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x Preface

selecting gas and liquid flow rates. Chapter 10 provides guidelines for
underbalanced drilling operations.
Since the substance of this book is virtually boundless in depth,
knowing what to omit was the greatest challenge. The authors believe
that it requires many books to describe the foundation of knowledge in
drilling circulation systems. To counter any deficiency that might arise
from space limitations, this book provides a reference list of books and
papers at the end of each chapter so readers can consult other sources of
information about the topics discussed.
As for presentation, this book focuses on providing and illustrating
engineering principles used for designing and optimizing drilling circula-
tion systems, rather than on discussion of in-depth theories. Derivation of
mathematical models is beyond the scope of this book. Applications of the
principles are illustrated by solving example problems. While the solutions
to some simple problems that do not involve iterative procedures are
demonstrated with stepwise calculations, complicated problems are solved
with computer spreadsheet programs, some of which can be downloaded
from the publisher’s website. The combination of the book and the
computer programs creates the perfect tool kit for drilling engineers for
performance of their daily work in the most efficient manner. All of the
computer programs were written in the form of spreadsheets in MS Excel
that are available in most computer platforms in the oil and gas industry.
These spreadsheets are accurate and very easy to use. While both U.S. field
units and SI units are used in the book, the option of using U.S. field units
or SI units is provided in the spreadsheet programs.
This book is based on numerous documents, including reports and
papers accumulated through years of work at the University of Louisiana
at Lafayette and at Pegasus Vertex, Inc. The authors are grateful to the
university and the company for permission to use these materials. Special
thanks go to Chevron USA for providing professorships in petroleum
engineering throughout the editing of this book. Our thanks also go to
Mr. Guoqiang Yin of Shell USA, who contributed a thorough review
and edit of this book. On the basis of the collective experiences of the
authors and of reviewers, we expect this book to be of great value to
drilling engineers in the oil and gas industry.
Dr. Boyun Guo
Chevron Endowed Professor in Petroleum Engineering
University of Louisiana at Lafayette