Page 15 - Geology of Carbonate Reservoirs

xii PREFACE

the scope, purpose, and size limits of this book. I have tried to address these potential
shortcomings by including suggestions for additional reading at the end of each
chapter. This is a book for students — not for experts. Having taught university
classes and continuing education courses for the past 38 years, I have learned that
there are limits to what can be taught effectively in one university term or in a
continuing education short course. I limited the material in the book to that which
I believe can be taught in one university term or an intense, week - long short course.
Clearly, I had to choose subjects and reference material carefully, focusing on the
subjects I have found most helpful in understanding carbonate rocks and reservoirs.

Other texts on carbonate reservoirs, including those by Chilingar et al. (1992) , Lucia
(1999) , and Moore (2001) , concentrate on engineering aspects of carbonate reser-

voirs (Chilingar and Lucia) or on sequence stratigraphy as it relates to carbonates
(Moore), but they are not textbooks on the general geology of carbonate reservoirs.
I have written this book to help university students and industry professionals learn
more about how, when, why, and where carbonate reservoirs form, and about how
to recognize, analyze, and map the end - member reservoir types in carbonates —
reservoirs with depositional, diagenetic, or fracture porosity systems. Special empha-
sis is given to relationships between genetic pore types and carbonate reservoir

properties. To that end, a new classification of carbonate porosity that focuses on
the genetic pore types is presented. Two themes are repeated throughout the book:
(1) it is not possible to understand carbonate reservoirs without looking at the rocks;
and (2) one cannot accurately predict the spatial distribution of rock and reservoir
properties that are linked by cause – effect mechanisms without using a genetic clas-

sification of carbonate porosity.
Development geologists and engineers will fi nd the book useful, as will explora-
tion geophysicists and geologists. Development geologists and engineers will fi nd
the book helpful because it emphasizes the relationships between rock and reservoir
characteristics. Explorationists should find the distinction between genetic pore

types in carbonate reservoirs helpful because exploration strategies need to be built
around geological concepts that are in turn based on knowledge of how and where
porosity and permeability may occur together in depositional and diagenetic facies
or in fractured rocks.
There is a tradition among petroleum geologists to search for analogs or “ look -
alikes ” for exploration or production prospects. This noncritical application of geo-
logical form over critically analyzed substance presumes that reservoir models can
be exported from one geological age and setting to another with little concern about
possible differences in reservoir characteristics. All too often, geologists fi nd them-
selves having to explain why the “ look - alike ” failed to predict depositional or dia-
genetic porosity loss, or why structural and stratigraphic models for exploration
prospects did not turn out to be realistic after the drill reached target depth. Analogs
offer comfortable “ sameness ” but they provide no help to explain the unexpected.

They lack information to find hydrocarbon reservoirs in the wide variety of geologi-
cal situations that typify carbonates and they lack information needed to develop

carbonate reservoirs in the most efficient and profi table ways.
This book emphasizes ways to formulate geological concepts rather than “ look -
alikes ” to predict the spatial distribution of porosity and permeability. Optimum
combinations of porosity and permeability and least resistance to fl uid fl ow are

called flow units (the origins of this term are discussed later). When flow units are