High Bandwidth Distributed Acoustic Sensing for Microcrack Detection
A. Turolla, Massimo Zampato, Sebastiano Correra, Luca Schenato, Luca Palmieri · International Petroleum Technology Conference · 2024
Abstract This paper presents a new system for distributed acoustic sensing (DAS, Hartog 2018 [3]). This system can continuously monitor structures along paths with a total length of several kilometers. It can detect fast impulsive events, such as those generated by microcracks, that can have a duration of around 1 μs. This is particularly useful for monitoring structures susceptible to microcrack phenomena, where traditional DAS systems may not be able to detect such short vibration events. This new system has many potential applications in predictive maintenance, including monitoring long structures like pipelines, tubulars for oil and gas wells, and wind turbine blades. The system relies on a novel Continuous Wave probing of the sensing fiber based on Orthogonal Frequency Division Multiplexing (OFDM, Schulze, Lueders 2005[3]), which is commonly used in digital television, DSL internet access, wireless and mobile communications. OFDM is used to continuously probe the sensing fiber and overcome the limitations imposed by the round-trip propagation time of the probe pulse in traditional DAS systems. With this method, the acoustic sampling rate can be increased beyond the traditional limit. This results in higher sensor bandwidth and greater efficiency in the system. Here, a theoretical model of the system is developed to define the hardware of the interrogator, formulate the algorithm for extracting the vibration signal from the optical signal, and evaluate the theoretical system performances. Subsequently, a lab-scale system prototype is designed and built to validate the soundness of the technique.