A Review Of Pore And Grain Geometric Models Available to Purchase

Pore and grain geometry influences the electrical conductivity, dielectric constant, permeability, and elastic moduli of oilfield rocks. The geometrical effect is of such fundamental importance that many different models of disparate types have been developed that each account for various aspects of the behaviour of rocks. Recent interest has centered on the complex dielectric function, giving rise to several methods of dielectric constant and conductivity interpretation. The abundance of these methods is encouraging, but it can also lead to confusion if their physical basis and limitations are not well understood. Geometric models are used to derive a "mixing law", so that a physical property of the composite rock can be predicted from knowledge of the properties of its constituents and their geometric arrangement. In the simplest case of two component systems the mixing parameter is often simply the porosity. As reservoir rocks contain hydrocarbons and often clays it is necessary to extend mixing laws to three or four component systems. Although some (but not all) models have been developed to this complexity, the basis of each is presented in terms of two components. We discuss three categories of geometrical models based respectively on networks, suspensions, and grain growth. In addition, we review some empirical models and the known physical bounds on the behavior of rock properties. As it is not possible to cover the literature completely, our aim is to describe the basic principles of each approach and to review its successes and limitations from the viewpoint of the log analyst who is interested in practical applications. Most emphasis has been placed on electrical properties, but a critical approach is also taken to the potential that each method has for unifying our understanding of electrical, mechanical, and fluid transport properties.