A Simple Approach to Mud-Invasion Correction for Dual Laterolog Resistivities

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ABSTRACT A simple approach to mud invasion correction for dual laterolog resistivities is proposed in this paper. This approach was derived from an idealized formation model for laterolog resistivity measurements. In this model, the measure current is assumed to flow horizontally into the formation and the invasion radius is assumed to be less than the radial depth of investigation of the shallow-laterolog. Instead of a "pseudo-geometrical factor", the tool calibration coefficient was introduced into the laterolog response equations. As a result, the correction for the mud invasion effect on the laterologs can be made without knowing the diameter of mud invasion into the formation. Once the true resistivity of the un-invaded formation is determined from the dual laterologs, the invasion diameter can be further estimated for medium- to high-porosity formations.