Abstract

The transmission surface or network technique was used to study the induced-polarization response of a model having infinite strike length. The model consisted of a horizontal cylinder (the target) in a uniform half-space overlain by an overburden. Responses to the dipole-dipole, pole-dipole, and gradient electrode arrays were compared as model parameters were systematically varied. Target conductivity, target depth, and overburden thickness and conductivity were each changed in turn. For different electrode spacings and locations, the peak response amplitudes and positions were plotted.It was found that the peak response amplitude did not decrease when large electrode spacings were used. The maximum percent frequency effect (PFE) response remains relatively constant for mildly conductive to very conductive targets. At the same time, the electrode separation required to achieve this maximum response increases by about a factor of two. The position of the peak PFE and the amplitude of the peak metal factor (MF) response were insensitive to overburden conductivity. There is a sharp drop of both PFE and MF when a thin overburden is introduced, and a gradual further reduction as its thickness increases. Responses to the pole-dipole and dipole-dipole arrays were comparable in magnitude, whereas results for the gradient arrays were at best equivalent and sometimes much smaller.

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