Rock Property Calibration

Rock Property Calibration Comprises Two Main Steps:

1. Rock physics and acoustic relations analysis

   Rock physical information is taken from wells in the form of petrophysical logs (porosity, water saturation, volume of shale, and others), pressure curves, and crossplotting against the corresponding well acoustic and elastic logs (e.g., velocity, compressional impedance, shear impedance, and Poisson's ratio). Interactive tools enable detailed interrogation and analysis of acoustic rock property relationships over multiple wells and multiple intervals. The most applicable relationshipt can be selected for a particular seismic 3D volume. An additional, important part of this process is blind well testing to qualify the ability to predict properties away from the borehole.

2. Application to seismic absolute inversion attributes

   Derived relationships are applied to seismic absolute inversion attributes and velocity cubes. Seismically derived pressure, porosity, lithology, or fluid cubes are visualized, interpreted, and updated through an iterative cycle of crossplotting and well-tie analysis.

The key principles of rock property calibration are

• assessing primary physical relationships
• understanding lithology, porosity, fluid, and pore pressure distribution
• testing suitability of transforms throughout volume.

This approach has been used very successfully worldwide in many different geological environments. For example, significant success has been seen in the capability to predict effective primary porosity in back-reef carbonate shoals in Texas. Quantitative porosity has also been a key deliverable using this methodology in Jurassic carbonates offshore Mexico. Lithology and porosity in elastic reservoirs have also been accurately predicted in a number of North Sea fields.

Rock property calibration has widespread applications for rapid analysis and interpretation. It provides an effective mechanism for calibrating seismic inversion attributes to rock properties where there is sufficient well control and where relationships between acoustic and rock properties are reliable and spatially stable. This particularly applies to monomineralic rocks in quantifying seismically effective porosity in carbonates and pore pressure predictions where dependable seismic velocities are calibrated to borehole-derived pressure data.