TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMulti-frequency processing of transverse induction measurements (3D Explorer -3DEX™) allows us to reduce the distortion of interpretation by near-borehole effects. Recently, we have developed a multi-frequency processing technique for determining formation anisotropy in vertical and deviated wells. The method, based on a separation of induction and galvanic modes, provides a fast and stable indicator of anisotropy in real time.We consider a borehole oriented along the Z-axis. Axes X and Y are positioned in a perpendicular plane. The set of measurements under consideration includes XX, YY, and ZZ data. The magnetic field XX is excited by an X-oriented transmitter and measured by an X-oriented receiver. Similar definitions are true for YY and ZZ components.We start processing by performing a multi-frequency skineffect correction on the measured XX, YY, and ZZ data. Correction pre-conditions the data for rotation from the tool coordinate system to the formation coordinate system. As a result of the rotation, we calculate responses XX', YY', and ZZ' where axis Z' is orthogonal to the formation boundaries. Axes X' and Y' belong to the boundary planes. The rotation of multi-frequency processed data does not require knowledge of the full tensor of electromagnetic measurements: the rotation can be done only with the principle components XX, YY, and ZZ.Rotation isolates the induction mode in the ZZ component and removes the dependence on the vertical conductivity. This allows for applying a very fast processing technique to calculate horizontal resistivity of the formation, R h . The technique utilizes a modified geometric factor with the transmitter and receiver shifted horizontally with respect to each other.Next, we produce a synthetic response for XX' and YY' components in an isotropic model with formation resistivity, R h . The calculated synthetic response is used to correct the field data for the horizontal conductivity. If the formation is isotropic, the corrected signal will be equal to zero. A nonzero residual signal indicates the presence of anisotropy.The methodology is illustrated with several examples.