Permeability and the Poro-Perm Transform
Learning objectives
- Explain why permeability is derived from porosity
- Describe the log-linear poro-perm transform
- Explain why the relationship is a cloud, not a line
- State why the scatter matters for flow
From Porosity to Permeability
Permeability matters most for flow yet is measured at the fewest points, so it is usually derived from the modeled porosity through a poro-perm transform. The transform is log-linear: the logarithm of permeability rises in proportion to porosity, because permeability ranges over orders of magnitude where porosity ranges over only a few percent.
A Cloud, Not a Line
The poro-perm relationship measured on core is a scatter cloud, not a clean line: at one porosity, permeability can vary tenfold, because pore geometry and not just pore volume sets flow. A good model carries that scatter, often by cosimulating permeability with porosity rather than applying a single deterministic curve.
Why the Scatter Matters
The scatter is not a nuisance to average away. The high-permeability tail, the streaks and thief zones, dominates flow and recovery, and those highs are exactly where the poro-perm scatter is largest. Carrying the scatter, and its uncertainty, is what lets the model capture the connected high-permeability pathways that decide how the reservoir produces.