FEATURES
 

DEEPWATER HORIZON

Deepwater Horizon - What Have we Done to Deserve This
Deepwater Horizon - After the BP Report
Deepwater Horizon - The Investigation
The Deepwater Horizon and the Late MMS.
The Deepwater Horizon - PR and Politics
The Deepwater Horizon - Forces at Work
The Deepwater Horizon - Where Are We Now?
ROVs, Risers and Mud
The Deepwater Horizon - Later
Something about the Deepwater Horizon Accident
Channelling the Oil Leak
Preventing Fires and Explosions on Offshore Installations

ACCIDENTS
The Costa Concordia Grounding
The Loss of the Normand Rough
The Bourbon Dolphin Accident
The Loss of the Stevns Power
Another Marine Disaster
Something About the P36
The Cormorant Alpha Accident
The Loss of the Ocean Express

OPERATIONS

The Life of the Oil Mariner
Offshore Technology and the Kursk
The Sovereign Explorer and the Black Marlin
 

SAFETY
Safety Case Development
The ALARP Demonstration
PFEER, DCR and Verification
PFEER and the Dacon Scoop
Human Error and Heavy Weather Damage
Lifeboats & Offshore Installations
More about PFEER
The Offshore Safety Regime - Fit for the Next Decade
The Safety Case and its Future
Jigsaw
Collision Risk Management
Shuttle Tanker Collisions
A Good Prospect of Recovery

TECHNICAL

The History of the UT 704
The Peterhead Connection
Goodbye Kiss
Uses for New Ships
Supporting Deepwater Drilling
Jack-up Moving - An Overview
Seismic Surveying
Breaking the Ice
Tank Cleaning and the Environment
More about Mud Tank Cleaning
Datatrac
Tank Cleaning in 2004
Glossary of Terms

CREATIVE WRITING

An Unusual Investigation
Gaia and Oil Pollution
The True Price of Oil
Icebergs and Anchor-Handlers
Atlantic SOS
The Greatest Influence
How It Used to Be
Homemade Pizza
Goodbye Far Turbot
The Ship Manager
Running Aground
A Cook's Tale
Navigating the Channel
The Captain's Letter

GENERAL INTEREST

The Sealaunch Project
Ghost Ships of Hartlepool
Beam Him Up Scotty
Q790
The Bilbao OSV Conference

SOMETHING ABOUT THE DEEPWATER HORIZON ACCIDENT

There was an explosion on the semi-submersible Deepwater Horizon on 20th April 2010, which was completing a well for BP, 50 miles from the edge of the Mississippi delta in the Gulf of Mexico. Eleven of the guys on board the rig unfortunately lost their lives. Nine of them were employed by Transocean, the owners of the rig, and two of them by MI-Swaco, a service company. The rest of the crew successfully evacuated by lifeboat and were subsequently recovered to the Tidewater platform ship, Damon B Bankston, and finally landed in Port Fouchon twenty-seven hours after the incident. The rig continued to burn and gradually took on an increasing list, and slipped under the waves on 22nd April.

Today, 17th May, BP have announced that they have stemmed the leak, apparently by means of inserting a flexible tube into the end of the riser and channelling the oil flow to the drill ship Discoverer Enterprise on the surface. The Discoverer Enterprise has on  board the plant required to separate the gas from the oil, and is flaring off the gas, and is storing the oil in its tanks. Apart from anything else, this process will provide everyone with a good indication as to what the actual flow of oil from the well might be, since the storage capacity of the drill ship is known. The possible flow has been estimated as being as little as 1000 barrels per day and as much as 80,000 barrels per day. The upper figure seems to be pretty unlikely however. Today's announcement should bring some relief to the people on the gulf coast, to the US administration and also to BP. There seems to have been general amazement that the well could not just be turned off, but as everyone in the business knows, that not the way it works.

