Capillary entry pressure is the capillary pressure at which the nonwetting phase first displaces the wetting phase. The column height is a function of seal entry pressure and the density difference between water and hydrocarbons. Seal capacity is the capillary pressure at which hydrocarbons will leak into a seal. Breakthrough pressure is the capillary pressure at which the nonwetting phase forms a continuous network within the seal. At this pressure, the nonwetting phase will leak or flow through the seal.
Any lithology can be a seal.
All that is required is that the minimum displacement pressure of the seal rock be greater than the buoyancy pressure of the hydrocarbons in the accumulation. Thus the size of the continuous pore throats and the density of the hydrocarbons and water are of great significance. The sealing capacity along a fault is not constant. Cataclasis primarily reduces grain size by breakage, thereby packing grains more efficiently. Clay smearing includes injection of clay into a fault, deformation of shale along the fault past the reservoir lithology and deformation of shale-rich sandstones.