Figure 25. SEM micrographs with porosity and permeability data that illustrate the general petrographic and reservoir characteristics of sandstone chromatic zones. A. White zones (highest resistivity) are cemented and have low porosity. B. Yellow zones (intermediate resistivity) show high porosity and permeability. C. Orange zones (lowest resistivity) are characterized by high porosity but low permeability as the result of abundant pore-filling authigenic clays.