ot BP oil leak

[Tim Watts]

Even better - stuff the pipe full of fully kitted islamic suicide bombers thus solving a 2nd problem simulataneously!

[Vortex5]

You're all wrong.

Looking at

reckon a few kilos Gun Gum, some opened out bean cans and giant Jubilee clips are all that's needed.

Job Jobbed.

[Adrian C]

Poppy. We've got a British expert here,

Deploy expanding foam.

That chemist chap, who must have by now have moved on from canoe work to something bigger, has some applicable references for the the job....

[Tim Streater]

Yes, thanks Ron for that exposition.

And thanks for properly snipping, unlike Messrs newshound, Dave, and Sambrook who will be getting an official tongue-lashing and

[stuart noble]

I was curious about this "heavy mud" and the "mud engineers" in charge of it. Mostly barium apparently. We don't call a barium meal a mud meal though

[Bruce]

The so-called "mud" is something rather more sophisticated than that. It is a carefully controlled slurry of processed bentonite clay in water which, with other additives, gives a heavy thixotropic goo that gels to form a semi-solid. It is widely used in the oil industry to control drilled wells, and also in the construction industry to construct concrete pile and wall foundations in difficult ground. I have had a fair amount of experience of the latter using bentonite slurry to support the ground during the construction of foundations to several prominent buildings including Lloyds of London.

So it isn't the Mickey Mouse technique that some reports suggest.

The mud is not being dumped "on top of the failed valve" (there is only one) as that would be completely pointless. It is being pumped down deep into the well tube against the flow of oil and gas coming out under pressure.

If the work goes according to plan, a column of bentonite slurry will form in the well tube, hundreds of feet high, and the weight of the heavy slurry will counter the pressure of the escaping oil and gas. The slurry will then gel, which will allow a plug of cement mortar to be formed in the well pipe above the gelled bentonite.

The operation seems to be going well, with bentonite being pumped in and the flow of oil and gas dramatically reducing. Once the flow has stopped, there is a window of opportunity to create the cement plug, and that will be that.

These are standard wellfield techniques which have been used successfully for many years (decades) on wells at ground level and in shallower water. What is novel is their use on a deep well in water that is over 5,000 feet deep.

Most of the world's untapped oil reserves are either soaked up in tar sands, as in Athabasca in Canada, or in oil fields that lie much deeper under the sea than have been exploited so far. Oil companies must now learn from BP's mistakes in the Gulf to ensure that the risk of any repeat of this disaster is reduced to the point where it has almost been eliminated.

Unfortunately, zero risk is not possible, but BP and their contractors and suppliers do seem to have made a number of basic errors which together caused the blowout and loss of life.

[Roger Morton]

it in context quite nicely

[Tim Streater]

Reading that wikipedia article, it seems that although the stuff gels, it can be forced to ungel by the application of sufficient pressure, at which point, once it starts to move, it then moves fairly easily.

It this recipe for catastrophic failure if there were a pressure pulse underground, or is that what the cement plug is for? This can't be a new point I'm raising.

Thanks,

[stuart noble]

I played with bentonite a few years back in the formulation of surface coatings. Amazing to think that 1% of a powder dispersed under sheer can produce a gel that you can stand a spoon up in. It's the "house of cards" structure that is created when the platelets are attracted end to end when the mixture is at rest. Like a lot of gels, it collapses if the ph is tweaked. IIRC atapulgite is more stable in this respect.

[geoff]

Paging Peter Parry

[Rod]

But you'd call a barium enema that and worse. Especially when splattered across floor, doors, walls and ceiling after some unfortunate patient in the X-ray department has been unable to hold on any longer...

Actually, maybe not the 'meal' bit above.

[geoff]

"... and the poor little monkey trying to put the cork back in"

as the joke goes

[Bruce]

I have had some fun with bentonite over the years. Depending on which of the two main suppliers you bought it from, it could be either a grey or a yellow powder. When you mixed the yellow powder with water, the result closely resembled custard.

I still vividly remember one day when we were excavating for a diaphragm wall foundation on a site just off Bishopsgate in the Square Mile. We had recently completed the foundations to Lloyds of London without any major problems, and picked up the new job on the basis of our track record.

I was standing next to the trench, which was by then about 14 metres deep and filled with yellow custard. We had just stopped for a 10 minute tea break. There was a gurgling sound, just like the bathwater going down the plug, and the surface of the custard rapidly dropped about five metres. We rapidly added bentonite from the on-site tank until it came back up to ground level - otherwise there was a risk the trench would collapse.

Then an immaculately dark-suited black man turned up at the gate shouting at the top of his voice. He was extremely irate. His immaculate dark suit was coated up to thigh level in yellow custard.

The man was the manager of the London branch of the national bank of a very large African state. His bank's fault was filling with custard, and he wasn't best pleased!

