BP will begin removing the cap on its busted oil well Saturday, part of a plan to swap out the old device with a new cap that will collect all the leaking oil within four to seven days, the company says. Removing the old cap will temporarily cause the leak to worsen, and 22 skimmers will scoop up the spewing oil before the new cap is in place. The old cap will be taken off, and then underwater robots will unscrew six bolts holding on the last bit of pipe when a robot cut off most of it last month. A sealed cap, built for this purpose with connections to the surface, will be bolted on. The move will make plugging the leak with drilling mud from the bottom easier.