A more detailed understanding of the various sedimentary and directional parameters that control both porosity and permeability in sandstone reservoirs is essential in order to predict reservoir behavior. Thirteen separate sedimentary or directional measurements were made on 1,125 cores collected from outcrops of the Woodbine and Paluxy Formations of North Texas. The various sandstone bodies are of shallow marine origin, and represent marine blanket sands that may be preserved as reservoir rocks.
Grid systems were superimposed on large outcrops and random samples were collected and used to duplicate statistically reservoir characteristics. Vertical control sections within or near the outcrops were sampled and used to represent individual wells within the reservoir.
Total variability of all measured sedimentary parameters within a sedimentary unit in both random and vertical sections is very small. From a prediction viewpoint, one vertical section can be used to establish a satisfactory model for a random section within a sedimentary unit.
Permeability in these sandstones decreases as the mean grain size becomes smaller, as the sediment becomes more poorly sorted, and as the secondary cement in the rock increases. Porosity decreases as the percent cement increases. If preferred directional properties exist, permeability should increase along the preferred orientation direction and decrease in the direction normal to it.