FEATURES
 

THE 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

CHANNELLING THE OIL LEAK

The explosion and fire on the semi-submersible drilling rig “Deepwater Horizon” on Tuesday 20th April 2010, with the loss of 11 lives, and its subsequent capsize and sinking, has prompted me to write something about the manner in which jobs of this sort are usually carried out, and how the related risks are minimised. Of course we have no idea what went wrong on the rig, but almost certainly there was a leak of hydrocarbons from the well which ignited at deck level What follows is not intended to suggest what might have gone wrong on the rig. It just provides some information for those who have an interest, but who do not have detailed knowledge of the work. This is an update. See "Features" for previous:

Amidst further comment and speculation about the progress of the intervention by BP into the reservoir blowout in the Gulf of Mexico we get almost hourly updates on what is happening. The senior BP management continue to say it is not their fault, but of course those who understand something about the way these activities are undertaken, will know that the oil company, even though they may not own the equipment being used, can be responsible for the problem. A major component of the continued safety of the operation is the well plan, and no matter what other stuff is involved, the well plan must be correctly designed, taking into consideration any identified downhole problems and the reservoir structure. The BOP is the last ditch stand. So, unless something new has happened in this business, when some stuff comes bubbling up onto the drill floor several barriers will have already failed, but the driller can reach behind him and press the button to activate the BOP, or at least part of it.

 And if this activation is unsuccessful – failing to shut off the well flow – and if the rams activated were the shear rams, what on earth will any additional means of operating the BOP do? The Norwegians require acoustic means of BOP operation to be available, so that some-one in a lifeboat can dangle a transmitter over the side and operate the BOP. All one can say is that the Norwegians, earnest about safety as they are, tend to go for the ambulance at the bottom of the hill rather than the fence at the top. I hope this analogy is clear. And of course all this extra clobber on the BOP is likely to make it less reliable. Deep water BOPs are already complex bits of kit, because of the differences in pressure between the surface and the seabed. But as I have already said, they are the last barrier in the prevention of a blowout, not the first barrier.

 But to get back to the current efforts  to stem the flow, today it has been announced that an ROV (Remotely Operated Vehicle) known throughout the BP press releases so far as a “submarine”, has been successful in stemming one of the leaks. What this means of course is that a little more oil is going to come out of the other two leaks, but never mind. All will be well they hope, or at least better when the containment device is lowered over one of the remaining leaks. Apparently the Discoverer Enterprise is to be used to recover the oil and process it, and in fact store quite a bit of it. The obvious means of deployment would be for the dome to be loaded onto the drill ship, for it to be connected up to the drill string and for it then to be lowered towards the seabed. The drill ship will certainly be provided with a means of moving this object, large as it is, underneath the drill floor. The drill string could then be connected to the top and it could be lowered towards the seabed. What seems to militate against this is the fact that the cranes on the ship are not rated for 90 tonnes, apparently the weight of the structure. Like the Deepwater Horizon was, the Discover Enterprise is dynamically positioned so it does not need any moorings.

 I note that there are two apertures on the sides of the structure to be lowered, one labelled riser, and one labelled drill string and I assume that there will be a choice as to which one is used depending on how far the drill string is sticking out of the end of the riser. Either the box will be lowered over the end of the pipe, or the end of the riser, and it will sink into the mud – they hope - until the horizontal bits which are attached half way down get to the seabed. If the drill pipe is not used to lower the box, it will be lowered on a wire from a support vessel, and what-ever way it happens an ROV will be used to observe its position. When it is above the leak it will be lowered away into the correct position. An ROV would be used to disconnect the wire and assist with the connection of the drill pipe – if that is what is needed.

 Well fluids can then make their way up the drill string. They are lighter than water, and doubtless there will be a valve at the top so the flow can be stopped if necessary. It sounds as if the intention is to process the oil and then store it in the tanks on the ship. A barge has also been mentioned so one assumes that once the ship is full, the barge will be moored alongside and then filled up.

In the past I have been involved in risk assessments to assist in the recovery of offshore mobile units from emergency situations, and one hopes that this intended process has been suitably reviewed. As well as making it more likely that everyone will remain safe, often a degree of reality can be injected into a plan which may be a bit over optimistic.

 Below is a diagram of what the set-up might look like when the Discoverer Enterprise is in position.

Update on 7th May - the US Coastguard have published pictures of the containment device being lowered into the sea using a crane on the DP rig Q4000. Once it gets into position, assuming this is successful ROVs will be used to disconnect the lifting gear from the device and in some way a pipe will be connected to the top.

A picture of the Q4000 follows:

Photo Oddgeir Refvik.

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Vic Gibson May 2010

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