Well loggining. Gamma Ray log

Principles of well logging

Asst. Lecturer : Amir I. Abdelaziz

[email protected]

Lab. 1 : Well logging principles

Well planning and execution


Aim of well logging

Evaluation of subsurface hydrocarbon accumulations

Gas

Oil

Water


Hydrocarbon Traps

• Structural

•Stratigraphic

•Mixed


Petroleum System Processes

24803

Petroleum System ElementsPetroleum System Elements

120° F120° F

350° F350° FGenerationGeneration

MigrationMigration

Seal RockSeal Rock

Reservoir RockReservoir Rock

OilOil

WaterWater

Gas CapGas Cap

EntrapmentEntrapment



What is a log?

Well log is a continuous record of measurementmade in bore hole that respond to variation insome physical properties of rocks through whichthe bore hole is drilled.


Log acquisition


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



Lab. 1 : Well logging principlesThe borehole environment

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)

Lab. 1 : Gamma Ray log1- Records radioactivity of a formation2- Shales have high gamma radioactive response3- 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.

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 - Gr clean

Vsh =

GR shale - Gr clean

135






Well loggining. Gamma Ray log

Science