Bottom Kill

Plugging Macondo, the story of how the runaway Deepwater Horizon oil well was finally brought under control

Last May I wrote about the oil drilling disaster in the Gulf of Mexico. This year I can report on the final killing of the runaway well. The story appears in the Spring issue of Mines Magazine, the magazine of the Colorado School of Mines Alumni association. The story appeared there because the two engineers in charge of the operation, Donal Fitterer and Bill McEduff, are graduates of “Mines.” You can read their story here.


The well was plugged at the top, but top plugs are often temporary solutions. What was really needed was a relief well to intersect the hole just above the oil reservoir, the so-called “bottom kill.” All they had to do was hit a basketball-sized target buried under 5,000 feet of water and 13,000 feet of rock while drilling from a randomly moving floating platform. Sounds like a high-pressure assignment, but Fitterer said, “The number one thing I learned at Mines was the ability to focus on exactly what needs to happen to get the job done. They are very big on giving you too much to do, so you have to make a decision as to what is most important.”

The technique they used was to drill the relief well, using standard directional drilling, to get close to the well at a depth. Once there, they used a ranging vector magnetometer to close in on the target which involves drilling a little, putting the instrument down the hole, then adjusting and drilling some more. The goal was to get the relief well parallel to and near the original well, then intersect the runaway well at a depth near 18,000 feet, which is just above the oil reservoir.

Positioning is achieved using a 300-foot-long assembly, which includes a 30-foot-long cylindrical beryllium copper tool equipped with a transmitter and receiver on opposite ends. Invented by Vector Magnetics, the device emits a current that sets up an electromagnetic field when conducted by the well casing. By interpreting data on the electromagnetic field picked up by the receiver, Fitterer can calculate the precise distance and direction to the blown-out well.

It only takes him two or three hours to collect these measurements, but they must be taken every 30 to 60 feet, and getting the equipment into place at the extreme depths at which they were operating was a very time-consuming process: 24 hours to withdraw the drill bit; 12 hours to lower the ranging tools, take measurements, and retrieve the equipment; and another 24 hours to lower the drill bit back into place. As a result, in the final approach, progress moved at a rate of 30 feet every 2 ½ days.

Once the original well is intersected, they could pump in heavy mud to permanently seal the well. You can watch an explanatory video of the technique here.