Modeling and Inversion Methods for the Interpretation of Resistivity Logging Tool Response

The electrical resistivity measured by well logging tools is one of the most important rock parameters for indicating the amount of hydrocarbons present in a reservoir. The main interpretation challenge is to invert the measured data, solving for the true resistivity values in each zone of a reservoir. Inversion is not always an easy task because logging tools measure a bulk average resistivity. Thus reservoir heterogeneity can have a considerable effect on inversion accuracy. Two of the most significant problems are effects caused by regions adjacent to zones of interest and resistivity anisotropy (variation of resistivity with direction). The growing use of directional drilling has recently focused attention on the magnitude of anisotropy effect. Therefore this thesis concentrates on the new area of inversion in anisotropic reservoirs. The geologic origins of anisotropy are examined, and a parametric inversion method is introduced for obtaining directional resistivity values in layered media. Background is also provided on practical modeling methods for use in inversion, and on the physics of various resistivity loggingtools.