Formation evaluation (or well log analysis or petrophysics) is
at the intersection of a number of disciplines, including, but
not limited to, geology, geophysics, and reservoir engineering.
Each discipline that encounters and uses well log data does
so from its own perspective. In doing so, each discipline
sometimes uses the data without a full understanding of how
the measurements are made.
That incomplete understanding can encompass the
processing of the actual measurements into the raw
data provided by the data logging companies and to the
interpretation methods that convert that data into usable
information about the subsurface. It is this incomplete
understanding of well log data that commonly produces
conflicting interpretations from different sources, when the
goal should be a single cohesive model of the subsurface that
can be consistently applied by all disciplines.
This book is a revision of George Asquith’s Basic Well
Log Analysis for Geologists, one of the most popular
books published by the AAPG. This second edition does
not claim to provide all information about well logs from
all perspectives. Like the original publication, it remains
focused on the interpretation of basic, or common, openhole
logging measurements. It also remains focused on the
traditional interpretive goals of formation porosity, fluid
saturation, and lithology.
The first chapter of this volume provides a general introduction
to well logging principles and methods that will be used
throughout the remainder of the book.
Chapters 2 through 6 introduce specific log types and discuss
how different log types measure various properties in the
wellbore and surrounding formations, what factors affect these
measurements, where on a standard log display a particular
curve is recorded, and how interpreted information is obtained
from the logs using both charts and mathematical formations.
Unlike many other logging texts, the logging tools are grouped
according to their primary interpretation target, rather than their
underlying measurement physics.
Spontaneous potential (SP) and gamma ray logs are
discussed first, as their primary use is correlation and their
primary interpretive target is gross lithology (the distinction
between reservoir and
nonreservoir). The
porosity logs (i.e., sonic,
density, and neutron) are
covered next, then the
resistivity logs. Nuclear
magnetic resonance
logs, although they
provide porosity (among
other quantities of
interest), are presented
after resistivity logs.
The final four chapters
deal with interpretation
of the data, in detail
with example problems
and their solutions. These chapters bring the introductory
material of Chapter 1 together with the specific measurement
information and are intended to provide a coherent view of the
interpretation process.
Accompanying this book is a CD. The CD contains digital
versions of the data from the case studies, a summary
guide to the measurements and their interpretation, and a
simple spreadsheet containing some of the more common
interpretation algorithms.
Updated, this Basic Well Log Analysis, 2nd Edition, is a general
introduction to common openhole logging measurements, both
wire line and MWD/LWD, and delivers a great impact on training
and self-training along with superior workbook exercises,
newer measurements, borehole imaging, and nuclear magnetic
resonance in separate chapters, all directed to provide a guide
through the lengthy and sometimes ambiguous terminology
of well logging and petrophysics. It provides readers with
interpretation examples and solutions, so that the techniques
described in this volume can be practiced.