BP Deepwater Horizon Gulf Oil Spill


The CAUSE of the BP Deepwater Horizon Mexican Gulf oil spill was neither the engineers drilling below the ocean in itself nor the deep drilling in itself. 

The matter of the BP Deepwater Horizon Mexican Gulf oil spill has popped its head once more above the parapet in the prints; albeit with a much reduced prominence. It is now, you see, old news. It may have been considered to be important once: indeed it verged on the hysterical. Apparent importance as measured in the media though surely drains away merely with the passage of time if there is no new ‘shock horror’ or, worse, if the matter seems to resolve itself or even improve.

One reason for the return is that another report with important provenance [the US President’s Commission – see below for link] has supported the BP claim that the failings of BP were not the only causes of the accident. Another is because in this quarter, BP has returned to profit. But, let’s be honest, neither of these aspects are terribly sexy news topics

I have to confess that, as an engineer, I knew very little about the technology of drilling for oil.  I have to note that I am not connected to BP in any way. However, engineers can learn an enormous amount about a technology from the reports that appear in the sad wake of an accident. So it was, with the BP Deepwater Horizon Mexican Gulf oil spill. It was, undoubtedly, an extremely serious accident, killing 11 people and injuring 17  of the Rig crew, with the enormously widespread and expensive [to a vast number of innocent parties] consequences.

Everything that follows is an enormous simplification but not, as far as I can manage, greatly in error. I cannot give full details of the technology here, one, because I am far from an expert and, two, because I cannot spare at least 193 pages as in the preliminary BP report. However I will try to give a flavour of the difficulties and successes [and, in this case, failures!] of the engineers.

The technology used is quite remarkable and unlike, as far as I can see, any other engineering. In simplified terms, this is what the drilling engineers do as a matter of routine.

The engineers will drive down to a depth of three and a half miles below the surface of the ocean – not more or less – but precisely. The first part of this is to reach down to the sea bed that is itself about a mile down. Then they make a hole in the sea bed that varies in diameter from around 36 ins to around 7 ins. This hole is clad on the inside with joined up lengths of steel tube as they go deeper. Clearly, the tubes have to be somewhat smaller than the hole in order to pass down but, in order for them to be able to last for years; they have to be completely in contact with the surrounding rock. So what do the engineers do? They fill the gap at the outside diameter of the tubing with concrete. 

From the bottom of the hole upwards! 

The drilling engineers have to pump into the bottom exactly the right amount of concrete to fill the gap between the outside diameter of the tube and the hole in the rock. So they have to measure the tube clearance in the rock hole over the whole two and a half miles and calculate the volume of concrete required. And what varieties of concrete! There can be dozens of different mixes to perform properly in the different down-hole environments and to fulfil many different tasks.

When the drill hole reaches the correct depth, which is that of the oil-bearing stratum, they face another problem. A angry, heavy liquid is just bursting to surge unstoppably up the drilled hole. The crude oil is driven thus at nearly 12 000psi by a combination of artesian pressure and pressures due to dissolved gases. Similar problems face the engineers sometimes at some other strata in between

How do they stop the crude oil from thundering up the new opening to the surface that the oil has not known for some millions of years? Basically they fill the hole with a liquid that is heavier that the oil: this is what is called ‘mud’. A column of mud 3.5 miles high is enough to keep the oil down by overcoming the oil pressure.

Having arrived at this depth, the engineers have a string of tubes 3 5 miles long joined together. This string they now have to turn into a good pressure vessel that will withstand considerable pressures of around the 12 000psi. This staggering pressure can be both from the outside trying to get in but also, in other circumstances, from the inside trying to get out. Having managed to do that, by the way, the engineers have to find tests that will prove that the pressure tightness is good. No mean task in itself and highly significant it turns out.

The oil drilling engineers have always been very aware of the risks associated with the extraction of oil from the bowels of the earth. This has been in the forefront of their minds ever since the gusher became a strange symbol of oil industry success [through failure!] at least since the 1900’s. Even then they were recognised as a waste of money and a great risk to health of the drillers and damage to the equipment and the environment. From this came the first ‘blow-out preventers’.

The modern Blow Out Preventer, BOP is an enormously large complex and expensive piece of kit. Its purpose is to protect the well and the drillers and their equipment by providing several different ways of sealing the drill hole in greater or lesser emergencies. The several elaborate systems of pipe work, electrical power, electronic controls and pressure vessels make it a massive structure. It is so large and elaborate that I will not be able to say much about it here. I hope to investigate and return to discuss it further in a later posting. 

The BOP is meant to operate either on instructions from the surface drilling vessel or even, in dire emergency, automatically. That was the plan anyway.

The only effect of depth might have been that deciding on the correct mud pressures and concrete mix may have been affected by the pressures at such a great depth may have been affected by the well known exaggerated effect of the difference of two large numbers. But, compared to the other events, this is definitely a second order effect.

A Foreword to the report says many things, but it seems to be necessary to quote part of it as follows:

This is the report of an internal BP incident investigation team. The report does not represent the views of any individual or entity other than the investigation team. The investigation team has produced the report exclusively for and at the request of BP in accordance with its Terms of Reference

The Executive Summary says the following. It is rather wordy but I do not want to try to précis it and run the risk of misinterpretation.

The team did not identify any single action or inaction that caused this accident. Rather, a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces came together to allow the initiation and escalation of the accident. Multiple companies, work teams and circumstances were involved over time.

The BP Deepwater Horizon Gulf oil spill tells us so many things about the struggles of the engineers working on the needs of the world in the late Twentieth Century and the early Twenty First. None of the things that it tells us say that drilling below the ocean or drilling deep should be stopped because it is too dangerous.

Then if neither the depth nor the undersea were the cause, what was? See Part 2.

References and links

This is the BP website giving links to their initial Report in different media and at different amounts of detail.


An equally important website below is that of the US government Commission studying the accident and offshore drilling in general. This is a vital [in every sense of the word] resource that, at the time of writing is live. I was listening to part of one of the hearings streaming live with sound and slides this afternoon.


This is formally the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling. Its tasks are, firstly, to examine the facts and circumstances to determine the cause of the Deepwater Horizon Oil Disaster; secondly, to develop options for guarding against future oil spills associated with offshore drilling; and, finally, to submit a final public report to the President with its findings within 6 months of the Commission’s first meeting

You can find general oil drilling information below


This also is a good general description of the drilling process


Some websites describing drilling jargon can be found at ‘Rigzone’


Also consider Schlumberger.


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