1. University of Kerala, India.
Exploration Geology
Well Logging
Omer M. Ahmed
MSc, 2ed Year, 2016
University of Kerala, India.

2. Introduction Petrophysic of the rocks
It is the study of the physical and chemical properties of the rocks related to the pores and fluid distribution
Porosity, is ratio between volume of void to the total voids of the rock.
Permeability, is ability of a porous material to allow fluids to pass through it.
Electric, most of the sedimentary rocks don’t have conductivity.
Radiation, clay rocks have 40K, radiate alpha ray.
Hardness, it depends on the cementing material and thickness of the sediments.

3. WELL LOGGING
The systematic recording of rock properties and it’s fluid contents in wells being drilled or produced to obtain various petrophysical parameters and characteristics of down hole sequences (G.E Archie 1950).
The measurement versus depth or time, or both, of one or more physical properties in a well.
These methods are particularly good when surface outcrops are not available, but a direct sample of the rock is needed to be sure of the lithology.

4. A wide range of physical parameters can be measured.
In some cases, the measurements are not direct, it require interpretation by analogy or by correlating values between two or more logs run in the same hole.
Provide information on lithology, boundaries of formations and stratigraphic correlation.
Determine Porosity, Permeability, water, oil and gas saturation.
Reservoir modeling and Structural studies… etc.

5. Types of Well Logging
Logs can be classified into several types under different category
Permeability and lithology Logs
Gamma Ray log
Self Potential [SP] log
Caliber log
Porosity Logs
Density log
Sonic log
Neutron log
Electrical Logs
Resistivity Log

6. Permeability
and
lithology
Log

7. Gamma Ray Log (GR)
Measures the radioactivity of the formation and evaluation of radioactive minerals, such as potassium and uranium deposits in clay rocks, like shale.
Gamma ray penetrates steel, so the log can be run in cased holes.
The log has robust lithostratigraphic indicator that can be used for correlation and facies studies.
Unaffected by fluids
Evaluation of shale content.

8. Sand GR Log Scale 0 ------- 150
The base line (shale line) is center line = 75
100
Clay
Permeable zone
150
200
Sand
----
Depth (M)

9. Evaluation of the shale content
Where; V(sh)= shale volume (%), GR(log)= GR value from log, GR(max)=GR value from log at shale line, GR(min)= GR value from log at sand line

10. Spontaneous Potential (SP) Log
Measuring the difference in electrical potential between two electrodes, a grounded electrode and an electrode on the sonde (logging tool).
The SP log is very similar in shape to GR log (but does not identify thin beds), and both can be used alternatively for correlation purposes.
If the fluid is better conductor than the drilling mud (salt water), the curve will deflect to the left.
If the fluid is poor conductor (fresh water or oil), it will deflect to the right.

11. SP Log Scale, 1 line = 20 mV The base line = 0 Friable rock
Fresh water
Clay
Hard rock
Saline water
Not clay

12. Caliber Log
The logging system provides a continuous recording of borehole diameter versus depth.
Can be used in both soft and hard formations, run in uncased wells.
The main indicator of the log is:
Determine hole and casing diameter,
Locate caved zones,
Recognition of mud cake
When a hole diameter less than the bit size is an excellent indicator of permeability.

13. Caliper log Base line is bit size Friable rock Hard rock
permeable zone

14. Determine the porosity,
Porosity Log
Determine the porosity,
And
Type of fluids

15. Density Log
The log measures the bulk density of the formation, by tool contains a radioactive source emitting gamma rays.
Measure how much radiation returns to a sensor and that controlled by rock density, porosity, composition of the formation and fluids.
The main use of the Log is to determine a value of porosity.
It s also useful in the detection of gas-bearing formations and recognition of evaporites.

16. Density Log
Scale = 0.1
Add the value from left to right
Or subtract from right to left

17. Sonic (acoustic) Log
Is a continuous record of the specific time required versus depth for a compressed wave to travel through a given distance of formation in the borehole. (ms/ft.) or (s/ft.)
The acoustic travel time in a formation depends upon lithology and porosity, the more dense the lower the travel time (∆t) because sound waves travel through the rock it self rather than the mud
The main uses, is estimation of porosity (primary) and the calibration of regional seismic data.

18. Common lithological travel time

19. Sonic Log ∆t log = Reading from sonic log in µs/ft
∆t ma =Transit time of matrix material
∆t f = fluid velocity ~189 s/ft.

20. Neutron Log
The log design from the fact, hydrogen atom is consist of proton and electron so it is very needful to the neutron.
Using a radioactive source emitting neutrons which is collide with the hydrogen nuclei of the formation material.
The amount of returning radiation will show the total of the lost, a dry layer will reject all the neutron and if it is contain a fluids the lost will be more.
Most of the gas field discovered by the neutron Log (when the density is low compare with other Logs for the water and oil).

21. Neutron Log Displayed as (NPHI, PHIN, NPOR)
For the limestone porosity is direct from the log
EX: 14%
Whereas other lithology is from the other chart

23. Electrical Logs EX: Resistivity Log For determine water and
Hydrocarbons

24. Electrical Logs
Are the most important tools available and first logs to be used by Marcel and Conrad Schlumberger 1927
Widely used in exploration work for water, minerals , hydrocarbons and engineering purposes.
The main use of the electrical tools is to calculate
The water saturation of a reservoir formation
Electrical conductivity or resistivity of the materials
And give an idea about hydrocarbon.

25. Resistivity Log
Resistivity of the material is resistant in ohms of a unit cube, (ohms/S) or (ohms/M)
Most of the rocks are porous and moisture (sandstone), and other are compacted which they are containing moisture in the component minerals (granite)
Resistivity decrease with increase in the moisture content and for rock with low moisture content resistivity determined by the component minerals.
Weathered rocks has lower resistivity than fresh.

26. Types of Resistivity 1/ Micro for saturated zone
2/ Shallow for transition zone
3/ Deep for the zone which is not effected by drilling mud

27. Resistivity Log M<S<D Saline water M>S>D Fresh water
Micro: red Deep: black Shallow: blue
M<S<D
Saline water
M>S>D
Fresh water
M<S<<D
Petroleum
Dry layer when they shows overlap between them
When the D and M only overlapping that give an idea about the reservoir

28. CONCLUSION
Depending on the Petrophysic of the rocks different type of logging have been used for determine different properties , porosity,
The importance thing in the log is heading and base line.
Combinations of two or more logs better than one log for determine lithology, porosity, and hydrocarbon content.

29. REFERENCES
Andrew D. Miall (2016), Stratigraphy: A modern Synthesis, Springer International Publishing Switzerland, 454 P.
Baker Hughes INTEQ (2001), Advanced Wireline & MWD Procedures Manual, Baker Hughes INTEQ Technical Publications Group, 192P.

30. Thank
You
Thank
You