Zim, you'd be a tad surprised at how much water is 'buried' here on earth. Basically, anything down more than a couple of hundred feet or so of the surface, is 100% saturated. Sedimentary, fractured igneous, metamorphic.
Course that doesn't go to the 'center pf the earth - just the first few miles/decades of miles till yah hit the mantle, or it gits so hot that the water de-composes into hydrogen and oxygen.
For shales - the porosities can be less than 1% up to around 11%, depending on type, depth of burial, overpressure, and so on. Now 11% doesn't sound like much, but make that 11% of 5,000 to 30-35,000 feet of sediments, it starts to add up. Limestones and Dolomites are usually on the lower end of porosity - but CAN be quite high (think of burying the Carlsbad Caverns down a few thousand feet).
For sandstones - good clean sandstones are around 30-35% porosity, the younger they are, the better. The max porosity of a sandstone (all grains spherical and of exactly same size) is 47.6% - that comes from straight forward geometrical calculations.
http://wiki.aapg.org › Porosity
Porosity - AAPG Wiki
Sandstone pore systems. Four basic porosity types can be recognized in sandstones: (1) intergranular (primary), (2) microporosity, (3) dissolution (secondary), ... The theoretical maximum porosity for a cubic packed rock, regardless of the value assigned to grain radius, is 47.6%. Porosity values for other ...
Not sure anyone has ever attempted 'calculating' the total amount of 'buried' water that exists on earth ... but twouldn't surprise me if came out to be Atlantic sized volumes, or even more.
Just in the fwiw idlewild speculation arena fur de day.
*w*
Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good ...
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