Measuring Formation Anisotropy Using Multifrequency Processing of Transverse Induction Measurements

Abstract

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.

Biaxial Anisotropy: Its Occurrence and Measurement With Multicomponent Induction Tools

“…This leads to a concentration of electric charges in the formation volume (Tabarovsky et al, 2001). As a result, the currents, being planar and circular in the isotropic formation, follow a 3D flow pattern in the case of anisotropic medium.…”

“…MFF allows us to reduce environmental effects and simplify the data dependence on the formation parameters. MFF processing is based on an expansion of the measured field into a frequency series (Tabarovsky and Rabinovich, 1998;Tabarovsky et al, 2001). One of the series terms does not depend on the borehole and invasion properties.…”

“…12) is full. The situation becomes different when a multi-frequency focusing is applied to the magnetic matrix to extract terms proportional to ω 3/2 (Tabarovsky and Rabinovich, 1998;Tabarovsky et al, 2001). In a deviated well (non-zero relative dip), the matrix of MFF components looks similar to the magnetic matrix:…”

A New Technology for Resistivity Anisotropy Evaluation in Conductive Borehole Environments

“…In this inversion, neither a borehole nor invasion are used as integral parts of the formation models. 2,3 This model simplification may lead to a very inaccurate formation anisotropy determination. In the next section, we demonstrate that in the presence of a highly conductive borehole and invasion, both the SF and DF logs may depart significantly from those recorded in the same formation, but in the absence of both the borehole and invasion (horizontally layered, 1-D formation).…”

“…Application of HDIL data would be done primarily to derive the formation layering and the horizontal resistivity at an initial step of the interpretation process. [1][2][3] Normally, wells drilled with non-conductive oil-based mud (OBM) provide an ideal environment for induction logging tools, such as HDIL and 3DEX. At the same time, the drilling industry is turning from the use of OBM to environmentally sensitive water-based mud (WBM) systems.…”