Improved processing for oil well cement evaluation-a with theoretical and laboratory data

A processing technique to measure cement impedance from ultrasonic pulse-echo waveforms, called normalized single mode (NSM) processing, is described. The technique is based on a physical model that represents the transducer in terms of its continuous plane wave kernel. Narrowband filtering to process a single resonant mode and all processing parameters are normalized to the modal frequency. The performance of NSM and a digital simulation of the present analog commercial processing, W2/W1, is compared for several environmental effects: casing thickness, eccentering, and added Gaussian noise. The computation is based on waveforms from a mathematical model and laboratory data. Results on model data show that NSM processing significantly reduces the impedance errors due to thickness variations, eccentering, and noise. Results on laboratory data indicate that the techniques yield comparable results for smooth machined casings, but that NSM processing significantly reduces measurement error and variance in a sample of the actual oil field casing.<
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