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Modeling AVO Classes
This document describes modeling of the gas sand AVO classes and thederived AVO attributes for both positive and reverse polarity wavelets.
Feby HapsariVHR Jakarta - October 2006
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Rutherford/Williams Classification
Rutherford and Williams (1989) derived the following classif ication scheme for AVO
anomalies, with further modifications by Ross and Kinman (1995) and Castagna(1997):
Class 1: High impedance sand with decreasing AVO
Class 2: Near-zero impedance contrast
Class 2p: Same as 2, with polarity changeClass 3: Low impedance sand with increasing AVO
Class 4: Low impedance sand with decreasing AVO
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This figure from Castagna et
al (1998) il lustrates all 5 of
the gas sand AVO classes.
Gas Sand AVO Classes
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Depth (m) P-wave (m/s) S-wave (m/s) Density (g/cc)
0 2900 1330 2.29
1000 2900 1330 2.29
1010 3220 1620 2.35
2000 2900 1330 2.29
Class 1
Depth (m) P-wave (m/s) S-wave (m/s) Density (g/cc) Depth (m) P-wave (m/s) S-wave (m/s) Density (g/cc)0 2900 1330 2.29 0 2900 1330 2.29
1000 2900 1330 2.29 1000 2900 1330 2.29
1010 2800 1620 2.28 1010 3000 1620 2.3
2000 2900 1330 2.29 2000 2900 1330 2.29
Depth (m) P-wave (m/s) S-wave (m/s) Density (g/cc) Depth (m) P-wave (m/s) S-wave (m/s) Density (g/cc)0 2900 1330 2.29 0 2900 1330 2.29
1000 2900 1330 2.29 1000 2900 1330 2.29
1010 2540 1620 2.09 1010 2540 1120 2.39
2000 2900 1330 2.29 2000 2900 1330 2.29
Class 4
Class 2 Class 2p
Class 3
The model was a 10 m thick sand at 1000 m depth. The data used for creating simple 3-
layer models is as shown:
Data
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Class 1
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Class 1
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Class 2
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Class 2
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Class 2p
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Class 2p
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Class 3
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Class 3
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Class 4
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Class 4
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Positive Polarity A*B Product
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Reverse Polarity A*B Product
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Positive Polarity SPR
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Reverse Polarity SPR
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Positive Polarity Rs
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Reverse Polarity Rs
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Positive Polarity Fluid Factor
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Reverse Polarity Fluid Factor