Seismic Waves Propagation in Porous Media: A Pore-Scale Study

Natural geomaterials and sediments contain a complex pore structure, with the skeletal portion of the material called the “matrix”. The soil as a porous medium itself can be assumed as a three-phase system that consists of a solid phase (soils), a gaseous phase (air), and a liquid phase (groundwater). The engineering properties of geomaterials are directly linked to the composition of matrix including the pore space structure and saturation. The transmission of seismic waves through these complex systems has been always an important research subject as the propagation of shear and compressional waves (S- and P-waves) can be used to explore the characterization of geomaterials in subsurface.

In this study, we study the seismic waves propagation in porous media through a pore-scale study. The goal of this work is to discover relationships between pore-scale characteristics media (distribution, heterogeneity and saturation) and seismic wave propagation in porous media. Random two-dimensional porous media are generated with different porosity (0 to 0.5), pore space heterogeneity (from uniform to highly heterogenous), and saturation (dried to fully water saturated). The models are imported into the Finite Element Method software package, COMSOL Multiphysics to simulate the propagation of seismic waves. A step pulse is transmitted on one boundary while the response is monitored via a probe on the other opposite side of the model geometry. The waves are propagated in both longitudinal, and horizontal directions to simulate pressure and shear waves. The Impacts of pore-scale characteristics of soils on shear- and pressure-wave travel times are determined and finally, a signal analysis methodology is suggested to identify both S-, and P-waves travel times in a complex porous medium by comparing the wave behavior with a non-porous medium.