What are they doing actually, crossing through the existing well hole?
How a relief well works:
As BP drills two relief wells in the Gulf of Mexico, we look at the process involved
BP crews are drilling two relief wells in the Gulf of Mexico (GoM) to stem the flow from the MC252 well.
BP has relief well contingency plans in place to allow the company to completely stop the flow of oil and gas from the well. These plans have now been called into action in the GoM.
A drilling rig drills a relief well or second well to intersect the original, flowing well as deeply as possible. A specialized heavy liquid is then pumped into the flowing well to bring it under control. This liquid is denser than oil and so exerts pressure (known as hydrostatic pressure) to suppress the flow of oil. Once the flow is stopped, cement is pumped into the well to completely
plug it.
Graphic depiction of BP’s progress in drilling two wells designed to intersect the original wellbore above the oil reservoir and allow heavy fluid to be pumped into the well and stop the oil from flowing
View high resolution image of the graphic (pdf, 700KB)
A relief well should be faster to drill than the original well thanks to the knowledge already gained about the geology and pressure in the reservoir. However, drilling a well of this nature presents many technical challenges to ensure that the flowing well is intersected in the right position and that the fluid and cement pumping operations are effective. BP has assembled a world-class team of experts from within the company and key specialists in the industry to ensure that the relief well operations are conducted safely and successfully.
A second relief well forms part of the contingency plans in case the first well encounters any delays. This means that progress can still be made to kill the flowing well should one drilling operation encounter a problem.
What are they doing actually, crossing through the existing well hole?
Yes that’s the goal. When they intersect the existing bore they will pump mud down to that point and let it begin to come back up the orginal bore towards the surface. They’ll keep increasing the weight of the mud until they reach a point that the length of the mud in the bore plus its weight will stop the flow. Then they can place the cement plug in.
Remember the mud was holding this well until they took it out and replaced it with sea water when they were trying to complete the final process after the first cementing job. That is when the well blew.