Figure 2. Definitions of the porosity parameters introduced in the model. The hydrostatic porosity distribution, pH, is the porosity distribution resulting from equilibrium compaction (i.e., no pore fluid overpressures are generated). The function pH = f (z) is called the "(hydrostatic) normal trend of compaction." The measured porosity, p, is equal to pH only in the hydrostatically pressured formations. The case p > pH corresponds to undercompacted formations. The case p d pH corresponds to overcompacted formation. If fluid overpressures result from a compaction disequilibrium process, the difference p - pH = is called the "excess porosity" and can be directly related to the fluid overpressure dp.

Figure 2. Definitions of the porosity parameters introduced in the model. The hydrostatic porosity distribution,

_H, is the porosity distribution resulting from equilibrium compaction (i.e., no pore fluid overpressures are generated). The function

_H = f (z) is called the "(hydrostatic) normal trend of compaction." The measured porosity,

, is equal to

_H only in the hydrostatically pressured formations. The case

_H corresponds to undercompacted formations. The case

_H corresponds to overcompacted formation. If fluid overpressures result from a compaction disequilibrium process, the difference

_H =

is called the "excess porosity" and can be directly related to the fluid overpressure