This document provides an overview of well log formation evaluation and interpretation. It discusses the basic well log tools used to measure parameters like gamma ray, resistivity, density, and neutron porosity. It describes qualitative log interpretation to identify reservoir zones, hydrocarbon-bearing zones, and fluid types. The document also covers quantitative interpretation, including calculating porosity, water saturation, and estimating hydrocarbon reserves. In conclusion, well logs provide key information for establishing the existence of producible oil and gas reservoirs, including reservoir type, thickness, porosity, permeability, and fluid saturation.

1. Formation evaluation
and well log correlation
SWAPNIL PAL
IMT GEOLOGICAL TECHNOLOGY
INDIAN INSTITUTE OF TECHNOLOGY ROORKEE

2. Overview
Well log definition and its importance
Fundamentals of qualitative and quantitative log interpretation
Formation evaluation with well logs
Processing and interpretation of well log data
Conclusion

3. Well log
The continuous recording of
a geophysical parameter
along a borehole produces a
geophysical well log.
The value of the
measurement is plotted
continuously against depth
in the well.

4. Basic Logs Tools and their
Measurements
Gamma Ray log

5. Basic Logs Tools and their
Measurements
Calliper log

6. Basic Logs Tools and their
Measurements
Electrical log

7. Basic Logs Tools and their
Measurements
Density log

8. Basic Logs Tools and their
Measurements
Neutron log

9. Petrophysical Interpretation
Qualitative assessment Quantitative assessment
Assessment of reservoir
properties, fluid type form
log pattern.
Numerical estimation of
reservoir properties viz. % of
oil, water etc.

10. Basic steps for quick look evaluation
ROCK
Reservoir
Non-Reservoir
Hydrocarbon
bearing
Water bearing
Gas bearing
Oil bearing

11. Qualitative Interpretation
Identification of Reservoir or Non-reservoir
Low gamma ray
(Reservoir rock)

12. Identification of hydrocarbon or water bearing zone
Qualitative Interpretation
Low gamma ray
+
High Resistivity value

13. Qualitative Interpretation
Low gamma ray
+
High Resistivity value
+
Large deviation in RHOB and NPHI value
(cross-over region)
Identification of oil or gas bearing zone

14. Qualitative Interpretation
Gas bearing zone
Oil bearing zone
Water bearing zone

15. Quantitative Interpretation
 Estimation of effective porosity & permeability.
 Estimation of volume of clay fraction.
 Estimation of hydrocarbon saturation.
 Determination of the depth and thickness of net
pay.
 Estimation of reserves of hydrocarbon.

16. Quantitative Interpretation
Estimation of porosity

17. Quantitative Interpretation
Estimation of porosity
Depth (m) Vsh PHID PHIdc PHIN PHInc
effective
(Gas)
1940 0.710526 0.278788 0.106539 0.46 0.175789 0.145349
1945 0.078947 0.418182 0.399043 0.09 0.058421 0.285174
1948 0.052632 0.381818 0.369059 0.07 0.048947 0.263249
1950 0.039474 0.424242 0.414673 0.06 0.044211 0.29488
1953 0.039474 0.484848 0.475279 0.14 0.124211 0.34736
1957 0.697368 0.327273 0.158214 0.33 0.051053 0.117554
1958 0.644737 0.266667 0.110367 0.41 0.152105 0.132885
gas bearing zone

18. Quantitative Interpretation
Estimation of porosity
Depth (m) Vsh PHID PHIdc PHIN PHInc
effective
(Gas)
1970 0.657895 0.236364 0.076874 0.36 0.096842 0.086858
1972 0.644737 0.218182 0.061882 0.325 0.067105 0.064494
1974 0.118421 0.272727 0.244019 0.19 0.142632 0.193325
1976 0.460526 0.272727 0.161085 0.34 0.155789 0.158437
1978 0.276316 0.254545 0.18756 0.22 0.109474 0.148517
1980 0.434211 0.272727 0.167464 0.275 0.101316 0.13439
1982 0.263158 0.284848 0.221053 0.24 0.134737 0.177895
1984 0.723684 0.254545 0.079107 0.43 0.140526 0.109817
oil bearing zone

