Gas pipeline leak noise measurements using optical fibre distributed acoustic sensing

Leakage from pipes is a major issue in both the oil and gas sectors, not only in environmental and economic terms, because of wasting important natural resources, but importantly from a safety perspective. Optical fibre technology offers the possibility of continuous acoustic monitoring of pipelines and remote detection of leaks. In this paper we present results from gas leak measurements made on a specially designed, buried pipeline test rig, for which leak energy radiated directly from the leak (orifice noise) dominates over energy radiated from the pipe wall. Measurements of the orifice noise are made using an optical fibre distributed acoustic sensing system as well as conventional geophones. Both the geophones and the optical fibres are shown to be able to detect the orifice noise, particularly when the fibres were located close to the pipeline. Fibre measurements are found to be limited by both high background noise and by gauge length, which limited the upper frequency limit for accurately determining the phase of the ground response. The measurements indicate that the orifice noise sets up Rayleigh waves in the ground, largely contained in frequencies below 100Hz, the magnitude of which are found to be compatible with predictions from idealised jet theory. The effect of fibre ducting and armouring is also evaluated.