I will try to answer, most deep seafloor hydrate occurs in unconsolidated or semi-consolidated sediments, commonly silts, with about 50% porosity but quite low permeability, so you won’t find them below the silty bottom. The pressure of the rocks above them would crush their crystal structure freeing the menthane.
Canadian, Japanese and US research show thickness of 110 meters to 800 meters.
On land they have been found in wells drilled in the permafrost and just below the permafrost and are a hazard.
Thanks Bert!
The thought came to me today and since it was beyond my level of understanding I had to ask.
I guess if I had thought about it some more I would have eventually realized that hydrates can not exist in or below a rock layer.