AAPG Memoir 76, Chapter 1: Comparision of Overpressure Magnitude Resulting from the Main Generating Mechanisms , by Richard E. Swarbrick, Mark J. Osborne, and Gareth S. Yardley, Pages 1 - 12
from:
AAPG Memoir 76: Pressure Regimes in Sedimentary Basins and Their Prediction, Edited by Alan Huffman and Glenn Bowers
Copyright © 2001 by The American Association of Petroleum Geologists. All rights reserved.

Chapter 1
Comparision of Overpressure Magnitude Resulting from the Main Generating Mechanisms

Richard E. Swarbrick
University of Durham
Durham, England

Mark J. Osborne
University of Durham
Durham, England

BP Exploration
Sunbury on Thames, England

Gareth S. Yardley
Heriot-Watt University
Edinburgh, Scotland

ABSTRACT

Overpressure is created by two main processes: (1) stress applied to a compressible rock and (2) fluid expansion. Both processes are most effective in fine-grained lithologies, such as mudrocks and chalks. Both processes involve ineffective fluid expulsion to create pressures in excess of hydraulic equilibrium, emphasizing the importance of permeability (a poorly known rock property in fine-grained sedimentary rocks) in controlling pore pressure in the subsurface. Overpressure generation and fluid expulsion can be modeled assuming Darcy flow though a pore matrix. The basin conditions favoring high-magnitude overpressure from stress are a high sedimentation (loading) rate and/or strong lateral compressive forces. A high sedimentation rate, as a means to create rapid increase in temperature, also favors high- magnitude overpressure from fluid expansion mechanisms. An alternative method to achieve a rapid increase in temperature is a thermal pulse associated with tectonic or magmatic processes.