Sensoriamento acústico e de temperatura distribuído - aplicações utilizando retroespalhamento Rayleigh e Raman em fibras ópticas

Abstract

This thesis expounds on the evolution of methodologies and techniques for enhancing fiber-optic distributed optical sensors, with a particular emphasis on industrial applications, particularly within the oil and gas sector. The objective of the work is to enhance the measurement capabilities of distributed acoustic sensing (DAS) and distributed thermal gradient sensing (DTGS) systems, both of which are based on the Rayleigh backscatter phenomenon, as well as distributed thermal sensing (DTS) systems that are based on Raman backscatter. The emphasis is on increasing the sensitivity, accuracy, and frequency response of these sensing systems. A comprehensive theoretical review of the state-of-the-art fiber-optic distributed systems is initially presented, highlighting their applications in challenging industrial environments. In the following section, the physical and operational principles of DAS, DTGS, and DTS systems will be delineated, with a particular emphasis on the measurement techniques of optical phase time-domain reflectometry (φ-OTDR) and Ramam OTDR. One of the advances presented is the proposal and implementation of an acousto-optic amplifier designed to increase sensitivity to acoustic signals in DAS systems. This contributes to more accurate and reliable acoustic detection. Another significant contribution is the theoretical and experimental understanding of the limitations in reconstructing dynamic deformations and thermal variations measured in DAS and DTGS systems. This work presents a detailed analysis of the acquisition and excitation parameters required to optimize the measurement of these physical quantities. Furthermore, a set of temperature correction techniques based on analytical heat transfer models using Kalman filters have been developed and evaluated. The work presents techniques for integrating DAS and DTS systems to enable the simultaneous measurement of acoustic and thermal parameters in separate optical fibers in the same cable, or even in the same optical fiber. The following text is intended to provide a comprehensive overview of the subject matter. The implementation of a data fusion technique is also a feature of the system, and it is this feature that enables the improvement of the thermal measurement of the hybrid system under discussion. Absolute temperature measurements with rapid temporal updates are thus enabled. The findings indicate the viability of these technologies in enhancing the oversight of pivotal industrial processes, including oil well monitoring and leak detection, thereby ensuring enhanced safety and operational efficiency.