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.
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Formation evaluation and well log correlation
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.
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
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
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.
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
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
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.