Over the last few days those of us who are still following this story have seen some witness statements appearing in the press, which, give us the opportunity of finding out just a bit more about what happened, or at least what was going on at the time. Apparently the supply ship Damon B Bankston was attached to the rig by a hose when the blowout occurred and was engaged in the task of backloading mud. Already I realise that I am lapsing into industry speak, so we'll back track a bit.
The Tidewater platform ship Damon B Bankston, photographed by Oddgeir Refvik
It seems that the well that the Deepwater Horizon had been drilling was all over bar the shouting. They would have successfully drilled into the reservoir, maintaining the integrity of the well bore and the rig, by ensuring that the oil and gas down there was kept in the proper place by the column of mud and the pressure of the pumping system. Mud or as it is more correctly known "drilling fluid" is made up of some form of oil ( they used to use diesel oil once) or water, together with chemicals, mainly baryte, which is pumped down the hole using very large pumps. The ones on the Deepwater Horizon were capable of pumping at a pressure of 7500 psi. This fluid is stored in tanks on the rig, and as well as providing a hydrostatic head brings back to the surface the debris produced by the drilling operation. While the well is being drilled the returns are analysed by mud engineers to determine what the formation is like, and whether there is any gas or oil about. Back on the rig the mud is cleaned and then pumped back down the well, and the weight of the mud plus the pressure created by the pumps keeps everybody safe.

So having been through the process of drilling the well, including casing it, which means inserting steel pipe for the whole depth, something will be done with it. If there is no oil down there, or not enough to warrant further work the well will be plugged with cement and the wellhead removed by one means or another. In the old days they always used explosives but it is possible that more scientific techniques are used today. Even if it is intended that the well will be re-entered, as was to be done in this case, it will be plugged with cement and left with just the wellhead sticking out of the seabed. So that's where they were apparently on the afternoon of 20th April. The well had been plugged with cement, and the Tidewater platform ship Damon B Bankston was attached to take the mud back to base for re-processing. There would probably have been mud in the tanks, or pits as they are known, and also mud in the well and the riser. Eventually it would all be displaced with seawater, because if the well was plugged with cement, and all the work was finished, there were be no need for the hydrostatic head.

At some point during the discharge of the mud from the rig to the ship the blowout took place, and a report by a journalist who had interviewed one of the crew said that a plume of mud and gas could be seen spurting into the air like a geyser. Apparently the ship was then instructed to let go the hose and stand off 500 metres. Within a couple of minutes there was an explosion and fire and all the lights went out.

What then of the blowout preventer, the BOP, you might ask. Well who knows. The first thing to say is that as far as the guys on the rig were concerned, even though it was still there on the seabed, they would probably not be considering it necessary for the maintenance of safety, because the cement plug was doing that. So there would be no-one's finger hovering over the buttons. And much has been said about BOP testing and BOP failures, and even about the numerous failure modes that there might be in this sort of equipment. Is the poor old drilling industry to be hoist for testing the gear? Those familiar with reliability science would tell you that the availability of equipment is determined by testing, and also that the time for which the equipment is required to be reliable is taken into account. For instance, in calculating the reliability of the equipment used for space flights, they know it only has to last for the duration of the flight. Similarly BOPs only have to last - to remain reliable - for the duration of the well, but if one is to make use of this knowledge you have to test the BOP and correct any failures before attaching it to the end of the riser and lowering it to the seabed. And as I have said before, deep water BOPs are extremely complex beasts. So who knows about the BOP. We have not heard what the actual status of the rams was after accident. Were they all still unfired, unactioned, or were they all closed about the drill pipe, with finally the shear rams almost meeting but held apart by some bits of metal in the wrong place, allowing the pressure in the reservoir to force the oil out. And what were those ROVs actually trying to do with the BOP? We little people on the outside have no idea.

So, regardless of what was happening down on the seabed, gas and oil made it to the drill floor, and of course a small volume of gas 23,000 feet down will expand quite a bit on its way up. Once more we don't know what actually happened but a sufficient volume of gas could envelope the rig seeking out any possible ignition sources. We should remember that this rig was dynamically positioned, meaning that its computers were using satellites, and probably beacons on the seabed, to identify the required position and that this information would be being transferred to the thrusters which would be turning and whirring to hold the rig over the well. The thrusters were powered by 6 Wartsila engines developing 58,000 bhp. Of course the engines can provide ignition sources and worse, they can be fuelled by gas so that even if you turn them off they don't stop. It is possible to fit engines with valves in the air intakes, which overcomes this problem, but in the case of the Deepwater Horizon would they have wanted to stop the engines since they are the means by which the rig is kept in position, or possibly changing the position. Whether those in control on the rig stopped the engines or not, survivors reported that all the power went off and that there was an explosion, possibly not in that order. So now the rig was left, being held in position by the riser, with the product from the well burning on deck. It must have been truly terrifying.

And we can speculate on why the rig sank - but on another day.

Vic Gibson 17th May 2010.

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