In recent years, triaxial induction logging has been successfully used for the evaluation of anisotropic reservoirs. A new triaxial induction tool has been developed to tackle the difficulties encountered evaluating conventional and anisotropic reservoirs. This new tool uses a plurality of frequencies and a combination of standard and triaxial coil arrangements to deliver the desired formation properties. It is well-known that the borehole significantly affects triaxial measurements, even in oil-based mud (OBM) environments, and these effects are much stronger for shorterspacing arrays and at higher frequencies. Consequently, the logging measurements must be corrected for borehole effects before they can be used to obtain accurate reservoir properties. This paper presents a novel borehole-effect correction (BHC) algorithm designed to correct the borehole effects of multi-component induction (MCI) data acquired in OBM wells. The proposed BHC methodology uses a modelbased multistep inversion method to determine all unknown formation parameters. After these inverted parameters are obtained, they are used in a forward model to compute the borehole effects to each array and frequency, and to apply these corrections to the calibrated logging data. The borehole corrected data is finally used as input for the ensuing inversion that provides the desired product answers. The accurate and fast inversion for the unknown parameters is the key role in this new BHC scheme. The proposed multistep inversion algorithm based on a radial 1D (R-1D) model is implemented by splitting the inversion problem of one high-dimension unknown vector into several lower-dimension ones, based on their sensitivity to different components of measured conductivity tensors for different subarrays operated at different frequencies. This reduction in dimensionality makes the BHC non-linear inversion considerably faster, more reliable, and robust. As its by-products, the BHC system also provides real-time inverted formation parameters, tool location in the borehole, and borehole size. To test the newly developed BHC method and system, MCI synthetic data and field log data have been processed for the borehole correction by using the new algorithm. The corrected results show that the BHC based on the multilevel processing and multistep inversion approach is fast, reliable, and robust, enabling it to be accurately used for real-time data processing.
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