Experimental Investigation of the Effect of Pressure and Fluid Saturation on Carbonate Rocks Gary Mavko, Department of Geophysics, Stanford University, Stanford, CA 94305-2215 Carbonate rocks contain 60% of the world’s hydrocarbons. Yet, the basic understanding of how geophysical properties are related to reservoir and fluid properties is lacking, owing in part to complexities of carbonate microtexture, mineralogy, pore shape, and chemical reactivity. Through a comprehensive laboratory study, we are better defining the fundamental relationships between seismic wave propagation in carbonate rocks and the underlying porosity, permeability, pore type, and fluid content. Ultrasonic velocities in calcitic rocks (FP, GR) vary continuously with porosity, out to porosities > 50%; dolomite-bearing rocks (MSA) are faster, with shallower trend; micrite-rich rocks (MA) show a steeper slope and narrower porosity range. At the same time, micrite can drastically reduce permeability. Mineral-fluid chemical reactions modify the rock frame, yielding elastic moduli inconsistent with conventional models.