BP: comment from Dutch experts on future dangers

De Volkskrant, the Netherlands ^ | July 11, 2010

[Ayn And Milton]

Hi everyone -

sorry: it's in Dutch. The core is critical comment from Dutch experts on the way BP tries to fight the oil spill. As I understand it, the company wants to 'rinse' and then pour concrete into the well. Which, according to the Dutchmen, is potentially very dangerous, because unpredictable pressure changes and differences may occur, which may results in spills for a very long time to come.

They propose something entirely else: to create 4 highly controlled drain pipes that can transport the oil to another spot nearby. This would then ensure that the above calamity can't and won't happen.

Strangest: the co. said apparently to the Dutch: thanks, but no thanks.

I really hope that there will be some sort of Congressional enquiry-in-depth that will eventually reveal each and every step in this strange, long-winded, and ominous story.

(please forgive my possible mistakes, it's the best that I could do for the mo.)

[barb-tex]

I thought that was the plan. If they can't cement this well at the surface, how will the relief wells work, 0 will have three holes to stop instead of one. barbra ann

[justa-hairyape]

So the Dutch do not like the idea of flushing mud from the Relief Well into the Wild Well ? Or are they referring to after the mud injection builds and stops the Wild Well ? I guess BP would at that time flush the lower section before injecting cement ? Sounds like that was how they lost control in the first place.

[Ayn And Milton]

It’s a difficult one. I think that they are skeptical about the idea of flushing and then filling with concrete, that’s the way the paper puts it IMHO. I’ll have a more detailed look on the competing plans later in the day. In the meantime, any info is welcome.

[justa-hairyape]

Okay. My guess would be after the Mud injection through the Relief Well stops the flow through the Wild Well. In a normal well they would then put plugs in and squeeze the cement through the plugs. The cement would force the mud away from where the cement needs to fill and then cure. They cannot use plugs here because there is no casing in the lower section where they intercept the Wild Well. So how do they move the mud from non-uniform cavities around the intercept point ? Perhaps the BP plan is to flush the intercept area with water ? That would open up areas where the cement can fill in and displace the water ? Here is a diagram of the BP plan from another freeper thread. Nothing about flushing here in the BP plan.

[Ayn And Milton]

Just what I hoped for, thanks! Will study it diligently.

[justa-hairyape]

This is the website which had the image displayed above. They describe the procedure with a little more detail.

Deepwater Oil Spil - the end game plan

[Smokin' Joe]

With the exception of Cast-Iron Bridge plugs and assorted hardware, plugs are cement, pumped into the wellbore. The reason to flush ahead of the cement is to get a good cement bond. That flush need not be a full circulating volume, just a slug pumped ahead of the cement, and the mud weight can be adjusted to keep everything (meaning formation fluid in particular) in place long enough for the plug to set.

[justa-hairyape]

With the exception of Cast-Iron Bridge plugs and assorted hardware, plugs are cement, pumped into the wellbore.

There was an illustration or video that demonstrated how they put cement in to fill the voids around a casing. They inserted physical plugs. One higher up and one down near the end of the casing. The plugs were meant to be control points for the cement. The plugs had holes in them. They inserted the cement so that the plug prevented the cement from going back up above the plugs. It flowed into the area between the two plugs and somehow ran out around the casing and filled in the annular space outside the casing. Might have been a BP video. Can try to look for that later Sunday night.

What do they flush with ? Mud or Cement or a mixture of water and either of the two ? Could there be a translation error in the Dutch article ?

[justa-hairyape]

Found it. Image from theoildrum thread. These are the plugs.

They are actually plastic plugs.

This is the thread with some very interesting additional detail.

BP's Deepwater Oil Spill - the Last Cement Job? - and Open Thread

[Smokin' Joe]

The operation you are describing is known as a "squeeze job", used to either remediate a flawed cement job or to seal off a formerly producing zone. The 'plugs' in oilfield parlance are either packers or bridge plugs, not the same as used to plug a well for permanent abandonment.

Plugging a well (p&A) is a little different, and cement plugs are 'set' by pumping in cement above formations as specified by the State of North Dakota here (where I am working now) or other governmental agency elsewhere. The cement plugs separate different potential producing horizons from one another and seal off the wellbore and are pumped in at the desired location in the wellbore. The State, here, sets minimum plug thicknesses as well (from bottom to top) and the companies I have worked for add a safety margin to ensure the requirements are met. A little more now saves a lot of problems which could occur later. When the surface plug is set, a dry hole marker is emplaced, either a plate below plow depth with the well information welded onto it or a pipe standing above the former wellhead with the same data welded onto the pipe. These are land locations, though.

