Page 8 - Geology and Geochemistry of Oil and Gas

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FOREWORD

The geology and geochemistry of petroleum are becoming ever more important as
the demand for fossil fuels increases worldwide. We must find new hydrocarbon
reserves that are hidden in almost inaccessible areas. Our knowledge of petroleum
geology and geochemistry is the best intellectual tool that we have for the never-
ending search for rich new deposits of hydrocarbons. The geology of the rocks under
deep oceans and on continental shelves has become much more important as
advances in technology permit drilling in these areas. Developments in petroleum
geology and geochemistry, and advances in seismic and well-logging measurements,
provide a better understanding of the evolution of subsurface sedimentary deposits
and the migration, entrapment, and production of hydrocarbons.
This book touches upon the great strides that are being made through electronic
innovations in instrumental measurements of geologic and geochemical systems. The
structure of the book is actually a balance of four topical sections. The fundamental
aspects of petroleum geology, geochemistry, and accumulation, evaluation, and
production of subsurface fluids are discussed in the first three sections followed by
the fourth section on mathematical modeling of geologic systems.
Chapters 1–3 introduce a systematic approach to understanding sedimentary
rocks and their role in the evolution and containment of subsurface fluids. This is
discussed in relation to the physical conditions of hydrocarbon reserves (e.g., at very
high temperatures and pressures).
Chapters 4–6 discuss the physical and chemical properties of subsurface waters,
crude oils and natural gases. The physical and chemical properties are especially
important to production engineering and mathematical simulation because they
impact the relative motions of fluids as saturation changes during production: (1)
wettability of rocks affects production characteristics and ultimate recovery; (2)
relative permeability affects fluid movement to the production wells; (3) density
differences between immiscible fluids affect gravity drainage from one part of the
reservoir to another as the reservoir fluids are depleted; (4) viscosity of fluids affects
the relative mobility of each fluid; and (5) fluid chemistry affects the absorption,
ultimate recovery and monetary value of the produced hydrocarbons.
Chapters 7–10 discuss the formation and accumulation of crude oils and natural
gases: (1) changes in the chemical composition of hydrocarbons that originate from
the debris of living plants to form crude oils; (2) the origins of hydrocarbons in
different areas of a single reservoir; also, the conditions which determine the
distribution of water, oil, and gas in the reservoir; (3) migration of subsurface fluids
until they eventually accumulate in isolated geologic traps; and (4) a discussion of the
oil traps as a function of sedimentary geology.