3-D AVO analysis
The ultimate goal in seismic interpretation is to derive a reservoir model. The geometry of the reservoir model is provided by structural interpretation (interpretation of 3-D seismic data), the result of which is downscaled in the vertical direction and upscaled in the lateral direction to build the structural framework of the reservoir model. This means that the reservoir layer is sliced into layers as thin as 1 m in the vertical direction, and each thin layer is compartmentalized into cells with lateral dimensions as big as a few hundred meters.
The internal constitution of the reservoir layer itself is specified by using the result of a stratigraphic interpretation (interpretation of 3-D seismic data). The interior of the reservoir layer eventually needs to be populated by the petrophysical properties, such as porosity, permeability, and fluid saturation. When derived from 3-D seismic data, AVO attributes can be used to infer these properties within the reservoir zone in inline, crossline, and vertical directions.
The prestack signal processing sequence tailored for AVO analysis described in this section is applicable directly to 3-D seismic data. To generate the CRP gathers used in prestack amplitude inversion to derive the volume AVO attributes, however, you need to follow the workflow for 3-D prestack time migration (3-D prestack time migration). Figures 11.2-44 and 11.2-45 show the gradient and intercept volumes, respectively, derived from the CRP gathers as in Figure 7.4-21, following the application of opacity removal. While the opacity test applied to the image volume as shown in Figure 7.5-33 enabled us to identify the presence of a channel system within the reservoir zone, the opacity tests applied to the attribute volumes shown in Figures 11.2-44 and 11.2-45 indicate characteristics of fluid distribution within and away from the channel. This information is needed to choose the most desirable drilling locations and thus better manage the development of the reservoir. Note from Figure 11.2-45b that the amplitudes labeled in red that define the channel also are present along one of the faults. This suggests that the fault may represent the migration path for fluids. Also note the presence of a red spot at the center of the channel between the two faults. This may represent a thicker zone in the flood plain.
Figure 7.4-21 Selected common-reflection-point (CRP) gathers from 3-D prestack time migration of the data as in Figures 7.4-16, 7.4-17, and 7.4-18.
- Analysis of amplitude variation with offset
- Reflection and refraction
- Reflector curvature
- AVO equations
- Processing sequence for AVO analysis
- Derivation of AVO attributes by prestack amplitude inversion
- Interpretation of AVO attributes