Computation of Triaxial Induction Logging Tools in Layered Anisotropic Dipping Formations

In order to interpret the logging data from triaxial induction tools, inversion technology has been adopted. To make the inversion process reasonably fast, a fast forward method must be developed. Numerical methods, such as the finite element method and finite difference method, are flexible but slow for inversion purposes. In this paper, an analytic method is developed to simulate induction tools in deviated wells drilled in anisotropic formations. This method can be applied to the triaxial induction tools with transmitting and receiving coils oriented in three mutually perpendicular directions. The axis of the tool may intercept a formation with dip, azimuthal, and orientation angles. Formulations of the electromagnetic fields generated by these three transmitting coils are derived. The derivation uses the coefficient propagator method with the assumption of negligible borehole effect and invasion zones. This method overcomes the problem of numerical overflow without compromising the accuracy of the solution. Because the new induction tool has three transmitting and three receiving coils, a total of nine logs are obtained at each logging depth compared with one or two logs in regular induction or logging while drilling tools.