Fluid effects on seismic waves in hard rocks with fractures and in soft granular media

When fractures in otherwise hard rocks are filled with fluids (oil, gas, water, CO{sub 2}), the type and physical state of the fluid (liquid or gas) can make a large difference in the wave speeds and attenuation properties of seismic waves. The present work summarizes methods of deconstructing theses effects of fractures, together with any fluids contained within them, on wave propagation as observed in reflection seismic data. Additional studies of waves in fluid-saturated granular media show that the behavior can be quite different from that for fractured media, since these materials are typically much softer mechanically than are the fractured rocks (i.e., having a very small drained moduli). Important fluid effects in such media are often governed as much by fluid viscosity as by fluid bulk modulus.