Page 269 - Applied Petroleum Geomechanics

260 Applied Petroleum Geomechanics

Figure 7.20 Gamma ray and pore pressure gradients measured from the modular
formation dynamic tester (MDT, in ppg) showing two pressure compartments and a
thick seal in a well.

in two sandstones across a thick seal. Seal integrity is critical to maintain
pore pressures in a compartment or a hydrocarbon reservoir, particularly the
integrity of the top seal in the crest. If pore pressure gradient in a reservoir at
the crest is higher than the fracture gradient of the seal, then the seal would
be broken, causing the oil or gas to bleed off.

7.5 Abnormal formation pressures in some petroleum
basins
7.5.1 Global distribution

Abnormal pressures occur in a wide range of geographic and geologic
conditions. Based on the compilation of the occurrence of abnormal
pressures (Law and Spencer, 1998), there are approximately 150 geographic
locations around the world known to be abnormally pressured. Hunt
(1990) indicated that abnormal pressures were identified in about 180
basins. Nearly all the abnormally pressured regions are overpressured. All