Page 174 - Introduction to Petroleum Engineering

9

WELL LOGGING

Well logging is an important contributor to formation evaluation. The objectives of
formation evaluation include assessing resource size, supporting the placement of
wells, and interpreting reservoir performance during development. Well logs provide
valuable information about the formation within a few feet of the wellbore. Formation
data can be obtained by examining drill cuttings, core samples, and fluid properties.
Other information can be measured by instruments in a well logging tool that is
lowered into a wellbore. Logging tools can be designed to measure such physical
quantities as electromagnetic and sonic wave signals that pass through a section of
the formation and detect elementary particles emitted by formation rock. The data
are used to estimate formation properties. This chapter introduces the well logging
environment, describes different types of logs, explains why combinations of logs
are used, and discusses techniques and limitations of well log interpretation.

9.1 LOGGING ENVIRONMENT

A well log is produced by lowering an electric logging tool on a cable into a well
and measuring various responses on the instruments as the tool is raised back to the
surface. The tool instruments can measure temperature, wellbore diameter, electrical
resistivity, radioactivity, sonic vibrations, and more. The tool length varies from 40 to
140 ft, depending on the logging plan.

Introduction to Petroleum Engineering, First Edition. John R. Fanchi and Richard L. Christiansen.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/Fanchi/IntroPetroleumEngineering