Projeto e aplicação de um sistema de sensoriamento acústico distribuído baseado em OTDR sensível à fase

Abstract

Distributed Acoustic Sensing Systems (DAS) have recently experienced significant investment and research efforts, having found several applications, especially in oil and gas industry. Applications range from pipeline integrity and leakage monitoring to intruder detection, seismic assessments and beyond. Schemes based on Phase-Sensitive Optical Time-Domain Reflectometer (Φ-OTDR) have shown effectiveness in detecting vibration events along optical fibers, especially concerning the response linearity obtained by phase measurements of the backscattered signal. Among the various schemes proposed in the literature, the heterodyne detection method has shown to be promising due to the simplicity of implementation, involving a smaller number and complexity of components. In this work, a DAS system based on heterodyne detection is developed. A mathematical model was implemented and validated through comparison with real results obtained with the equipment developed. The results promote a discussion about the DAS signal chain, focusing on the optimization of acquisition parameters such as the gauge length, on the concept of spatial resolution and its implication in the ability to resolve disturbances in the fiber, and also on the demonstration of undersampled measurements, exploring important constraints inherent to the correspondence between acquisition and processing parameters. Finally, the DAS system developed has its capabilities proven in field tests for measurements in two applications directly related to the oil and gas industry. In the first one, DAS was deployed in a 90 m deep borehole, allowing remote monitoring of a submersible pump and measurements of simulated seismic activities. In a second field test campaign, multiphase flow measurements were performed in a horizontal pipe using the DAS system. Among the parameters evaluated, it focuses on measurements of bubble velocities through radial integration in k-f space and distributed cross-correlation. The results showed significant similarity in relation to the expected theoretical values and measurements using a reference conductance-based phase meter. The results validate the feasibility of the DAS system developed for oil and gas industry applications.