Porosity Within Each Facies

The Facies Scaffold

The facies model built last chapter is the scaffold for the properties. Porosity is not modeled as one field across the reservoir but separately inside each facies, each with its own mean, spread, and variogram, then assembled. The sand cells draw from the sand porosity distribution, the shale cells from the shale one.

Honoring the Boundaries

The payoff is that porosity respects the facies: it jumps at the boundaries instead of smearing across them, high in the sand and low in the shale, with realistic variation within each. A single field that ignored facies would blur a porous sand into an adjacent tight shale, inventing rock that is not there, the same bimodal trap from the start of the facies chapter.

The Same Recipe for Everything

This per-facies recipe is general. Permeability, water saturation, and any other property are modeled the same way, each within its facies, often with the properties linked (porosity first, then permeability from porosity). Build the facies, then drape the properties on them, facies by facies.