19. Quantitative Interpretation
Estimation of porosity
Depth (m) Vsh PHID PHIdc
2025 0.236842 0.278788 0.212759
2028 0.565789 0.230303 0.1
2029 0.328947 0.212121 0.142344
2030 0.276316 0.260606 0.188596
2031 0.342105 0.242424 0.15949
2034 0.394737 0.278788 0.16874
2035 0.223684 0.260606 0.202313
2036 0.223684 0.260606 0.202313
2037 0.197368 0.236364 0.189713
water bearing zone

20. Quantitative Interpretation
Estimation of hydrocarbon saturation
Can not be measured directly but inferred from determination of
WATER SATURATION (Sw) from RESISTIVITY and POROSITY logs.
• Sw – Fraction of pore space occupied by water.
• Sh – Fraction of pore space occupied by hydrocarbon.
Sh + Sw = 1
Oil
Water

21. Quantitative Interpretation
Archie’s equation

22. Quantitative Interpretation
Calculation of formation water resistivity : Rw
Using Inverse Archie’s equation
Rt
0.95
0.7
0.1
0.8
0.9
0.7
0.7
0.7
0.85
Rw
0.073837
0.037128
0.0045
0.054332
0.052893
0.054406
0.047541
0.047541
0.047488
Depth
2025
2028
2029
2030
2031
2034
2035
2036
2037
Water bearing zone
Rw= 0.05, this is used in Archie’s equation to calculate water
saturation in oil and gas bearing zone

23. Quantitative Interpretation
Depth
1940
1945
1948
1950
1953
1957
1958
1970
1972
1974
1976
1978
1980
1982
1984
PHId
0.278788
0.418182
0.381818
0.424242
0.484848
0.327273
0.266667
0.236364
0.212121
0.272727
0.272727
0.254545
0.272727
0.290909
0.254545
Rt
0.65
15
35
48
33
0.9
0.85
1
1.5
2
4
2.9
3
1.2
0.8
Sw (Archie)
0.994843
0.138062
0.098991
0.076076
0.080283
0.720201
0.909509
0.946029
0.860707
0.579751
0.409946
0.515847
0.473365
0.701677
0.982143
Calculation of water saturation in oil and gas zones
0
0.2
0.4
0.6
0.8
1
1.2
1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990
Sw:watersaturation
Depth (m)

24. Qualitative Interpretation
Gas bearing zone
Oil bearing zone
Water bearing zone
0
0.2
0.4
0.6
0.8
1
1.2
1930 1940 1950 1960 1970 1980 1990
Sw:watersaturation
Depth (m)
Hurray!
Oil found!!
V/s
Quantitative Interpretation

25. Conclusion
Well logs contains key information about the formation drilled in
different petro-physical measurements. i.e.
 Prospective zones of hydrocarbon.
 Reservoir type and thickness.
 Estimation of Porosity, permeability.
 Fluid type present in the pores and saturation level.
To economically establish the existence of producible
hydrocarbon reservoirs (oil & gas).

26. References
Archie II: Electrical conduction in hydrocarbon bearing zone. (n.d.). In Rock Physics (Vol.
36).
Archie III: Electrical conduction in shaly sand. (n.d.). In Rock Physics (Vol. 1).
Archie's law: Electrical conduction in clean, water bearing rock. (n.d.). In Rock
physics/History (Vol. 36).
Halliburton. (n.d.). Log Interpretation Charts.
M H Rider. (1991). The Geological Interpretation of well logs. Glasgow: Whittes Publishing.
(1989). Open hole well logging Interpretation. Texas: Schlumberger Wireline & Testing.
Serra, O. (1984). Fundamentals of well log interpretation. Amsterdam: Elsevier.

27. Thank you