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BP Relief Wells-What Is A Relief Well and How Does It Work?

What Is A Relief Well and How Does It Work?


I have started this discussion  because it has become clear that many people have some misconceptions about what a relief well actually is and does. This became very apparent here when a gentleman with a PhD. wrote a letter to the President of the United States declaring that "BP was lying to us" and that his science showed that a well drilled into this blowout well would never relieve the pressure from this well.

 

I had to delete the post because it was so fundamentally wrong and misleading to readers and damaged the credibility of the Drilling Ahead site. I hope those of you with greater knowledge will help me here with your responses  to explain in simple language what a relief well is and does.

 

First-and most importantly

 

A relief well is not drilled to "relieve pressure and reduce flow of oil",

 

This seems to be the most common misconception. The sole purpose of a relief well is to kill the well completely. To accomplish this the relief well has to drill directly into the 7" casing of the blowout well at a depth of 18,000'. When this happens, a 'window" is cut into the 7" casing of the blowout well and heavy mud is forced into its wellbore. The heavy mud is calculated to counteract the force of the flow in the blowout well, In this case it should be between 14.4 ppg and 15 ppg.

 

When the flowing blowout is filled with this heavy mud the flow will stop completely and the well will become static.At this point you could completely remove the Blowout Preventers if you wanted to and you would see a pipe in the ocean floor full of drilling mud and NOTHING escaping the well.

 

 This is when the well is back in control.

 

 With this accomplished, cement from the relief well platform will be circulated into the blowout well.

 

 With the cement hardened the well will be completely and permanently sealed and abandoned.

 

The relief well is in no way meant to "just relieve pressure on the blowout well to reduce flow

 

The relief well is a permanent solution and will be successful.

 

Only 1 successful relief well is needed to completely seal  this blowout.

 

 The entire purpose of the second relief well is as a backup in the event of problems possibly encountered while drilling the original relief well. The drill string could become stuck-the drill bit could come apart-the possibilities are endless as to things that could go wrong with drilling any well, and fixing these problems could add months to the well-so a second relief well is drilled 'just in case" problems are encountered with the original relief well

 

Here is a short animation that shows a simple understanding of a relief well-what you see at the end of the video is cementing being pumped into the well

 

 

How A Relief Well Actually Works

 

 The relief well begins drilling from a safe distance form the flowing well, in this case 1/2 mile. Then the  relief well is drilled down to about 1000' above the bottom of the flowing well (the blow out) In this case somewhere around 17,000'. Special tools are then run in the hole of the relief well using wireline  that are able to sense the magnetic field of the 7" casing of the blow out well. This tells the people drilling the relief well exactly where the 7" casing is and they drill directly towards it. Several more of these wirelines are run as the new well gets closer and closer to the 7" casing to pinpoint it exactly. The relief well will be successful.

 

Here is a short video that explains how that wireline tool works.


Find more videos like this on Drilling Ahead

 

Here is a more detailed video explaining the relief well

 

 

Another misconception that we are hearing from novices is that a relief well may not be possible or effective. Nothing could be further from the truth. Relief wells have been drilled for over 30 years that I know of, possibly even longer. They were drilled then without the advanced technology we have today and were still completed successfully.

 

 Relief wells are not experimental solutions like the "Top Hat" or the "Junk Shot".

 

Relief wells are drilled every year somewhere on land or offshore to extinguish blowouts and are the accepted proven solution throughout the industry. It will be successful and it will be permanent.

Almost 30 years ago a well that was completed and producing had a blowout caused by the casing parting at over 1000' deep. This well was 30 miles from my home and involved tremendous pressures. As you can see from the photo posted below a canyon was dug all the way down to the parted casing over 1000' deep. At the same time a relief well was started from 1/4 mile away and was drilled down over 17,000' to intersect and kill the well. This was successful and accomplished then without the aid of the advanced technology we have today. It was amazing to watch and to read about in a publication then called "Drilling World". These people using very new and now primitive technology were able to find and drill into a 6" liner at these depths almost 30 years ago-then successfully kill the well with heavy mud.

 


Blowout near Allison Texas Almost 30 Years Ago

 

The Relief Well In The Distance

 

I hope this helps some of you outside the oil and gas industry understand the basics of a relief well. You can rest assured that when this relief well is completed it will be all over except for the clean up.

Tags: BP, blowout, deepwater, horizon, how, it, relief, transocean, well, works

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Replies to This Discussion

Thanks Robert,
That is a great video-I will add it to the original text above. I appreciate you sharing it
Thanks for the link, Mr. Stokesbary. The visual is instructive. "Basic" is a plus for some readers!! This operation finally makes sense now, whereas all the misinformation in the Media and elsewhere was making it impossible to grasp the reality going on way down there.

E.g., I saw one cartoon description of Deepwater Horizon having its fatal problem, and depicting caissons breaking in half and falling like tinker toys under the rig. Whoever drew that apparently thought that DWH was founded on solid ground?! The fiction being propagated is phenomenal. Imagine caissons a mile tall and reaching to the ocean floor!! Made of what, tubular steel? And that would be what, an inch thick walls? And that would weigh what, (4- 20-foot dia. columns, or, 251 sq. ft./ft of height x 100#/sq. ft. x 5280 ft./mi. x 5 miles) 331,300 TONS OF STEEL? ("tonnes" in British!) The logistics of construction boggle the mind. They would have to splay out at least one degree, and would therefore be trying to fall over at all times, in the OCEAN, remember. Who's going to set those, and keep them from falling over in the process? What happens when salt water corrodes them and they start to sag? Do they need intermittent bracing -- made of what? Oh, and then the well FAILS and the columns have to be MOVED to a NEW LOCATION??
Just to muddy the waters further...

