Abstract

A numerical procedure for predicting cavity signatures for a dipole-dipole array configuration in hole-to-hole resistivity measurements has been developed. This electrode geometry is implemented from the general solution for a point source of current near an air-filled cylindrical cavity or an air-filled cylinder surrounded by a concentric conductive or resistive halo region embedded in a homogeneous conducting host medium to simulate hole-to-hole resistivity measurements. Cavity signatures obtained for several vertical offset distances between the source and detector dipoles as well as multiply spaced dipole-dipole responses suggest that a processing technique may be devised to identify directly the position of the cavity inhomogeneity with respect to the boreholes. The results also show that the presence of a concentric halo region more conductive than the host medium influences the overall signature by either reducing or enhancing the effect of the air-filled cavity depending upon the halo size and conductivity contrast. In comparison, a halo region more resistive than the host medium always influences the composite signature by enhancing the effect of the air-filled cavity.

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