Hydrogeological and geotechnical rock property characterization from geophysics

Boreholes drilled at Sellafield penetrated a variety of rock units. Core sa mples and wireline logs indicate that rock mass properties and in situ flui d properties vary from one unit to another, but that properties are relativ ely uniform for each unit within a particular borehole. Variability is supe rimposed upon the bulk rock mass properties, however, where faults or zones of fractured rock intersect a borehole. Furthermore, lateral variability w ithin a particular unit may be expected between boreholes and through out t he rock volume. The primary objectives of the work were: to establish a means of determinin g the spatial heterogeneity and distribution of rock mass and fluid propert ies using measurements made on core samples and derived from wireline logs; to determine the spatial heterogeneity and distribution of rock mass prope rties away from boreholes and in three-dimensions, by extrapolating the det ailed understanding gained from boreholes into the seismic survey volume; a nd to develop a visualization model of rock mass properties in three-dimens ions. It has been demonstrated that acoustic impedance is the principal property in common between surface seismic and borehole measurements, and that it pr ovides a link between the various scales of measurement. Dynamic rock quali ty and hydrogeological indices have been developed which allow qualitative comparisons to be made between the boreholes. Empirical relationships have also been established between acoustic impedance and rock quality, and betw een acoustic impedance and hydrogeological properties. These relationships enable continuous profile quantitative estimations of Rock Mass Rating and hydraulic conductivity to be made from wireline logs, and have allowed thes e properties to be extrapolated into the seismic acoustic impedance volume, thereby providing three-dimensional visualizations of the spatial heteroge neity of rock mass properties.