The process here comes under direct state suprevision with a NDIC representative present.

The only time I have heard of an abandoned well being plugged from bottom to top was when a logging tool with a neutron source was lost in the hole and could not be fished out. That was a whole different deal, requiring red dyed cement to be pumped into the hole(total displacement) from bottom to top, among other NRC requirements.

Flushing ahead of cement can be accomplished with just about any fluid which will clean the wellbore and flush out cuttings on ledges, drilling fluid, etc.

For instance, when cementing intermediate casing, we run a salt water flush ahead of corrosion inhibitor, then follow with the cement. There is a bit more to it than that, but that is the basic order of things. The salt water flushes the invert (oil based) drilling mud off the formation, the corrosion inhibitor helps preserve the casing, and the cement holds the casing in place and seals off the annulus.

There are devices run on the outside of the casing to facillitate this, centralizers are common to keep the casing centered in the wellbore to provide a more even cement layer outside the casing, and other devices cause the cement to swirl around the pipe, helping scour the walls of the hole clean to get a good casing bond. A 'shoe' at the end protects the casing from damage or being packed with any cuttings on bottom, and a float valve (which works like a check valve preventing backwards flow) keeps the cement from flowing backwards into the casing and thus reducing the height of the cement outside the casing while the cement cures.

[justa-hairyape]

Thanks for that info. So the saltwater flushes you refer to are the ones that flush out the drilling mud after the cement bottom plugging is accomplished. They can then tap through the cement plug to begin producing. Or in the rare case where a bottom plug is used with a top plug to permanently seal off the well. Now BP originally got into trouble with the Macondo Well when they ran the saltwater flush after an improper cement job at the bottom. So the Dutch article could be referring to a similar saltwater flushing or perhaps the pre flushing before they cement the bottom plug. I wonder if BP will flush this well after the lower cement plug is in place ? This is not going to be a production well and a good cementing at the bottom may not require a cementing up top.

[Smokin' Joe]

Although the cement plugs can be permanent, they can also be drilled out by a production unit or workover rig--or even another drilling rig. If casing is set correctly through a producing zone, the cement and the casing work to keep that zone from producing until the casing is perforated.

The cement plugs are commonly a couple of hundred feet thick from top to bottom (or usually to 100+ feet above and below the top and base of the formation they are sealing off), and are set in either open hole when abandoning a well (non-producing), or casing to be drilled out later. When production casing is run and cemented in place, a cast iron bridge plug, removeable bridge plug, or a cement plug can be set in the casing to keep the well from producing until the workover rig or production unit is moved on after the drilling rig is moved off.

When the Deepwater Horizon blowout occurred, the production liner had been set, the liner cemented in at the bottom, and a plug set in the liner so the drilling rig could move off the well and a production unit could be moved in. In order to do that, the riser had to be removed, and rather than waste the oil-based drilling fluid in the riser (the pipe from the drilling rig to the BOP on the seafloor) or let that just leak into the water, the common method is to displace that fluid back to the surface (onto the rig) with seawater. This isn't flushing the wellbore, but recovering the drilling fluid while the plug keeps the well shut in.

In this case, the pressure exerted by the drilling fluid was enough to hold the formation back, but once the lower density seawater replaced that higher density drilling fluid, the pressure on the formation and the flawed plug dropped by some 2200 psi.

For whatever reason, apparently the plug leaked. Rig data charts posted on the web show that the well was flowing when the pumps on the rig were shut down, and that is a sure sign of trouble.

I can't say who or why that sign was apparently ignored--that may come out in the future--but there was a missed opportunity to avoid disaster.

The flush will help get a good cement bond in the wellbore, whether that be in the casing, through the formation, or in the space between the liner and the wall of the wellbore (the rock). That cement bond is critical to controlling the well and keeping it controlled.

I am not sure what other remediative efforts will be needed to ensure the well does not blow out again in the future, but I would think (especially in view of this mess) they will be thorough.

[justa-hairyape]

Thanks for that info. Helps to shed some light on the situation.

[Smokin' Joe]

You’re welcome!

[SunkenCiv]

Never, ever, stick your finger in a dyke.

[SunkenCiv]

Rusk. Plug the thing with rusk. There’s no other way to get rid of that.