Preface

Rock physics is the part of geophysics concerned with establishing relations between various properties of rocks. Because the elastic radiation is the main agent that allows us to illuminate the subsurface, the primary emphasis of rock physics has been to relate the elastic properties of rock, including the P- and S-wave velocity, P- and S-wave impedance, and Poisson’s ratio to porosity, lithology, and pore fluid. A significant number of such rock physics models (transforms) have been developed based on experimental data or physical theories or both. These models enable us to forward model the elastic properties of rock as a function of porosity, rock texture (arrangement of grains or cavities at the pore-scale level), mineralogy, and the compressibility of the pore fluid. Because the seismic reflection depends on the contrast of the elastic properties in the subsurface, rock physics helps generate synthetic seismic reflections at an interface between two different rock types, such as a non-reservoir rock cap and petroleum reservoir, as well as at a fluid contact within a reservoir itself (e.g., gas/oil contact and oil/water contact).

However, in field applications, we face an inverse problem whose solution is not unique: how to interpret a seismic event, which is manifested by a reflection amplitude that stands out of the background, in terms of reservoir properties and conditions. The inherent difficulty of this problem is that the number of variables required to produce the elastic properties of porous rock is larger than the number of seismic observables. Various approaches have been developed to tackle this uncertainty; most of them based on statistical techniques that help assess the probability of the occurrence of a certain object (e.g., high-porosity sand filled with oil) at a given location in a 3D subsurface. Even when using statistical techniques, forward modeling of seismic reflections based on either well log data or theoretical rock physics is a key element of interpreting seismic data.