Weak reflection enhancement and picking from ultrasonic pitch-catch measurements in cased-hole

Ultrasonic logging is a widely used technology to assess the cement bond condition in cased-hole. Advanced ultrasonic pitch-catch measurements can capture reflections at the cement-formation interface (or the Third-Interface-Echo, TIE in short), which enables the evaluation of the bond condition, casing eccentering, and the velocity of material in the cement annulus. However, the usage is limited by the TIE arrival picking due to the low amplitude resulting from the eccentered tool and casing, overlapping with tool-casing multiple reflections, as well as interference from the primary zero-order antisymmetric Lamb wave (A0). We develop a two-step method to enhance and accurately pick the TIE arrivals. We firstly employ the Mathematical Morphological Filtering (MMF) with a Neural Network (MMF-NN) framework to mitigate the influence of A0. Then we utilize the local window Multichannel Singular-Spectrum Analysis (MSSA) to suppress the effect of tool-casing multiples on the TIE. In the second step, we propose a sinusoid-search method with a path post-correction algorithm to automatically track the TIE arrivals from the enhanced TIE waveforms. Synthetic and field data results show that our TIE processing can effectively eliminate the A0 mode and suppress tool-casing multiples. Additionally, the picked TIE arrivals are consistent with actual TIE curves.