Not underwater as far as I'm aware, and not always "nukes", but generic powerful explosions were used to seal fountaining oil and gas wells for quite some time now. It's not the safest way around, and not the most fail-safe one, but it happened to work in most cases where it was employed.
ho-ho-hold on there cowboy. I don't know who suggested this idea, so I'm not necessarily blaming you. But your post is where I caught it.
Alllrighty, so I am definitely not an oil well expert. I could
become one in the next few years depending on an upcoming career choice, but the point is that I don't have authoritative information on this stuff. But I thought I knew about this: explosions are used to
put out fires on oil wells,
not to seal them! A quick explanation: the explosion consumes the oxygen and stops the chain reaction known as fire, causing the oil to flow sans flames. It is then much safer to approach and cap it.
And so I thought I'd look at the source material provided to see if there is some silly idea about shifting tectonics with nuclear blasts or something. From what I see in the source material, the idea is that a nuclear blast could be hot enough to cause expansion and fuse the hole shut. That's not entirely insane. However: the PDF article is extremely vague in relation to the first use and does specifically mention the need to extinguish flames. It's even less clear in the second article as to what the reasoning is behind this technique.
They have an incredibly high-pressure leak, such that capping the drilled hole simply causes it to seep through the ground itself. So they detonate a nuclear device near the cap of the gas deposit? That sounds like madness. Does anyone have a solid explanation of what exactly they are doing?