Application of Geophysical and Spectral Methods in Non-invasive Characterization of Porous Media : A Critical Review

Abstract

The objective of this research is to use geophysical methods and spectral analysis techniques for non-invasive characterization of the subsurface in cold regions under isothermal conditions. As a component of the research, this paper provides a critical review of the various geophysical techniques used for characterization with special mention of the application of spectral methods and discussion on the choice of suitable surrogates. Traditional methods of porous media characterization such as pumping tests are invasive and unsuitable for many reasons including the high-cost involved, inability for local scale characterization, and possible contamination problems due to alteration of flow regime. Attempts for non-destructive characterization of subsurface hydraulic properties have resulted in the development of many conceptual and theoretical models. Attributes of the porous media such as porosity, grain size, packing, and geological texture and structure, are known to have direct control on permeability and may be used as surrogates for its estimation. Since complete three-dimensional information of the subsurface is very difficult to obtain, two-dimensional maps of the surrogates aided by heuristic knowledge of the geologic controls on hydraulic properties may be useful for characterization. Most of the non-invasive characterization methods have utilized correlation of such inexpensive, measurable surrogate(s) with permeability in conjunction with one or more geophysical methods (e.g. GPR). Success of such methods depends largely on the choice of suitable surrogate(s) and strength of their correlation with the target property (viz. permeability). Researchers have used spectral analysis techniques to enhance and extrapolate signatures from the images or maps of the surrogates to study possible correlation with permeability for continuous mapping of the permeability.