Rock physics

Petrophysical-to-elastic modelling — fluid and mineral mixing, dry-frame models and Gassmann fluid substitution — the bridge from well logs to seismic inversion and AVO.

Thermal and pressure state

• Temperature gradient — geotherm from surface temperature and gradient.
• Hydrostatic pressure — depth-dependent pressure for fluid-property evaluation.

Fluid properties

• Batzle & Wang — density and bulk modulus of brine, oil and gas vs. pressure and temperature.
• Fluid mixing — Reuss, Voigt, Brie and Wood averages for mixed saturation.

Mineral matrix

• Mineral mixing — Reuss, Voigt and Hill averages.
• Hashin-Shtrikman bounds — upper / lower elastic bounds.
• Cemented-sand models for the dry frame.

Rock-physics models and calibration

• Rock-physics model library for the dry-rock elastic moduli.
• Xu-White calibration by Vp/Vs to tie the model to measured velocities.
• Elastic conversions between moduli, velocities and impedances.

Fluid substitution

• Gassmann fluid substitution — recompute velocities under a changed saturation.
• Sonic porosity — Wyllie and Raymer-Hunter-Gardner relations.

This page summarises the Rock-physics section of the Wellbore.AI / Gamma technical manual.

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