Sensitivity and Limitation in Determining Resistivity Anisotropy with Different Electromagnetic Logging Measurements

Information about anisotropic resistivities is essential in evaluating the hydrocarbon in site accurately as well as making more confident geosteering decision in LWD application. Although it is easy to obtain the resistivity anisotropy using wireline multi-components induction logs, for other electromagnetic logging methods, such as: conventional LWD resistivity measurement, dual-induction logging, laterolog, or even azimuthal resistivity LWD measurements, this information is still not readily available.

Thus, questions arise when implementing these measurements in High Angle and Horizontal (HAHZ) wells where the anisotropy effects are normally non-ignorable. What are the sensitivities of these measurements to resistivity anisotropy? What are the limitations of these measurements when they are applied in anisotropic formation? Can we derive the anisotropic resistivities from these measurements individually? or additional inputs are needed?

In this paper, we present a comparative study on the sensitivities and limitations of anisotropy evaluation for all kinds of EM logging tools. Special emphasizes will give to the measurements which are not specific designed for this purpose. A “sensitivity function” and scaling factor are also introduced to make the sensitivities of different measurements comparable.