One would think that water's density is smaller than the rock. Why wouldn't it eventually rise to the surface above the denser material if the surrounding rock wasn't solid?
1) Porosity is the ratio of the volume of openings (voids) to the total volume of material. Porosity represents the storage capacity of the geologic material. On the other hand, permeability is a measure of the ease with which fluids will flow though a porous rock. Although a rock may be highly porous, if the voids are not interconnected, then fluids within the closed, isolated pores cannot move. This situation is commonly found in nature and represents a challenge for the extraction or the injection in reservoirs.
Nevertheless, I have no idea of the porosity level that could exists at those depths.
2) At 700km depth pressures are of order 21 Giga Pascals (~207000 atmospheres) and temperatures about ~1900ºC. Water is not the water we know at these conditions, it is a supercritical fluid. The line separating liquid and gas phases ended at much lower temperatures.
I thought at those depths the rock isn't solid, so why would water (or supercritical fluid) need a lot of pores to go through? Not to mention, can't supercritical fluids effuse through solids?
