A New Method of Detecting while Drilling Resistivity Anisotropy with Azimuthal Electromagnetic Wave Tools

With the extensive application while drilling of azimuthal electromagnetic wave tools in highly deviated wells or horizontal wells, resistivity anisotropy is currently one of the main factors influencing geosteering and formation evaluation accuracy. Different signals may interface from the azimuthal electromagnetic wave tools. The study used numerical simulation on Baker Hughes’s APR tool to determine the effect of resistivity anisotropy on the response of each component signal. In the simulation, the effect of anisotropy was enhanced or removed by using the symmetrically transmitted compensation measurement. The anisotropy of formation resistivity was calculated from forward and inversion. It showed in the simulation that when relative deviation angle was in the range of 0°-90°, axial component of magnetic field signals increased monotonically with resistivity anisotropy and both followed the parabolic law. When the relative deviation angle was 0° or 90°, the effect would diminish. The anisotropy of formation resistivity could be confirmed effectively by the combination of different signal components of electromagnetic resistivity tools while drilling. Horizontal resistivity, vertical resistivity and relative deviation angle might be obtained from three-parameter inversion on azimuthal electromagnetic wave response data. Formation evaluation and geosteering may be more accurate when based on the inverted measurement data.