Chapter 7 - Acoustic Saturation

Abstract

The chapter reviews the pore fluid effects on acoustic velocities and attenuation. Fluid influence on the acoustic response is explained in context with Gassmann's equation, Biot's theory, and Squirt-flow mechanism. The chapter discusses the fluid substitution modeling for homogeneous isotropic rock and elaborates on the impact of pore geometry on fluid substitution. Special cases of laminated rock, dual porosity rock, and carbonates are considered for substitution modeling. More advanced cases of fluid substitution in anisotropic VTI and HTI medium is considered separately through anisotropic Gassmann's formulation, Brown-Korringa equation, Mavko-Bandyopadhyay model, and Gurevich equations. The chapter includes the discussion on partial/patchy saturations which have special sonic imprints. Key mathematical modeling is included here, and the concepts of Gassmann-Hill and Gassmann-Wood bounds are explained in context with patchy saturations. The discussion also includes various fluid mixing laws for effective fluid modulus. The chapter takes up the sonic application of saturation determination through modulus decomposition in well logs. Concepts for the clean formation and composite rock are presented and applied to shaly sand and composite carbonate with necessary theory and field examples.