GLOBE Claritas AVO Processing

AVO Analysis

GLOBE Claritas provides interactive AVO analysis within the sqc application. One or more CDP gathers are displayed at a time, and the user selects the event or time window of interest using the cursor. In a separate window the amplitude variation with offset is plotted, and optionally the variation with offset of the instantaneous amplitude, frequency and phase. The CDP gathers input to this application will usually have been NMO-corrected, and may have had either an Ostrander mix applied, or have been converted from offset to angle gathers with the ANGLE processor module. Alternatively, the ability to define a hyperbolic analysis window on NMO-UNcorrected data can be very useful for avoiding NMO-induced changes in event waveform and frequency.

NMO-corrected CDP gathers may be converted to angle gathers with the ANGLE processor module, which may also be used to create one (or a selection of) constant-angle stacks. The angle gathers are produced by muting and partial stacking, with a choice of linear or curved ray-path algorithms.

The AVOSTACK processor module takes NMO corrected input CDP gathers and outputs AVO attributes as single traces. If angle gathers are input, then AVA attributes are displayed. Available attributes include the AVO intercept (A), AVO slope (B), B*Sign(A), A*B or B/A stacks. Alternatively, the user may request a horizon-based AVO analysis for which the user specifies a digitised horizon file. AVOSTACK then tracks along the specified horizon and outputs the full AVO function as the output "seismic" trace. These traces may then be plotted as a colour-coded section (with CDP and offset/angle axes), giving a complete overview and detailed analysis of a horizon's AVO effect in one display.

In all GLOBE Claritas AVO/AVA analysis the calculation of AVO slope and intercept may be performed either by standard least squares, or a more robust method which is less affected by outliers. AVO analysis of a horizon (in AVOSTACK and SQC) also has the ability to track along the peak or trough of the event.