Fibre-optic based Distributed Acoustic Sensing (DAS), is now commonly used around the world for providing pipeline operators with real-time and early warning of intrusions on their pipeline Right of Ways. Also open to analysis within the DAS signal return are multiple signatures derived from the egress of product leaking from pipelines. Over the last three years, focussing attention on these alternative signals, OptaSense have developed a novel 4-mode External Leak Detection capability, fusing outputs from both DAS, Negative Pressure Pulse (NPP) and Distributed Temperature Gradient Sensing (DTGS) signals (the latter not to be confused with Distributed Temperature Sensing or DTS). The first commercially deployed 4-mode Leak Detection products are now being seen on the market, for both gas and liquids pipelines.
In this paper, we report how DAS can be used to provide these four modes of leak detection — including (listed in order of typical detection latency, fastest to slowest)
i) negative pressure waves created in the pipeline product from the leak event
ii) acoustic noise from turbulent flow through the leak orifice
iii) temperature gradients in the soil due to the presence of the leaked product (positive and negative), and
iv) local strain/ground heave due to soil displacement by the leaked product.
These acoustic, temperature and strain measurements using a fibre-optic cable buried next to a pipeline can be fused together to provide highly sensitive and reliable alerts for pipeline leaks. The pipeline industry has always sought to detect smaller leaks faster, with better locational accuracy. This paper, which draws upon industry sponsored test results and commercial deployment data, provides an update to the industry on leak detection possibilities using DAS.