Porous and cracked rocks elasticity: Macroscopic poroelasticity and effective media theory

Macroscopic poroelasticity and effective medium theory are two independent approaches which can be used to analyze the role of pores, cracks, and fluid on elastic properties. Macroscopic poroelasticity belongs to the macroscopic framework of thermodynamics whereas effective medium theory expresses the medium properties in terms of microstructural characteristics (pore and crack shape, etc.) and component properties (fluid properties, solid grain properties, etc.). In this paper, we review the fundamental assumptions and results of both approaches, and show that they are complementary but do not apply over the same range of conditions. A compilation of data is reported, in various dry and saturated rocks, to show the validity of the Gassmann equation and the dispersion between unrelaxed modulus -where effective medium model applies- and relaxed modulus -where poroelasticity applies.