Constrained Simultaneous Inversion (Absolute)

Description Inverts for absolute P-Impedance, S-Impedance and Density from seismic stacks.
Module(s) Rock, Lithofluids
Requirements Volume
Related Constrained Simultaneous Inversion (Relative), Windowing models, LF model (Ghost Horizon Inverse Distance), LF model (End member Trends), LF Model (Simple Kriging)
Works with Stacks, 2D

This process inverts for absolute P-Impedance, S-Impedance and Density from seismic stacks. One stack is required to invert for P-Impedance, two stacks are required to invert for S-Impedance and three or more stacks are required to invert for Density.

  1. In the Control Panel, open the Process tab.
  2. At the tab header, click the Add icon and select New Process.
  3. Scroll down and double-click on Constrained Simultaneous Inversion (Absolute).
  4. Type a name for the process and click OK.

Note: Stacks should be frequency balanced. If not, impedance volumes may have different energy spectra. Wavelet spectra should match the highest signal to noise window of the seismic spectra.

Configuring Constrained Simultaneous Inversion (Absolute)

Smooth a 2D/3D volume
  1. Blue (+): add a stack detail row.
  2. Traffic light: include (green) or exclude (yellow) a stack from the inversion
  3. Name: Enter a label for each stack. Default stack names are generated, e.g. Near, Mid, Far, Ufar, etc.
  4. Angle: The average stacking angle
  5. Wavelet: Select a wavelet
  6. Seismic: Select the stack volume
    • For 2D inversion, all stack volumes must be 2D
    • For 3D inversion, all stack volumes must be 3D
  7. Weight: The stack weight (default 100). Stack weights affect the influence of each stack on the inverted result
    • e.g. Lower the weight of a noisy stack to reduce its influence.
  8. Red (x): Remove that row

Low Frequency Models

Select a 3D low-frequency model volume for:

  1. P-Impedance
  2. S-Impedance
    • Only available for two or more stacks
  3. Density:
    • Only available for three or more stacks

Time-Depth

  1. Velocity: Select the velocity model to use for time-depth conversion. It is required for all inputs in depth, e.g.
    • Stacks
    • Low frequency models
    • Horizons
    • Rock-physics trends (always required)
  2. Water bottom: select a horizon or enter a constant
    • The water bottom is only required when using rock-physics trends.

Inversion Parameters

Frequency

  1. Notch (Hz): the frequency dividing the contribution from the low-frequency model and the seismic.
    • The notch frequency is usually set at the lowest frequency of the seismic with good S/NR.
  2. Top End (Hz): the highest frequency (from the wavelets and seismic) with good S/NR
    • Frequencies above the top-end value are damped and contribute less to the inversion result

Weights

Use weights to influence how much each set of parameters contribute to the inversion result. The inversion solution takes all constraints into account with their associated weights. Most parameters are relative weights for each constraint, but they are not percentages.

The default for most weights is 100. Every dataset is different, so test different weights to determine their influence, e.g. low (50), default (100), high (200) and extreme (1000).

  • Seismic Match: the match between post-inversion synthetics and the input seismic.
  • LFM Match: the match between post-inversion low frequency and the input LF models (below the notch frequency).
  • HF Damper: how much damping is applied to frequencies above the Top End.
  • Physical Bounds: how strictly to apply the physical property constraints.
  • AI-SI Variance: (default 0) increase the similarity between AI and SI variance.
  • AI-SI Correlation: (default 0) increase the correlation between AI and SI.
  • AI-Rho Variance: (default 0) increase the similarity between AI and density variance.
  • AI-Rho Correlation: (default 0) increase the correlation between AI and density.

Variance and correlation to P-Impedance should be driven by the seismic (default 0). Try other values to stabilise results.

Physical Properties

The inversion solution is driven by the seismic and other constraints. Physical property bounds bias the solution away from values that fall outside the boundaries. Property bounds are not hard limits.

  • Physical property bounds are disabled by default.
  • Enable the checkbox to apply a property bound.
  • Enter the minimum and maximum property value.

Rock Physics

The AVA covariance constraint ensures that the covariance of the inverted AVA coefficients (intercept, gradient, and curvature reflectivity) and associated background trend are consistent with expected rock physics relationships and are not biased by noise.

  • Trend Set: Select a trend set (load in the QI tab).
  • Lithology: Select the lithology with the expected background covariance.
  • Weight: The influence of the covariance constraint on the solution.

Output

Calculating the inversion can be slow. Save time by using output constraints (Window and Area) to limit the results to the target interval.

Window

Specify the vertical output extent of the inversion solution using constant values or horizons.

  • Start: the top of the window
  • Stop: the end of the window

Area

  • Limit to area: Limit the calculation spatially to a polygon or probe

3D Extents

  • Set the inline, crossline and time extents for the output.

Note: Inline/Crossline extents are disabled when used as a workflow process.

2D Extents

Set the time extent for the output (applied for all lines).

  1. Line Set: Select a line set to limit the output to its lines.
  2. Traffic light: Enable or disable all lines.
  3. Set Spacing: Enable increment setting for each line, both in distance and CMP spacing.
  4. For each line:
    • Traffic light: Enable or disable this line.
    • CMP Range: The first and last CMP to output, and the step size.

Naming

  • Prefix: If provided, use this prefix for output volumes, instead of the process name

Volumes

Many output volumes can be generated by the process. The results are grouped by type.

  • Enable or disable a checkbox to include these outputs in the results.

Output Groups

Absolute (default)

  • P Impedance
  • S Impedance
  • Vp/Vs
  • Density

Relative

  • P Impedance relative
  • S Impedance relative
  • G Impedance
  • C Impedance

Relative (scaled)

  • P Impedance relative scaled
  • S Impedance relative scaled
  • Density relative scaled
  • Vp/Vs relative scaled

AVA

  • avo0
  • avo1
  • avo2

Synthetic

  • Synthetic ...
    • One synthetic volume is created for each input stack
  • Residual ...
    • One residual volume is created for each input stack

Reflectivity

  • P reflectivity relative
  • S reflectivity relative
  • Rho reflectivity relative
  • Reflectivity ...
    • One reflectivity volume is created for each input stack

Stack Impedance

  • Impedance relative ...
    • One stack impedance volume is created for each input stack

Low Frequency

  • P Impedance LF
  • S Impedance LF
  • Density LF
  • Vp/Vs LF

Runtime log

The Runtime Log window shows the progress of the interactive calculations and error messages.

  • Suspend logging: When enabled, the log window is not updated
  • When disabled, runtime log messages will appear

Inversion Parameters

A text summary of the inversion parameters.