On Friday Science's Richard Kerr published a story  in Science on the challenge of drilling a relief well; BP is currently drilling two  to hopefully stop the gulf gusher. Here Kerr answers questions from ScienceInsider on this high-tech method of stopping a flowing oil well.
Q: Could you quantify how difficult drilling a relief well is?
R.A.K.: Try poking a metal straw down through 5500 meters of water and nearly rock-like mud and hitting an 18-centimeter-wide target, and you'll have an idea of the challenge of drilling a relief well.
Q: What technologies make this possible?
R.A.K.: To hit the vanishingly small target, you have to know where it is and where your drill bit is, and you need to be able to steer the drill bit in the right direction. A compact inertial navigation system mounted just behind the drill bit—like those developed for missiles and submarines—tells the drill bit's position at all times to within a few meters. Remote sensing from the end of the drill pipe—acoustic or electromagnetic—lets drillers home in on the steel-cased target well. And the drill can be steered by torquing the bit in the preferred direction.
Q: How often do relief wells get drilled in the industry? Is this the standard way to close up wells?
R.A.K.: Drilling to the bottom of a blown-out well is standard operating procedure. The driller overseeing this operation for BP is 40 out of 40 for hitting target wells.
Q: What are the chances of success? What might make this effort particularly difficult?
R.A.K.: There's general agreement that this well will be killed, it's just a matter of time. But even straightforward relief well operations can take repeated tries at hitting and penetrating the well. That can be done from a single relief well, but the government required two in this case. There may be complications involving damage to the target well and surrounding rock, but there will be an end to the gushing within a few months.