The Rock Physics section in IP
TM contains the following independent modules:
- Shear Sonic QC/Create
- Density Estimation
- Fluid Substitution
- Laminated Fluid Substitution
- Elastic Impedance
The Shear Sonic QC / Create module uses the empirical Greenberg-Castagna (1992) relationships for different minerals to calculate a synthetic shear sonic from a compressional sonic log.
When there is no density log the Density Estimation module is used to estimate it from the compressional sonic log using ‘Gardner’, ‘Bellotti et al’ or ‘Lindseth’.
The Fluid Substitution module removes the effect of the drilling fluid from the sonic and density logs and restores the log responses to those resulting from the original reservoir fluids at their original saturations.
Fluid density, bulk modulus and velocity can either be directly entered if known or calculated from Batzle and Wang (1992) in 'Seismic Properties of Pore Fluids'. Similarly, the mineral properties can be entered or selected from a menu of minerals.
The data are inverted using Gassmann's equation on a 'zonal' basis to QC the fluid and matrix properties with respect to the input velocities and parameters.
Discriminators can be applied to allow for functions to be generated for specific data, e.g. for a particular porosity range or litho-type.
The elastic parameters for two-phase fluid mixtures are calculated using a saturation curve and the fluid mixing approach of Brie et al (1995) "Shear Sonic interpretation in Gas-bearing Sands" SPE 30595 (pp701 - 710).
Once the user is satisfied that the input parameters are suitable fluid substitution is performed on the data at the well step increment. Along with the fluid-substituted density and sonic curves, both fluid-substituted Acoustic Impedance and Poissons Ratio curves are calculated and velocity and sonic slowness curves are output.
As with most modules in IPTM, up to six discriminators can be applied to allow the user to constrain the model.
In the Laminated Fluid Substitution module the user selects one of two models depending on the shale distribution. If the shale is evenly distributed (the “shaley sand” model) the bulk modulus of the solid fraction is modeled as a weighted average of the moduli of all the components of the rock. In laminated reservoirs, fluid effects only occur within the sandy laminations, and the appropriate moduli and porosity are those of the sandy laminations.
The Elastic Impedance (EI) module uses the high angle inversion equation by P. Connolly in 'The Leading Edge' (1999) and outputs EI at up to three user selected angles.