'Bottom Kill' Relief Wells No Sure Thing BP estimates well will close by August, but huge challenges remain By Nick McMaster, Newser Staff Posted Jun 16, 2010 3:23 PM CDT 12 comments Comments The Transocean Deepwater Discoverer drilling rig, center, and other support vessels operate over the site the Deepwater Horizon oil spill, Sunday, June 13, 2010, in Gulf of Mexico. (AP Photo/Eric Gay) (Newser) – The only technique BP has left in the fight to close the gushing oil well in the Gulf of Mexico is the "bottom kill"—in which engineers pump mud into the well using parallel relief wells. Bottom kill is difficult and dangerous, but it has a track record of stopping out-of-control wells. BP's Tony Hayward expects the relief wells—which take about 3 months to drill—to end the Gulf oil spill by early August, der Spiegel reports. But that estimate depends on engineers' abilities to intersect the spill well by digging diagonally from the relief wells. "You're trying to intersect the well bore, which is about a foot wide, with another well bore, which is about a foot wide," said the president of the American Association of Petroleum Geologists. "Hitting it with the first attempt, he adds, "would truly be like winning the lottery." Meaning Hayward's estimate could prove too rosy, again. "In the worst case, we would suddenly be dealing with two spills, and we'd have twice the problem," says a geophysicist.