The function of Deepwater Horizon was to complete the production well, which was very close to being done when the explosion occurred. The cause is still a mystery or hasn't been made public if it isn't. According to Oil & Gas Journal, this is what's being done to try to close off the leak: [1.]The drilling rig Development Driller III was being moved into position to drill a well to intercept the Macondo exploration well and inject a specialized heavy fluid to prevent flow of oil and gas. Workers then planned to permanently seal the original well. [2.]BP and Transocean also are using remotely operated vehicles in an attempt to activate a seabed blowout preventer on the well. In addition, [3.] they are designing and building an underwater dome to contain the oil, which then would be moved by pipe to the surface. The rig is resting on the ocean floor about 1,300 ft from the wellhead. Response officials estimate a total of 1,000 b/d of oil [now estimated at 5,000 b/d] is being released. Breaking this down further 1. Development Driller III either arrived over the site on Monday or is expected this coming Monday, wasn't sure from the article, but whichever, option one is expected to take 2-3 months at a cost of more than $400,000 per day. 2. This approach has been unsuccessful. The blowout preventer must look like it's somewhat intact, though, or they would not be pursuing this option. 3. It's unknown whether the dome approach will work, since "the technology is designed for much shallower waters than the 1,522-meter-deep well that is currently leaking." Also from WSJ, more detail about where DH was in the process when the explosion happened: Transocean officials said workers had recently finished installing a steel production pipe into the well. The pipe also had been cementing the well in place by filling up the open area between the pipe and well walls. This should have prevented oil or gas from moving up the well, said Robert MacKenzie, managing director of energy and natural resources at FBR Capital Markets and a former cementing engineer in the oil industry. "A blowout after you set your final casing and cement, I've never heard of that," he said. "I cannot recall anything even remotely close to this, in terms of magnitude and scale. This is something that is exceedingly rare."