Reservoir Properties of Conglomerates and Conglomeratic Sandstones: GEOLOGIC NOTES

Bimodal clastic sedimentary rocks can be either “sand packed,” where pebbles are dispersed through a continuous sandstone matrix, or “pebble packed,” where sandstone partially or wholly fills the interstices between a framework of densely packed pebbles. The primary porosity of bimodal reservoir rocks may vary by a factor of 3 to 4, depending on the packing state and the relative proportions of sand and pebble-sized grains in the rock. The relations between permeability and porosity, and water saturation and porosity, in bimodal reservoir rocks may be quite different from those common in clastic reservoirs having unimodal grain-size distributions. The effects of bimodality and diagenesis should be considered separately for a better understanding of the properties of bimodal reservoir rocks.