Page 8 - Origin and Prediction of Abnormal Formation Pressures

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PREFACE

This book's 1 goal is to provide the geologists and engineers working in the
petroleum industry with the latest knowledge on subsurface abnormally-pressured
systems associated with hydrocarbon accumulations. Abnormally high- or low-pressured
zones are succinctly defined as having a pore pressure gradient trend deviating from the
normal hydrostatic pressure gradient over a given depth range.
Drs. G.V. Chilingar, V. Serebryakov and J.O, Robertson have brought together a
team of experts who have methodically scrutinized recent scientific and engineering
developments concerning the global distribution, origins and predictions of abnormally-
pressured environments. The contributors have many years of collective experience as
geologists, geochemists, geophysicists and petroleum engineers in studying, strategiz-
ing, detecting and coping with different kinds of pressure environments and subsurface
mass transport-pressure phenomena. Their findings are based upon critical inquiry into
the scientific details behind the proposed ideas and concepts of this phenomenon. They
present an account of the nature of mass transport processes associated with such
pressure systems and their accompanying patterns of geochemical and mineralogical
changes. As petroleum engineer and geologist, I am convinced that their approach is
definitely a worthwhile effort, even if many of the relationships that have been formu-
lated and presented in the technical literature about the framework of these pressure
systems are still of an observational and empirical nature.
Exploration for large oil and gas accumulations is taking the industry into the offshore
deep-water environments on the outer continental shelf. Abnormally-high formation
pressures are ubiquitous in 'geologically' recent pelitic sedimentary environments, and
their overpressure magnitude must be by necessity identified prior to drilling and
completing a well. The subsurface pressure regime is hostile. Seismic detection and
prior knowledge on subsurface pressure conditions are prerequisites in promoting safe
drilling and development operations. Certainly, caution mitigates the risk of having
costly pressure surges and blowouts, disruption of the company's unrealized cash
stream, and occurrence of potential injury and loss of life to those individuals who are
involved in well construction. Pressure prediction is the main technology focus in the
majority of the book's chapters.
Though the topic of abnormally-pressured zones is rooted in the preceding century,
the application of thermodynamics to the physicochemical problem is just now being
explored. Recent publications are helping to recast our opinions on the origin and main-
tenance of abnormal pressure zones and the resulting physical and chemical artifacts.

1This book is contribution No. 15 of the Rudolf W. Gunnerman Energy and Environment laboratory,
University of Southern California, Los Angeles, California