TABLE OF CONTENTS So far, we have treated rocks as if they were homogeneous, solid materials. However, rocks are generally composite materials, and hence inhomogeneous on a microscopic scale. The way rocks behave, their elastic response, their failure stresses etc., depend, to a large extent, on the non-solid part of the materials. In this section we will take into account the void space, which not only is essential for oil to be produced from a reservoir, but also plays an important role in rock mechanical behaviour. We will first consider a macroscopic description of porous and permeable media, which allows us to study both static and dynamic mechanical properties. This approach is based on the theory of Maurice A. Biot.
In this section we will give a brief and practical introduction the theory. We will limit ourselves to a description of an idealized porous material which is microscopically homogeneous and isotropic. This approximation is sometimes referred to as the Gassmann limit of the Biot theory.
For those desiring a more thorough exposition, we refer to the book by Wang (2000),the papers by Detournay and Cheng (1993), Rice and Cleary (1976) and the book by Coussy (2004). Zimmerman s (1991) book is also a very useful introduction to the mechanical properties of porous media.
Let us first take a look at a very simple porous medium; namely one in which the solid and fluid parts are deformed independently of each other. In practice, we...
