Modeling AVO Classes

Feby Hapsari

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Rutherford/Williams Classification

Rutherford and Williams (1989) derived the following classification 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 change Class 3: Low impedance sand with increasing AVO Class 4: Low impedance sand with decreasing AVO

This document describes modeling of the gas sand AVO classes and the derived AVO attributes for both positive and reverse polarity wavelets.

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This figure from Castagna et al (1998) illustrates 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 2.291010 3220 1620 2.352000 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 2.291010 2800 1620 2.28 1010 3000 1620 2.32000 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 2.291010 2540 1620 2.09 1010 2540 1120 2.392000 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

Class 1

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Class 1

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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

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Support Offices

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