Abstract

We describe numerical simulations of anomalous dual-laterolog (DLL) borehole measurements, including Delaware and Groningen effects. Both effects give rise to abnormally high readings of DLL measurements under extreme logging conditions. Specifically, a low resistive bed below a highly resistive layer causes electrical currents to concentrate within the borehole, which generates a negative potential at the reference electrode and, consequently, an abnormally high reading in DLL measurements. These effects are exacerbated by the presence of casing and/or at nonzero frequencies. Simulations are performed with a 2D goal-oriented, high-order, self-adaptive hp finite-element method together with an embedded postprocessing method. Results indicate that the presence of electrodes B and N is critical for proper simulation of Delaware effects on DLL measurements. Delaware effects on DLL logs decrease as the current return electrode is moved farther away from either the logging point or the borehole. The frequency of operation also affects deep laterolog measurements, generating the so-called Groningen effect.

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