CONNECTING AQUIFER PROPERTIES TO BOREHOLE GEOPHYSICAL DATA: AN OVERVIEW

Geophysical logging provides a wide range of high resolution physical property measurements of aquifer materials in the vicinity of boreholes, supplementing information from coring and observation wells. Cross-borehole geophysical methods permit tomographic imaging of the region between boreholes, providing information about spatial variability within aquifer systems. These surveys can be repeated periodically to observe temporal changes due to in situ aquifer processes. However, the physical properties that affect borehole geophysical techniques (e.g., electrical resisitivity, neutron capture cross-section) are not the aquifer parameters necessary for groundwater modelling (e.g., hydraulic conductivity, specific storage). Therefore, the extraction of information about hydrogeological conditions in aquifers from borehole geophysical data requires the development of petrophysical relationships connecting these two types of properties for porous rocks and soils. Most of the present relationships are unsophisticated; hence, the use of geophysical borehole methods commonly yield only qualitative or semi-quantitative information about aquifer properties in real world applications. This presentation will review the efforts underway to improve the extraction of quantitative aquifer information from borehole geophysical data. In particular, it will examine the recent laboratory studies and theoretical modelling that is establishing the connection between geophysical properties and aquifer parameters. A major theme of this work is to link these macroscopic properties with microstructural features and phenomena occurring in porous media in an attempt to develop a unified framework for inferring aquifer properties from geophysical data.