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What is Pre-stack Inversion?



What is Pre-stack Inversion?

If you are looking to invert offset gathers for P-impedance, S-impedance and density then you are looking for Pre-stack inversion

Pre-stack inversion transforms seismic angle or offset data into P-impedance, S-impedance, and density through the integration of gathers, well data, and stratigraphic interpretation. Other elastic parameters such as Vp, Vs, and density are also equally possible, but typically two components such as P-impedance and Vp/Vs ratio, are reliable depending on target acquisition.

The data needed for a pre-stack inversion project typically consists of P and S wave reflectivity stacks, intercept and gradient stacks (which are converted to Rp and Rs stacks, and a minimum of 3 angle stacks (converted to Rp and Rs density stacks).

Pre-stack inversion software is available through IHS Kingdom. There are plenty of benefits of using this software to convert your seismic inversion data including:

  • An elastic log analysis to identify targets
  • Cross-plot any pairs of logs
  • AVO analysis on multiple angle stacks
  • EEI and log correlation analysis
  • Cascaded and constrained inversion for AI, SI and density
  • Wavelet estimation for P-impedance, S-impedance and density reflectivity volumes
  • Elastic parameters transform to Poisson’s ratio and Young’s modulus etc.
  • Mapping reservoir properties using polygons
  • Estimate porosity, VSH, SW and TOC using EEI and log correlation
  • Simple to set up and easy to parametrize and supports multi-CPUs
  • Suitable for both conventional and unconventional reservoirs
  • Fully integrated with Kingdom project database as there is no data transfer time

There are many features within the software including, Log Analysis, Cross Plot, EEI Correlation, Pre-stack Data Analysis, Elastic Parameter Transformation and Litho-Fluid Mapping.

Log Analysis

The log analysis tab in the software shows various elastic logs that are currently used in the industry – Vp, Vs and Density. Other petrophysical logs which are also included are gamma-ray, water saturation and total organic carbon so they can also be displayed alongside your data.

Cross Plot

With Cross Plot you can pair together elastic parameters to find a relationship between elastic and any petrophysical logs. A third log can also be selected as the colour bar which adds further detail to the plot.

EEI Correlation

EEI (Extended Elastic Impedance) is a clever way of combining intercept and gradient domain, the values of compressional velocity, shear velocity and density with a rotational angle called chi. When the angle, chi, is zero, the extended elastic impedance value is the normal incident acoustic impedance The Chi angle is used in the Log Analysis and Pre-stack Data Analysis tab.

Pre-stack Data Analysis

Once the prospect has been established using the above tools, you can then proceed to prepare data for the inversion. This module takes angle stacks and performs an AVO analysis to transform them into P, S and Density reflectivities.

Elastic Parameter Transformation

Once the 3 inversion volumes have been generated you can use this feature to transform and look at the relationships defined using real well data which can be applied to the volumes which will result in a series of elastic and petrophysical volumes that represent the desired property and trace location.

Litho-Fluid Mapping

As soon as the Elastic parameter volumes have been created this module will allow you to cross plot the two selected volumes around a well.