This document discusses principles of well logging. It describes how well logging aims to evaluate subsurface hydrocarbon accumulations through measuring properties in boreholes. It outlines different types of hydrocarbon traps and elements in a petroleum system. It then explains what a well log is and different types of logs used, including gamma ray, resistivity, sonic, and neutron logs. Gamma ray logs specifically measure natural radioactivity to distinguish between lithologies like sandstone and shale. The document provides details on interpreting gamma ray logs and calculating shale volume from gamma ray readings.

1. Principles of well logging
Asst. Lecturer : Amir I. Abdelaziz
geo.amir@hq.helwan.edu.eg

2. Lab. 1 : Well logging principles
Well planning and execution

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Aim of well logging
Evaluation of subsurface hydrocarbon accumulations
Gas
Oil
Water

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Hydrocarbon Traps
• Structural
•Stratigraphic
•Mixed

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Petroleum System Processes
24803
Petroleum System ElementsPetroleum System Elements
120° F120° F
350° F350° F
GenerationGeneration
MigrationMigration
Seal RockSeal Rock
Reservoir
Rock
Reservoir
Rock
OilOil
WaterWater
Gas
Cap
Gas
Cap
EntrapmentEntrapment

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What is a log?
Well log is a continuous record of measurement
made in bore hole that respond to variation in
some physical properties of rocks through which
the bore hole is drilled.

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Log acquisition

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Log acquisition – types of logs
• Geophysical Logs
– Gamma Ray
– Resistivity
– Sonic
– Neutron
– Density
– Dip Meter
– Borehole Imaging
• Production Logging
– Pressure
– Temperature
– Spinner
– Fluid Density
• Well Inspection
– Caliper
– Electro-magnetic
– Ultrasonic
– RA Tracer
– Video

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The borehole environment

13. Lithology Logs
Gamma Ray
• Measures Natural radioactivity
• Main radioactive elements:
– Potassium
– Thorium
– Uranium
• K and TH mostly in shales
U from other sources
• Primary use a a basic lithology
indicator (sand/shale)

14. Lab. 1 : Gamma Ray log
1- Records radioactivity of a formation
2- Shales have high gamma radioactive response
3- Gamma ray logs are most commonly used logs for sequence stratigraphic analysis.
4- Gamma Rays are high-energy electromagnetic waves which are emitted by atomic nuclei as a form of radiation.
5- Gamma ray log is measurement of natural radioactivity in formation versus depth.
6- It measures the radiation emitting from naturally occurring U, Th, and K.
7- It is also known as shale log.
8- GR log reflects shale or clay content.
9- Clean formations have low radioactivity level.
• Correlation between wells,
• Determination of bed boundaries,
• Evaluation of shale content within a formation,
• Mineral analysis,
GR log can be run in both open and cased hole
All rocks contain some radioactive material,
although marine shales have a higher gamma
ray emission level than sandstone, limestone
and dolomite. This difference makes the
gamma ray log especially useful for
distinguishing shales from non shales,
therefore the gamma ray is essentially a
lithology log.

15. Shale volume
Shale
Sand
Shale
Shale
Sand
1) Pick a clean GR response
GR 90 -> Vsh = 55%
0 150api
2) Pick a shale GR response
3) Scale between
35
90
GR log - Grclean
Vsh =
GR shale - Grclean
135

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