Inversion-based workflow for oilfield nested multicasing evaluation using electromagnetic low-frequency measurements

An inversion-based interpretation workflow is developed to determine individual thicknesses of multiple nested casings using induction-based multispacing and multifrequency measurements. It includes an inversion-based channel calibration to determine unknown casing permeabilities and conductivities while the presence of casing eccentering is indicated by a QC flag. The inversion-derived data covariance matrix provides the uncertainty estimates in the inverted casing thicknesses. The derived data resolution matrix reveals the measurement information content which has helped in optimizing the importance of each channel in multifrequency data and in defining measurement accuracy for required casing thickness resolution. The proposed workflow is capable of handling an arbitrary number of nested casings and has been validated on synthetic and field data sets.An inversion-based interpretation workflow is developed to determine individual thicknesses of multiple nested casings using induction-based multispacing and multifrequency measurements. It includes an inversion-based channel calibration to determine unknown casing permeabilities and conductivities while the presence of casing eccentering is indicated by a QC flag. The inversion-derived data covariance matrix provides the uncertainty estimates in the inverted casing thicknesses. The derived data resolution matrix reveals the measurement information content which has helped in optimizing the importance of each channel in multifrequency data and in defining measurement accuracy for required casing thickness resolution. The proposed workflow is capable of handling an arbitrary number of nested casings and has been validated on synthetic and field data sets.