THE LINK BETWEEN ANOMALOUS PRESSURES AND GEOLOGIC FORCING
Γd = Γl/K
where l the distance from a domain's center to the nearest boundary and K is the domain hydraulic conductivity. Γd characterizes the ability of geologic forcing to generate and maintain anomalous pressures. Specifically, significant pressure anomalies will exist when Γd ≥ ~1. Thus, where anomalies are present, the value of Γ, l, or K can be estimated if the other two quantities in Γd are known. Recent findings, however, complicate this picture by suggesting another mode of pressure generation, osmosis, is significant in the subsurface. New in situ and lab experiments imply that shales and claystones can generate excess pressures up to ~ 30 MegaPascals where large differences in solute concentration exist. Osmotic pressuring does not result from dynamic geologic forcing; instead the pressure energy is derived from preexisting differences in chemical potential.