PNGE 450 EXAM 1 GR Log

Question 1

Introduction

Answer 1

 Gamma Ray log measures the natural radioactivity of the formations.
 GR is a passive measurement and no energy is provided by the logging tool.
 The radioactivity comes from 3 element groups of Uranium, Thorium, and Potassium.
 GR is measured in 2 common ways of natural (total natural radioactivity) and
spectral (identifying the contribution of each 3 source elements of U, Th, K).
 The GR log can be run in combination with practically any tool available.

Question 2

Application

Answer 2

 Correlation
 Indicating the lithology
 Identifying of clay minerals
 Evaluating shale content (volume) of the formation
 Applicable both in open and cased holes.
 Compatible with any type of fluid

Question 3

Origin of Natural GR

Answer 3

 Sedimentary rocks tend to emit Gamma rays.
 Natural GR originates from 3 element groups of
Uranium (
238U), Thorium (232Th), and Potassium (40K)

Question 4

Summary

Answer 4

 GR log measures the natural radioactivity of formation. It can be total or spectral.
 GR log is used for identifying the lithology, clay mineral and evaluating the shale volume.
 GR log is used for well to well (open/cased hole) and core to log correlation.
 GR log requires borehole effect correction.
 GR log is affected by logging speed and time constant. An optimized combination should
be used.