Well loggining. Gamma Ray log

Bore hole, Mud circulation and gamma ray log

1. Principles of well logging
Asst. Lecturer : Amir I. Abdelaziz
[email protected]

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

3. Lab. 1 : Well logging principles
Aim of well logging
Evaluation of subsurface hydrocarbon accumulations
Gas
Oil
Water

4. Lab. 1 : Well logging principles
Hydrocarbon Traps
•Structural
•Stratigraphic
•Mixed

5. Lab. 1 : Well logging principles
Petroleum System Processes24803
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

6. Lab. 1 : Well logging principles

7. Lab. 1 : Well logging principles
Whatisalog?
Welllogisacontinuousrecordofmeasurement
madeinboreholethatrespondtovariationin
somephysicalpropertiesofrocksthroughwhich
theboreholeisdrilled.

8. Lab. 1 : Well logging principles
Log acquisition

9. Lab. 1 : Well logging principles
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

10. Lab. 1 : Well logging principles

11. Lab. 1 : Well logging principles

12. Lab. 1 : Well logging principles
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 abasic 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

16. Lab. 1 : Well logging principles

17. Lab. 1 : Well logging principles

18. Lab. 1 : Well logging principles

19. Lab. 1 : Well logging principles

20. Lab. 1 : Well logging principles