Wireline logging: Resistivity log

Resistivity logging presentation prepared by me to present in a class.

1. Wireline Logging and Hydrocarbon Exploration Presented by Ziaul Haque Department of Geology and Geography Auburn University Auburn, Alabama, USA

2. Outline: Part-I Wireline logging Why logging Types of logging Uses of different logs History of logging. Tools Resistivity logs Part-II Resistivity logs. Caliper logs Caliper logs tools Uses of caliper logs and Resistivity Logs Hydrocarbon determination .

3. Wireline Logging Continuous recording of a geophysical parameter along a borehole. The value of the measurement is plotted continuously against depth in the well. May represent over 4 kilometers of readings continuously.

4. T hings to remember: Why logging? Sampling during drilling ( cutting sampling) is imprecise recording of the formations encountered. The results of coring is very precise and unequivocal but this is slow and expensive. Logs fill the gaps between ‘cuttings’ and ‘cores’, and with experience, calibration and computers, they can almost replace cores . Logging is precise but equivocal; needs high level of geological and petrophysical experiences. A single log never tells about the subsurface condition. To identify the subsurface condition with certain degree of confidence we need at least three different types of log .

5. History of logging: In 1919 Conrad Schlumburger first use logging measurement for hydrocarbon determination.

6. Logging Tools: Schematic Diagram of Wireline Well-Logging Sonde

7. Uses of wireline logs:

8. Resistivity Log Off all the logging tools resistivity is the most archetypal. It was with resistivity measurements that Conrad Schlumberger started his company in 1919. The resistivity log is a continuous plot of a formation’s resistivity from the bottom of the well. Measures the resistance to the passage of electric current. Measured by resistivity tools.

9. Resistivity Logging Principle: Most rock materials are essentially insulators. Formation fluids that enclosed the rocks material is conductors. Hydrocarbons are the exception to fluid conductivity. So when a formation is porous and contains salty water the overall resistivity will be low and when the same formation contains hydrocarbons, its resistivity will be high .

10. Formation R esistivity Factor (F): Although rock plays no active role but it has passive role in the resistivity or conductivity. The passive role is basically dependent on rock texture or more specifically on the geometry of the pores and pore connection. Schematic illustration of three formations which have the same porosity b ut different value of F.

11. Next Class: Resistivity Measurement tools. Resistivity profiling. Resistivity of fine grained material. Caliper logging. Caliper log tools. Uses of resistivity and caliper logs Hydrocarbon determination.

12. Questions?

13. Thank You All For Your Attention

14. Review of Part-I

15. Wireline Logging Continuous recording of a geophysical parameter along a borehole. The value of the measurement is plotted continuously against depth in the well. May represent over 4 kilometers of readings continuously.

16. Resistivity Log The resistivity log is a continuous plot of a formation’s resistivity from the bottom of the well. Measures the resistance to the passage of electric current. Measured by resistivity tools.

17. Part-II Resistivity logs. Caliper logs Caliper logs tools Uses of caliper logs and Resistivity Logs Hydrocarbon determination .

18. Resistivity Measurement tools: The basic circuitry of the resistivity tools was established by the Conrad Schlumberger in 1927. Current electrode passed current through the formation and the potential drop is measured between two potential electrodes. Two types of resistivity tools are used: Focused (Modern) and Non focused.

19. Resistivity Profiling at different depth:

20. Types of resistivity tools are used to measure resistivity in different zones surrounding the borehole:

21. Why fine grains (Shale) material shows low resistivity: Rocks plays passive role in the resistivity or conductivity its not always true. When shale is present it plays an active role in conductivity and F is no longer constant. Clays conduct electricity in two ways, through pore water and through the clay itself. Clay is like an inverted electric cable; the inside is non-conductive while the outside is conductive.

22. Caliper tools measure hole size and shape. The simple mechanical caliper measures a vertical profile of hole diameter. The more sophisticated geometry tools records two simultaneous calipers and give an accurate borehole shape and orientation.

23. Uses of Resistivity Log: There are two types of use: 1.Quantitative use: Hydrocarbon saturation measurement 2. Qualitative use: Textures. Gross Lithology. Correlation. Facies identification. Compaction, Shale porosity and 0verpressure.

24. Qualitative Uses of Resistivity Log : Lithology

25. Qualitative Uses of Resistivity Log : Correlation

26. Qualitative Uses of Resistivity Log : Overpressure

27. Hydrocarbon Identification: Negative separation: a good indicator of presence of hydrocarbon. Fig: Resistivity over the gas/oil bearing zone. MSFL shows very low resistivity in the flushed zone(mud fluid resistivity),LLS shows a little higher resistivity(transition zone resistivity) and LLD shows very high resistivity(resistivity of virgin area).