Novel ultrasonic data processing to detect ultralight cement behind casing - a field study from Utsira High in the North Sea

By evaluating the frequency spectrum of the flexural wave, a perturbation in the analyzed dataset is observed. Since this perturbation is connected to the flexural phase velocity overlapping the P-wave in the annulus, we can exploit it by picking the frequency where the perturbation occurs and use this to estimate the velocity of the annulus material. Based on this philosophy, we present a method to distinguish solids and fluids based on the estimated velocity. The outcome is a binary algorithm that either detects a perturbation or not, and in addition a method that differentiates between annulus materials using the estimated velocity.