Seismic response
The Seismic response wizard models synthetics and amplitude variation with angle (AVO) from well logs. Compare the Original with fluid-substitution scenarios to assess amplitude changes, event time shifts, and intercept–gradient behavior. These are modelled responses, not measured seismic.
Launching the wizard
On the Petrophysics ribbon, choose Seismic resp. in Rock Physics. Alternatively, run Fluid substitution and click Seismic response.... That route loads the selected well's Original and calculated scenarios without saving their curves first; the wizard reports their origin.
Inputs and time-depth
On Inputs, select a Well. Each log set has a Name, Vp, Vs, and Density. Use Add log set or Remove to manage comparisons. The first set is the Original, used for differences and the background trend. Up to nine sets are supported, including the Original.
Use Add saved Fluid substitution scenarios to find scenario curves already saved on the selected well. Save Vp, Vs, and Density for each scenario before using this route.
For Time-depth, choose Use checkshot and select a checkshot, or Create from Vp to build time-depth from the Original set's velocity. For the latter, set Time at the top of the log using replacement velocity from the seismic datum, a marker's seismic TWT, or a checkshot. After a successful run, Save as checkshot... stores the generated time-depth as a new named checkshot for use in other tools.
Time shift from each set's velocity is on by default: each set uses its own velocity for timing, so a slower scenario can delay events below it. Turn it off to align sets to the Original's times and compare amplitude changes alone.
Choose the depth, marker, or zone interval. For Blocking, choose None, Backus, by zone, or Backus, by thickness; enter the block thickness for the last option.
Wavelet and modelling
On Wavelet, choose a project wavelet from Wavelet Analysis or a Ricker wavelet. Set frequency and sample interval for Ricker, and adjust phase rotation while checking the preview. Project wavelets retain their own sample interval. Wavelets are normalized to a peak of 1. Polarity offers Normal (AI increase = peak) and Reverse (AI increase = trough); polarity changes the display only.
On Modelling, choose Zoeppritz (exact) (default), Aki-Richards, or Shuey, 2-term. Set the angle range and step; defaults are 0–40° in 5° steps. Set the Near, Mid, and Far angle ranges and the Intercept-gradient fit range.
Choose Top and Base markers under Events to analyse. Each event is picked as the strongest near-trace peak or trough within 5 ms of its marker time. Set Class II boundary, |A| to control the intercept threshold for classification. AVO curves and intercept–gradient analysis require event markers.
Run and compare
Click Run and check the Run report for missing inputs, gaps, or other modelling warnings. Use the log-set switches above the results to show or hide sets across views, and move the cursor over results for a readout.
- Synthetics — compare sets on a time axis. Choose the Near, Mid, Far, or Full stack, adjust Gain, and enable Difference from Original to compare changes.
- AVO gathers — compare angle gathers for the log sets, with the top and base events marked.
- AVO curves — compare event amplitude against angle. The table lists each set and event's TWT, intercept, gradient, class, Near, Far, Far / Near, and Critical information.
- Intercept–Gradient — compare samples between the events and the event points against the Original's background trend and AVO class regions.
Save results or a workflow task
Run previews results. Save stores each set's Near, Mid, and Far synthetics as depth curves and its angle gather as an array channel in a new LAS file on the well; the AVO table is stored under Statistics / Tables. For example, a synthetic is named Synthetic Near - <set>. Changing modelling inputs clears the result; run again before saving.
Save to workflow stores the setup as a Seismic response task. Running that task models again and saves results, replacing those from its previous run. A task cannot use unsaved Fluid substitution scenario curves: save them in Fluid substitution, then add them with Add saved Fluid substitution scenarios first. When editing an existing task, Run previews, Save updates the task setup, and Cancel closes without saving the edits.
Model scope
The model assumes flat layers and plane waves, uses the same angle at every interface, and includes primary reflections only. It applies no attenuation or tuning correction. Treat AVO class boundaries as interpretation conventions and check warnings before interpreting a comparison.
See Also