Amplitude versus offset (AVO) analysis is a relatively new seismic technique used very successfully to predict hydrocarbon (especially gas) and the lithology for oil exploration and reservoir characterization. This method is using the AVO technique seismic amplitudes and their variation as a function of offset are analyzed. This information is then used to predict the lithology and fluid content.
The basic concept behind the AVO technique is the analysis of the reflection process. We take advantage of the fact that the measured amplitude is related to the strength of the reflection (reflection coefficient), and that the reflection coefficient depends on three parameters:
- Change in P-wave velocity across the interface.
- Change in S-wave velocity across the interface.
- Change in density across the interface.
To understand AVO technology it is important to have an understanding of how: rock parameters (lithology, porosity, fluid content) affect seismic rock properties (Vp and Vs), the reflection process reacts to changes in seismic rock parameters, to process seismic data, to obtain amplitudes that are proportional to reflect the coefficients, to invert seismic amplitude, to be the seismic rock parameters, to interpret these results and to obtain the analysis of lithology, porosity, and fluid content.
AVO analysis is one of the methods that is used in advance of processing analysis. AVO is standing for either as Amplitude Versus Offset or Amplitude Variation with Offset. It is used to determine where is gas – sand area by cross-plotting between amplitude versus offset. We can see the relation between different amplitude and different angle, and after that we can determine which zone is gas – sand area by knowing their classification.