to have high pressured Reservoirs which requires proper care while drilling through them. In a drilling operation the Mud( drilling fluid ) is the first safety barrier in stopping fluid influx into the well bore. If there is any fluid influx( Kick ) it is then necessary to weight up the drilling fluid to counter balance the formation fluid pressure. In the case of  Macondo some reports are putting the blame on poor cementing job which results in gas leakage to the top but in all the Blow Out Preventer ( BOP ) which is the Secondary Barrier and the last Resort in the case of any Blow out failed. 

To me I think the cause of the great loss is as a result of the failure of the BOP to seal the well when it was required to do so. This is as result of Mechanical Fault in the BOP which I believed was not properly tested before its installation. No matter the problem either as a result of excessive formation pressure or poor cementing job if the BOP has been able to seal the well when required the problem would have been averted.

As a result of the Macondo accident the law governing the inspection of BOPs before and during drilling operations have changed for better. It has actually brought in a lot of development to the Petroleum industry, thanks to experts that sat to review the accident and make recommendations for improvements in drilling and completion operation. 



Uchenna Onyia. I will like to disagree with you that the BOP was the primary
cause of the Macondo incident. What went wrong with the well control
before the kick came up to the well head? The BOP is supposed to be the last
line of defence. If it was the primary source does it mean there was no other
well intervention mechanism before the BOP? Can u say your kitchen was gutted
by fire because the fire extinguisher didn't work?


my opinion, the primary cause of the disaster was failure on the part of the
industry management. Using the kitchen scenario, the primary cause of the fire
was negligence to fire precautions then the bad extinguisher can come much
later as a cause.


cost or time saving decisions should come before the BOP as one of the major
cause of the blowout. The Rig crew were constantly neglecting multiple hazards
and warnings. It failed to identify and address risks created by late changes
to well design and operations on the Deepwater Horizon.


of formation fluid into the well bore is called a kick and if not controlled
can lead to a blow out. BP at various points failed to avoid the occurrence of
a kick. Long strings were used with inadequate centralizers which affected the
cementing job. Why should BP use sea water instead of mud to stabilise the well
when it was temporary abandoned? It decided not to do a complete circulation
that will remove hydrocarbon and debris from the bottom of the well before


of saying the BOP was the primary cause; the management should be blamed for
failing to take action when a leak was noticed at different times on the two
independent pods which activate the hydraulic valves of the BOP.


cause analysis should be used to assess the outcome of events. 




BP, Deepwater Horizon Accident Investigation
, Op. ct.12, p33.



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