The Distributed Acoustic Sensor (DAS) used here (Parker et al., 2012), allows both the amplitude and the phase of acoustic signals to be continuously recorded along a length of optical fiber. In this paper, non-intrusive flow metering based on the use of this sensor is performed for different pipe sizes and flow conditions. By wrapping a continuous length of fiber helically around the exterior pipe, the system measures the dynamic radial strain (hoop strain) along a pipe with a spatial resolution on the order of millimeters and a time resolution on the order of tenths of milliseconds. As a result, this implementation of the sensing system output makes it possible to visualize the generation and convection of eddies by using a waterfall plot of distance versus time. By analyzing the recorded data using a frequency-space transformation (f-k plot), it is possible to determine precisely both the speed of eddies, as well as the speed of sound.
This paper will present experimental results from single- and multi-phase tests to demonstrate the applicability of the technology to the monitoring of fluid velocity and the determination of flow composition. It will be seen that the system, which can be installed unobtrusively, is straightforward to apply for several types of commonly encountered flow regimes. Further, this paper will also consider several practical aspects regarding the installation and use of such a system in the oilfield. Finally, it will be shown how multiple monitoring zones can be incorporated using a single optical fiber. It will be seen that this system is non-intrusive and can be retrofitted to existing pipes to monitor the flow simultaneously at multiple locations for accurate flow profiling and characterization.