A structural survey later showed that his vault wall was made of unbound rubble, and the several metres of ground between his basement and the one we were constructing were also made of very weak materials.

The site investigation for our project included a borehole which went through this material but showed it to be competent London clay. I lost count of how many times this happened over the years - the drilling crew doing the borehole probably never drilled more than the first four or five metres through gravel and stopped once they got into the clay, which is much slower to drill, then wrote up the fiction in the pub. ;-)

[Bruce]

The failed blowout preventer that caused the leak was from ...

... Saniflow!

(only joking!)

[Alan]

In message , newshound wrote

And a push blanking plug

[Ron Lowe]

I don't know the pressures in that particular well, I believe it's an HPHT well ( high pressure / high temperature ) as well as being deep-water.

I can give you some sample numbers for a typical 'routine' oil well in the North Sea.

North Sea wells are typically in the range 12 - 18000 ft deep.

Let's say we have a reservior at 12,000 ft, at a reservior pressure of

7000psi.

To drill safely through this, we need to have a mudweight sufficient to over-ballance the 7000 psi by around 500psi. ( 200 - 1000 psi are typical overballances ). So we may choose a mudweight of say 12 ppg ( pounds per US gallon ). This has a gradient of about 0.624 psi/ft, and will give a hydrdostatic head of 7500psi at 12000 ft.

( Typical mudweights vary from say 9 to 20 ppg. To convert PPG to Specific Gravity divide by 8.33. From SG to gradient psi/ft multiply by 0.433, the gradient of water. )

Once the well is cased and cemented, we can circulate the mud out to something more like water. Water has a gradient of 0.433psi/ft, and so the fluid column will exert around 5200 psi at 12000 ft.

There is now a differential of around 1800psi across the casing / cement.

We then run the completion ( a 'straw' down through the centre of the casing, perhaps 5" in diameter, which we actually flow the oil through ), and perforate the well. This involves using a gun containing hundreds of shape charges of High Explosives, aimed through the casing and cement. These perforations penetrate some distance into the formation,and allow the oil into the casing and up the completion to the surface, where the drilling BOP is now replaced with a production 'christmas tree' set of valves.

The surface pressure we see is the formation pressure minus the hydrostatic head in the well-bore. Once the well is producing, the well-bore is full of oil ( gradient of let's say 0.35 psi/ft ), so the wellbore hydrostatic head is now say 4200 psi. This gives us a surface pressure of around 7000 - 4200, or say 2800psi. ( Shutin pressure. Flowing pressures are lower ).

In reality, most N Sea oil wells have surface pressures lower than this now. 1000 - 2000 psi is typical.

Typically, surface equipment is rated at 10k psi.

Gas wells will have higher surface pressures, because the hydrostatic head of the gas column is close to zero, so the surface pressure is close to reservior pressure.

Standard surface kit is available for 10k and 15k and sometimes as much as 20k. 20k and beyond is getting exotic.

HPHT is another ball game, and I'm afraid I don't have any example parameters for that.

[stuart noble]

That is fascinating. I must relate it to my mate, who spent 20 odd years testing concrete. I will also relate it to any school kids I meet who tell me that arts subjects lead to more interesting careers! Must be nice to have a job where, when someone asks you what kind of day you've had, you have something like the above to talk about over dinner.

[Dave Liquorice]

Fascinating stuff, thank you.

FWIW 5,000' of water is about 2,160 psi.

The other thing that seems to be forgotten or not mentioned is the size of the pipework. Not only are the pressures involved high the pipes are big. ISTR seeing 21" dia being mentioned some where in relation to the riser.

[geoff]

In message , Alan writes

I get the feeling that you are not taking this thred as seriously as you could

There will be a test at the end, so pay attention

[Ron Lowe]

The riser will be largeish, as you say.

The actual well ( below the BOPs ) will probably have 9-5/8" OD casing from the BOPs down to around 80-90% of it's depth. This will have an ID of just over 8.5 inches. Below that, they will have drilled ahead in a size which the drill bit could fit through the ID of the casing, usually around 8.5" hole. This is then in turn cased with a 'liner' of around 7" OD. If we want to drill ahead further, we will need to go down to a 6" hole, so the bit can fit thru the 7" liner.

Once the well is cased, we usually run a 'completion', which is a skinny 'production' pipe through the middle of all this, and this is what we actually flow the oil to surface through . The completion ( or 'tubing' ) is usually aroud 5" or less. The completion is sealed against the casing a few hundred feet above the reservoir, using a device called a 'production packer', which is like one of the bungs you get for stopping a wine bottle, with a small lever on top that extrudes rubber sealing elements out around it.

Now, the oil flows from the perforations into the casing below the packer, but can't flow up past the packer. The flow path is up through the tubing, which goes up through the packer. The annulus between the tubing and casing above the packer is de-pressurised.