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CHAPTER 7
Abnormal pore pressure
mechanisms
Contents
7.1 Normal and abnormal pore pressures 234
7.1.1 Hydrostatic pressure and normal pore pressure 234
7.1.2 Salinity effect on hydrostatic pressure 235
7.1.3 Overpressure and underpressure 236
7.1.4 Pore pressure and pore pressure gradient 238
7.2 Origins of abnormal pore pressures 241
7.2.1 Overpressures by compaction disequilibrium 241
7.2.2 Overpressures from hydrocarbon generation 243
7.2.3 Overpressures by uplift and unloading 249
7.3 Overpressures and smectiteeillite transformation 253
7.3.1 Overpressure mechanism of smectite to illite transformation 253
7.3.2 Smectite and illite transition identified by rock properties 254
7.3.3 Unloading caused by smectite and illite transformation 256
7.3.4 Smectite and illite normal compaction trend and overpressure 257
7.4 Pore pressure seals and compartments 259
7.5 Abnormal formation pressures in some petroleum basins 260
7.5.1 Global distribution 260
7.5.2 Abnormal pressure in the Macondo well of the Gulf of Mexico 261
7.5.3 Abnormal pressures in the Scotian Shelf, Canada 262
7.5.4 Abnormal pressures in the Central Graben, the North Sea 264
7.5.5 Abnormal pressures in the Cooper Basin, Australia 266
7.5.6 Abnormal pressures in China 266
7.5.7 Abnormal pressures in the Malay Basin 268
7.5.8 Abnormal formation pressures in major US shale plays 270
7.5.8.1 Pore Pressure Gradient in Major US Shale Plays 270
7.5.8.2 Bakken and Three Forks plays 273
7.5.8.3 Haynesville and Bossier shale plays 274
References 275
Abstract
Abnormal pore pressures, mostly overpressures, exist in many sedimentary formations.
The overpressures deteriorate drilling safety and may cause borehole influxes, kicks,
and even blowouts. To reduce these risks, origins and mechanisms of abnormal pore
pressures are analyzed, including compaction disequilibrium, hydrocarbon generation,
smectite diagenesis, formation uplift, and unloading. If formation overpressures were
Applied Petroleum Geomechanics
ISBN 978-0-12-814814-3 Copyright © 2019 Elsevier Inc.
https://doi.org/10.1016/B978-0-12-814814-3.00007-1 All rights reserved. 233
