World Oilfield Forum
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.
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.