Measuring Flow in Pipelines via FBG and DAS Fiber Optic Sensors

Abstract

An investigation is made into the use of a fiber optic sensing system for monitoring and measuring fluid flow in pipes. This is done using two fiber optics sensing systems, a Distributed Acoustic Sensing "DAS" system and a Fiber Bragg Grating "FBG" system. A laboratory setup is used to conduct these tests and the setup is structured to simulate an offshore environment. The laboratory setup consists of a water reservoir that flows water through PVC pipes into a tank, fibers are attached to the pipes, and a flow meter is used to measure the flow rates. From the conducted flow experiments, a relationship between flow rates, DAS amplitudes, and FBG wavelength shifts is built. This paper presents the response of fiber optic sensing systems to flow experiments that were conducted with various flow rates, and simulated leak tests with and without flow. The results are used to establish a relationship between the fiber optic response and flow variation, to develop a method of measuring flow rates via the fiber optic systems. Such that any pipes equipped with fiber optics could be used to measure approximate flow rates. This study finds a strong correlation between the fiber optic sensing systems measurements and measured flow rates. In the FBG system, flow was found to have two influences on the FBG measurement; an increase in flow shows an increase in the FBG sensor wavelength, also, the turbulence of flow was found to be proportional to the amount of fluctuations in the FBG measurements. Such that wavelength shifts of up to 120 picometers are visible for an average flow rate of 27±0.1 Gal/min. With the DAS system, the amplitude response shows a stronger relationship to the turbulence of flow rather than the average flow rate. Such that the highest amplitude response during a flow test would always correspond to the flow valve being half open (which was found to be the most turbulent flow). In conclusion, this study indicates that fiber optic sensing systems can be used on pipelines and well casing to monitor and measure flow. Additionally, it demonstrates that taping the sensors on the pipe is enough to capture the signal produced by fluid flow in a pipe. The relationship provided between the FBG measurements and flow rates can be used to compute approximated flow rates when using an FBG sensing system to monitor flow.