Subregional and local pressure compartments
Subregional or local (second- and third-order) pressure compartments can be found within normal pressure regimes or regional pressure compartments.
Subregional pressure compartments
Figure 1 is an example of a subregional compartment contained within the regional pressure compartment of the Anadarko basin of Figure 5-25.
Local pressure compartments
The fluids in a porous bioherm completely encased in shale (as shown in Figure 3) are virtually isolated from the nearby fluid systems outside the bioherm. The bioherm, then, is a pressure compartment that may or may not be abnormally pressured. Other geological features that may form local pressure compartments are fault blocks, sand lenses, and sand wedges developed in growth faults.