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Methods in Exploration 16: Basic Well Log Analysis, 2nd Edition

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.

Petrophysics and Well Logs

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