In-situ Porosity and Permeability Estimation from the VSP Data Using Integrated Poroelastic Model

Reliable estimates of in-situ porosity and permeability in the water-saturated near-surface soil layers are important in diverse engineering projects. However, it is difficult to obtain these estimates, especially in loose sandy soils. In particular, the estimation of in-situ permeability is extremely difficult. Also porosity and permeability are related parameters in porous formations. An approach which can simultaneously estimate the in-situ porosity and permeability values has added scientific merits. For this purpose, we have looked at poroelastic wave propagation in the subsoil. A field database for seismic dispersion was compiled to test the applicability of various poroelastcity models to water-saturated, onshore sands and clays, in the field seismic frequency range. Using the most applicable poroelastic models, we have presented a physics-based integration approach that combines P- and S-wave velocity and attenuation. We show the existence of convexity in the parameter domain when we integrate velocity with attenuation through a cost functional. This allows for estimation of both porosity and permeability uniquely and simultaneously. The approach was tested on synthetic VSP seismograms. With realistic error in data and model, the approach still appears to give reasonably accurate values of both porosity and permeability.