Komsomoloskaya Pravda, the best-selling Russian daily, reports that in Soviet times such leaks were plugged with controlled nuclear blasts underground. The idea is simple, KP writes: “the underground explosion moves the rock, presses on it, and, in essence, squeezes the well’s channel.”
Yes! It’s so simple, in fact, that the Soviet Union, a major oil exporter, used this method five times to deal with petrocalamities. The first happened in Uzbekistan, on September 30, 1966 with a blast 1.5 times the strength of the Hiroshima bomb and at a depth of 1.5 kilometers. KP also notes that subterranean nuclear blasts were used as much as 169 times in the Soviet Union to accomplish fairly mundane tasks like creating underground storage spaces for gas or building canals.
While the knee-jerk reaction would be to say this is madness, I've heard from a number of quarters that the ecological impact would be less than allowing the leak to continue. Still not sure about the precedent it would set though (although if a civilisation-killing asteroid was incoming I'm sure we'd all be more than happy to send a nuke up).
Interesting to note too how many nuclear blasts there have been on Planet Earth of which we remain largely oblivious.