Generating synthetic stacks from Intercept and Gradient volumes
An overview of the workflow:
- Calculate reference angle stacks from the gathers (see Angle Stacks).
- Calculate intercept and gradient from the gathers (see Intercept/Gradient).
- Use Shuey's approximation to calculate the synthetic volume (see Volume Maths).
- (optional) Band-limit the synthetic to match the reference stack (see Band-pass Filter).
- Calculate the residual using Volume Maths.
Setup
In this example, we prepared the following data:
For Angle Stacks
- Load gathers
- Load velocity model
- Draw a map polygon
- Create a window model to evaluate spectra at the target
For I/G calculation (from gathers)
- Define angle mutes
- Load gathers
- Load velocity model
Use this workflow. Repeat steps 3, 4 and 5 for additional angles.
The spectral analysis window is included as a reference.
- Yellow = Stack
- Orange = Synthetic
- Red = Filtered Synthetic
- Black = Residual
Workflow
- Create angle stacks from the gathers. We will be using the average of the min and max stacking angle for Shuey's equation.
- Calculate Intercept and Gradient from the gathers. Use angle mutes to avoid including near-offset noise and NMO stretch.
- Use Volume Maths and Shuey's equation to calculate the amplitude using the Intercept and Gradient results for a specific angle. Note that the trigonometric functions expect radians as input (e.g. for 30 degrees).
- Formula: I + G * (sin(30*pi/180)^2)
- Depending on your data, the synthetic result may contain more high-frequencies than your angle stack, increasing the energy in the residual. By applying a bandpass filter, we can match the synthetic spectrum to the stack spectrum.
- Finally, calculate the residual between the stack and the synthetic using volume maths.
