Abstract

The formation factor (ratio of bulk resistivity of rock to resistivity of formation fluid) obtained from the focused-electrode log can be used to estimate the hydraulic conductivity of the unfractured granitic rock matrix (10 (super -12) -10 (super -10) m/s), using an empirical relationship developed between laboratory measurements of formation factor and permeability. The ratio of the formation factor derived from the focused-electrode log (F F ) to the formation factor derived from the density log (F B ) may be used to estimate the hydraulic conductivity of fractured zones (10 (super -9) -10 (super -6) m/s), because of the following empirical relationship between the transmissivity (T H ) obtained from the in-situ hydrogeologic tests and the ratio of the two formation factors, namely,Equationwhere A and s are coefficients (4.1 X 10 (super -7) and 1.06).This empirical relationship confirms the usefulness of geophysical logs for identifying intervals of potentially high permeability in boreholes drilled in granitic rock. Estimates of hydraulic conductivity derived using these relationships can help obtain a qualitative understanding of hydrological conditions in a crystalline rock mass.

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