Use of optical fibre distributed sensing technologies is increasing in the field of pipeline monitoring, providing measurements for a variety of structural and operational metrics, including temperature, strain, vibration, and acoustics.
Distributed acoustic sensing (DAS), has primarily been utilised for the purpose of security monitoring. Specifically when considerate of utilising optical fibre cables that traverse parallel and in the near vicinity of buried pipelines, with systems commissioned to identify threat based environmental activities.
The technology comprises an interrogator, connected to a single-mode optical fibre cable, which interrogates the optical fibre to acquire coherent Rayleigh backscatter. Localised environmental vibration and acoustic perturbations result in a proportional strain of the fibre. Such strain results in a localised optical path length variation, leading to phase changes in the measured signals. Signal processing techniques are subsequently applied to infer the characteristic of the originating stimulus, and thus identify and locate the acoustic activity of interest. Activity may arise as a result of ground excavation, vehicular movement, or tapping activity in the near vicinity of the pipeline. The technology provides a measurement resolution of the order of 1.0m, spatial resolution of the order of 10.0m, will operate on optical fibre lengths of =100km, with an acoustic bandwidth ranging from 1Hz to 1kHz (for the stated fibre length).
Recently DAS developers have been commissioning systems for the purpose of leak detection monitoring. Demonstrating the technology responds positively to stimulus associated with leaks. Specifically dynamics associated with orifice noise, pressure wave propagation, and thermal variations. It's additionally hypothesised that it may be possible to utilise DAS to identify dynamics associated with ground heave, in the event of low leak rate. This paper presents review of such capability, utilising experimental apparatus to simulate fibre strain associated with ground heave resulting from a small joint or corrosion type leak.