HYDROGEOPHYSICAL PROPERTIES OF PARTS OF THE BRITISH TRIAS*

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Abstract
Laboratory studies of Bunter Sandstone specimens from Northwest Lancashire, Shropshire, West Cumberland, and the Vale of Clwyd have indicated that the parameters effective porosity, intergranular permeability, compressional wave velocity, formation resistivity factor, and effective matrix resistivity have significantly different distributions in each of these four regions. Regression analyses have shown that bivariate and trivariate expressions for the prediction of the two hydrological parameters from petrophysical data vary from region to region. It is concluded that, in quantitative geophysical investigations of these formations, each area must be investigated independently.For all four aquifers, and for both horizontally and vertically oriented specimens, effective porosity can be most reliably and readily estimated through a bivariate relationship involving formation resistivity factor. On the other hand, the best estimate of intergranular permeability from geophysical data is obtained through a trivariate expression involving both formation resistivity factor and effective matrix resistivity. The use of hydrogeophysical relationships to estimate hydrological parameters in situ is illustrated by reference to field examples.