Recent advances and challenges of cement bond evaluation based on ultrasonic measurements in cased holesOA

Cement bond quality evaluations are essential for assessing zonal isolation between formation strata,providing crucial information for ensuring environmental and ecological safety in oil and gas exploitation,geothermal energy injection and geological carbon dioxide sequestration.In the past decade,the ultrasonic pulse-echo and pitch-catch logging techniques have emerged as effective and non-destructive methods for quantitatively eval-uating bond quality at both the casing-cement and cement-formation interfaces.This review presents a comprehensive overview of recent advancements in cement bond quality assessment based on ultrasonic mea-surements.Key developments include automatic waveform quality assessment,inversion techniques for mud and cement impedance,tool trajectory corrections,separation of flexural and extensional mode waves,machine learning-based extraction and enhancement of TIE waveforms,and imaging of the cement-formation interface using the reverse time migration approach.The review thoroughly explores the methodological principles and applications of these techniques,supported by synthetic datasets,full-scale physical well experiments,and field well data.Considering the recent progress in machine learning and the growing availability of advanced computational resources,we highlight the most significant achievements and ongoing challenges in data pro-cessing,while discussing the potential advancements these techniques could offer in the near future.