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How did relief wells permanently seal the damaged Deepwater Horizon well?

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Fireboats battle a blaze on the Deepwater Horizon drilling rig in the Gulf of Mexico, April 2010. — Deepwater Horizon oil spill Fireboat response crews attempt to extinguish the blaze aboard the Deepwater Horizon oil rig in the Gulf of Mexico, April 21, 2010.

To permanently seal the damaged Deepwater Horizon well, engineers utilized a procedure known as a "bottom kill." This process involved the construction of a relief well that was drilled to parallel and eventually intersect the original, damaged wellbore.1

Once the relief well successfully intercepted the original channel, cement was pumped through it to block the flow of oil and gas from the reservoir. This operation was executed on September 17, 2010, following the successful implementation of a "static kill" procedure that had used drilling mud to stabilize the well through the blowout preventer. After the bottom kill was completed and verified by a series of pressure tests, the well was officially declared completely sealed on September 19, 2010.1