How would a nuke be useful for this problem?
It would fuse everything together. And, it wouldn’t have to be that big. I think the Russians have already done this.
My first thought was that the nuke would superheat the seafloor. Turning the sand into a solid - glass. I’m not sure that it would heat it deep enough and reach into impermeable materials - probably not. Then it would just make the problem worse. Say the sand was turned into glass for a diameter of one mile. In two years you might have a bunch of oil leaking around the rim a a two-mile wide problem instead of a 36-inch (or whatever) problem.
A nuke would not be all that devasting to the area. We tried, and so did the Russians - more so, in using nukes for underwater “excavations” to create harbors.