AVO Analysis

AVO Attribute Extraction and Analysis

AVO Analysis can be used as a reconnaissance tool to look for AVO anomalies and decide the appropriate approach to quantitative reservoir characterization.

Example

At right is a cross plot of the intercept versus gradient (Shuey 2-term) extracted along a horizon on the section shown below, color coded with time.

A number of points diverge from the trend, indicating a Class-I AVO anomaly.

What this means in terms of rock properties is purely qualitative. However, when looking at a simultaneous inversion result, (the bottom two panels of the section view below) the reason is clear: The Vp/Vs in the layer above the horizon changes dramatically across the anticline.

Using AVO Analysis for reconnaissance followed by the appropriate Jason inversion technique is an efficient way to find and characterize prospects within any seismic survey.

AVO Analysis in the Jason suite

AVO effects on pre-stack CMP gathers provide basic information on the lithology and fluids in the reservoir rocks in your field. Fugro-Jason now offers an AVO attribute extraction application that is integrated with all the other Jason suite applications, allowing you to do a better job of integrating traditional seismic AVO analysis and Jason seismic inversion.

AVO analysis helps in the prediction of reservoir characteristics away from well control points. Reliable estimation of petrophysical parameters is needed as input for such studies. These petrophysical estimates are an integral part of advanced reservoir characterization and modeling. Fugro-Jason also offers the PowerLog® and RPM set of integrated petrophysics/rock physics applications to support the petrophysical modeling needed for robust AVO analyses.

Creating synthetic offset gathers using well logs and petroelastic parameters from PowerLog RPM indicates what kinds of AVO anomalies may be present in the data. This is done with Jason Well Tie using synthetic wavelets.With the Estimate Wavelets extension to Well Tie, the specific wavelet from the seismic data can be used for even more accurate modeling.

Starting with NMO-corrected gathers, you can use the AVO Analysis module to make a first pass scan to detect amplitude anomalies, as well as make an estimation of the contrast of the seismic and elastic properties of the rocks.

The following attributes are offered:

Intercept and gradient (Shuey 2-term)
Intercept, gradient and far offset (Shuey 3-term)
Vp and Vs contrast (Smith & Gidlow)
Zp and Zs contrast (Fatti et. al)
Bulk- and Shear – modulus and density contrast (Cray et. al).

Mute, taper, stabilization, and filter functions are included to ensure robust results.

Input NMO gathers and Shuey 2-term intercept and gradient results. Background color is the P-Velocity trend used for angle-offset conversions.