Listen two these Youtube clips from Richard Hoagland in relation to the disaster in the gulf. Then raed my thoughts, explanations, and conclusions on this information below.
This bubble that he is talking about would be in the upper layers of the limestone. He said sea floor, but he was not talking about a bubble that is just sitting there at the bottom of the ocean in the water. If you ever take a look at the way that limestone is always layered, it is stratified. In other words it is never a consistent density or formation from each layer to the next.
For example, I live in Florida. I was schooled on the limestone formation layers underneath Florida when I was a golf course superintendent. There if you drilled only 1000 feet down you actually went through two sections where the limestone was a void or extremely porous.
The first open section that went under the entire souther tip of the state was the fresh water aquifer. That section was only a couple hundred feet down. The second section about 1000 feet down was the salt water aquifer that was connected to both the Atlantic ocean and also the Gulf.
So if they had drilled down 22,000 feet (about 4 miles) into the limestone, they would have gone through probably dozens of these various layers and densities of limestone. So you could imagine that this gas would be coming up from where the drill had gone into the oil field, up the drill hole, and into these less dense / porous layers of limestone.
This gas would then begin to fill that layer of limestone which could be tens of miles wide, if not hundreds. It would start to fill up that layer of limestone that is close to the surface with gas pressure.
This gas pressure would continue to build up and up and up. The layers of limestone above where the gas is building could possibly not be strong enough to contain the pressure that was building inside of this theoretical lower layer. The most probable result will be that the upper layers of lime holding the pressure in would continue to crack and release the pressure gradually.
The worst case would be that the pressure would reach a critical point and cause a huge sudden rupture in the lime. Or a gas explosion. Not an explosion of fire, more like an explosion like you had filled a gas cylinder with about 10 times to much pressure. So essentially the bottom of the ocean would explode. When this happened a huge quantity of gas would suddenly escape to the surface.
Just like in an Olympic diving pool, when you want to soften the surface tension of the water, you have bubblers that froth the surface of the pool. This would essentially happen over the surface of the Gulf. The width of the effected area would be dependent on how large of a section of the lime would let go if such an even happened.
Personally I think that this worst case stuff would only happen on a large scale like that if the limestone layers above the bubble where completely uniform in depth and strength. However, limestone does not work like that. It has weak areas and strong areas. It is more likely that the thinner weaker areas would let go in small sections which would drastically reduce the rate and violence of the relief of the gas pressure.