Don, the reporters are confusing several points. I think I posted bad info on depth as a result.
The drilling ability of the Transocean rig at Macondo is roughly 30,000 feet. Its maximum drilling capability is 8000-10,000 feet of water.

Quoting from "Offshore Technology" - "The initial exploration for the project was submitted bu BP to MMS in march 2009. The plan included drilling and temporary abandonment of two exploration wells over the prospect. ........
"The rig started drilling a well at water depth of 5000ft in MC Block 252 in February 2010, but exploded during drilling in April 2010.
"The well was planned to be drilled to 18,000 feet, and was to be plugged and abandoned for later completion as a subsea producer."

Now in more detail from "O&G" - "According to the oil drum, the drilling depth at the Macondo well had reached a total depth of 18,360 feet, with the previous casing shoe at 17,168 feet. The annulus or drill hole was eight and one-half inches in diameter, with the Rotary Kelly Bushing (RKB) to mud line 5067 feet. .........
A casing was run the entire length of the drill pipe, at seven inches by nine 7/8 inches from the total depth up to the wellhead. The casing had beeb cemented using ca. 100 bbls slurry. There were no losses and the plug was bumped. No back flow was observed after displacement. Top of cement is est. at 16,200 feet.
The casing was tested to 2650 psi, with the blind shear rams closed."
The rest of the article details the sequence of events leading to the explosion, including removal of the oil-based mud.
"Some problems with the inflow-draw down test, but it was deemed satisfactory" "As a result the annular or dril pipe, would have been opened up to seawater, which meant that the oil-based mud was transferred to a supply boat...."
"........pressure from the annulus had dropped and increased, presumably due to escaping gas, which eventually led to the explosion.
The rest details the pressures, the explosion, etc.
http://www.ngoilgas.com/article/why-the-macondo-well-exploded