The active mud system at the time of the incident had a density of 14 ppg. The trip slug pumped to pull pipe (the last mud pumped) was 16 ppg. This is information from the daily drilling report posted on congressional investigation exhibits site.

There was a schematic released by BP some time ago (possibly posted as another exhibit? - sorry don't recall where I got it) that outlined the casing and liner seats, estimated cement tops, drilling assembly types and much more. Included in the assorted notes is a pore pressure for the payzone equivalent of 12.6 ppg and a BHT of 262 F.

Also of note are the reports of loss zones between the 9 7/8" drilling liner shoe at 17168' and the top of the pay at 18083'. Supposedly the loss zones were a primary factor in the decision to use faomed cement. What I have not been able to determine is whether or not the loss zones are expected to be covered by the cement top. A moot point at best, because I firmly believe the cement job is pooched.

BP plans to set the last liner in the relief well just above the depth of the 9 7/8" drilling liner shoe in the original wellbore. I would speculate that they choose to do so to be prepared for losses to the annulus of the original wellbore through those loss zones.

Many moons ago in the early days of relief well drilling, it was not absolutely necessary to intersect the wellbore itself. For a well to be capable of blowing out it must have permeability - ie the ability to pass fluid through it. If so it would probably pass kill fluid too, especially with enough horsepower. Is the Halliburton pump vessel (the Q4?) the one equipped for offshore frac stimulations?

There is talk of "fracing into the original well" in assorted stories detailing early wild well operations involving relief wells. There is also much discussion of pumping tracer chemicals down the relief wells and watching the color of the flames on the burning blown out well. A color change meant communication....
Hi, Cam:
An Oil and Gas Journal article dated June 21, 2010 by Guntis Moritis has the BOP stack and casing program in diagram form. That may be the article you mentioned.
BK
The document I referred to with all the well info on it was a pdf I downloaded from somewhere probably here, but I don't have the link anymore :(

As a memory jog, it illustrates only from the seafloor down, but is quite comprehensive with detail no-one but BP, Transocean, or Halliburton would have like shoe depths and liner tops accurate to the foot, cement tops, BHA types, casing weights&grades, mud types and densities, FLOT info, etc. It even has the casing rupture disk depths and ratings, approximate mud/seawater depths in the hole, and the existing BHA with the drillpipe and tubing snorkel string.

Presumably the pore pressure measurement would have come from a wireline RFT (repeat formation tester) type tool.

Editted P.S. Found it! It was on this site under a different heading. Here's a link.. http://app4.websitetonight.com/projects/3/2/6/1/326131/uploads/Maco...
That is a good, readable diagram. I am wondering if the top of cement is a measured top or an estimate. If it is a true top then there is about 132 feet of formation exposed to the annulus of the 7" casing. But who knows what is really correct!
BK
Thanks all for this discussion--it badly needed to be started to dispell the erroneous assumptions widely held by the general public that follow these discussions. I'm not very up to speed on it myself, and these articles and vids are really appreciated.

Regarding the exposed formation:

How will this affect BP's mud weight and pump rate once the windows are cut in the casing? (I've read posts in different places that it will be a delicate balancing act to avoid casing rupture if weight/pressures are too high for the casing)

Am I correct in understanding that multiple windows will be cut simultaneously?

Does the siesmic imaging technology exist to determine beforehand if there are/is, a large "cavern" hollowed out by the outflow in this particular well?

Thanks guys.
There very well could be an enlarged "cavern" around the 7" casing in the "open hole" area between the 9-7/8" liner shoe at 17,168' and the TOC around the 7" long string (but do we know where the TOC really is?). The float collar was set at 18,115. I doubt that the shoe joint (s) was drilled out and there is no indication that the "pay zone" was perforated. Therefore it makes no sense to drill into the well below 18,114'. The most likely area to drill in to the well should be between the top of the float collar and the bottom of the 9-7/8" liner at 17,168'. It will be interesting to see where they go into the wellbore.
An interesting story in the Dalls Morning News this morning said a Wall Street Journal story Thursday indicated the British Prime Minister David Cameron is scheduled to viist the White House on July 20th and BP might shoot for that date or sooner to kill the well. Such is politics!
BK
Hi Don- from what I am hearing the relief well will be drilled to TD-(then I am assuming some of this...)they will start with setting a open hole whipstock at the lower depth and mill a window there...then move up the well as needed with whipstocks and do the same. I have also heard of them using a perf gun instead of the whipstocks to get into the original well....both of the plans above come from a good source-will be interesting to see how it plays out.

The reason for going to TD before attempting to cut a window is if they miss on the first attempt they can just pull up hole and try again-whereas if they just drilled to the original hole and took a stab at it and missed, they would have to pull back ,cement and redrill that section for another stab.

Drilling down along side the well will provide them with many shots at it quickly.
JMO
IF the flow path is up the exterior of the last casing string (as I would expect in light of what I've read here and elsewhere), does it make any sense to even make an effort to get into the last casing? It would seem likely to me that there will be communication to surface up the annulus that will hamper efforts to get communication up the inside of the original cased wellbore.
I think that is the reason for multiple windows- to get at both strings...just thinking out loud here
It appears that the latest capping stack BOP is on the Transocean Discover and is ready to go into place. Anyone know when this might occur??
BK

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