OVERVIEW

The nature of reservoir rocks containing oil and gas dictates the quantities of fluids trapped within the void space of these rocks, the ability of these fluids to flow through the rocks, and other related physical properties. The measure of the void space is defined as the porosity of the rock, and the measure of the ability of the rock to transmit fluids is called the permeability. A knowledge of these two properties is essential before questions concerning types of fluids, amount of fluids, rates of fluid flow, and fluid recovery estimates can be answered. Methods for measuring porosity and permeability have comprised much of the technical literature of the oil industry. Other reservoir properties of importance include the texture, the resistivity of the rock and its contained fluids to electrical current, the water content as a function of capillary pressure, and the tortuous nature of the interstices or pore channels.

The texture of sedimentary rocks is determined largely by grain shape and roundness, grain size and sorting, grain orientation and packing, and chemical composition. A specific combination of these variables may reveal information about diagenetic and catagenetic processes and mechanisms operating during transportation, deposition, and compaction and deformation of sedimentary materials. In some cases, texture may yield some information about formation permeability and porosity. For example, fine-grained sandstones with poorly sorted angular grains will generally have lower porosity than sandstones composed of coarse, well-sorted grains. Variation in permeability may be predicted from variation in grain size and shape,...