AVO on stacked gathers

Hi there,

I was wondering if someone out there is using stacked gathers to do AVO analysis, if so how is it different from using Pre-Stacked gathers, what are the implications in terms of its intepretation, can someone boldily make any sensible conclusion in terms of fluids in the reservoir from this study?

Please refer me to right articles for more info.

Okay - an old post, but one with no reply.

You can only do AVO or AVA analysis on unstacked data - that is to say gathers, before they are stacked.

This is because you need to have offsets (AVO) or angles (AVA) available for these analysis techniques - they use the fact that the amplitude of the seismic reflection will vary with angle (based on the Zeoppritz equations) which might give you detectable variations that can be used to predict oil or gas. In AVO analysis they are approximating the angle with offset.

When you stack the data, you add up all the traces in the pre-stack gather, usually after correcting them to zero offset (via NMO correction or pre-stack migration); as such you don't have a gather any more, just stacked traces.

The stacked traces don't have any offset or angle information any more - so AVO and AVA analysis is not possible.

You can use other techniques with stacked data - such as acoustic or elastic impedance inversion.

It is also possible to *partially* stack the data into a series of "offset limited stacks" - or more commonly "angle stacks"; these are usually used for "AVO reconnaissance" as you can compare the nears (angles /offsets) to the fars (angle offsets) and look for differences that show an AVO/AVA anomaly for further investigation.

Yes,
AVO/ AVA is on unstacked data.
Only partly stacked data i.e. near angle stack, far angle stack and mid angle stacks are used
in AV analysis.
Just to ignite something: Sometimes near and far angle stacks are
subtracted to confirm class II anomaly with polarity reversal.

Rajesh Madan