Many variants of pipeline line leak detection systems are in operation today on liquid or gas pipelines. These often rely upon a single leak detection methodology. This could include; CPM, Mass Balance, Acoustic, Flow or Temperature Monitoring. Latest developments in fibre optic technology now mean that a number of these methods can be combined in a single system. Fibre Optic Distributed Acoustic Sensing (DAS) is able to use the following measurands to detect within leaks seconds with a location accuracy of 10 meters. DAS detects the following signatures of a leak; Acoustic Anomaly; Temperature Gradient, External Ground changes and Negative Pressure Pulse. By fusing these signatures together DAS is able to provide a sensitive yet robust and reliable leak detection solution. Added benefits of the system are also the traditional security aspects that help prevent as opposed to detect pipeline damage as well as Inline Inspection Gauge Tracking through the same hardware set. This paper examines the methodologies used to detect leaks in all phases of products. Discusses the industry led tests conducted so far and provides real life evidence of leaks detected in the field.
Unbonded flexible risers are a critical part of offshore field architecture bringing oil and gas from seabed to platforms on the surface. A failure in operation will result in stop of production and hence a significant loss of revenue. Risers are subject to a number of loading issues including internal and external pressure, vessel motions and current and wave actions. As a result, risers, endure significant strain levels which can impact on their integrity and functionality. The recent implementation of fiber optic monitoring embedded in flexible risers, is an important step towards turning risers into inspectable structures. The embedded monitoring systems ensure the asset can operate safely at its optimum level for the maximum period of time. The combined use of optical point sensors and fully distributed sensors allow various events to be monitored. This includes breach of outer sheath, condensate build up, polymer temperature, pipe temperature during shut in, fatigue and wire break. The traditional industry method for combating these issues has been extensive onshore testing on small sections of the riser allowing the operator to build up a bank of fatigue and reliability data which is used to statistically forecast the strains and stresses the riser will encounter. This data takes into account expected changes throughout the lifecycle of the riser, such as material degradation and environmental issues including storms and hurricanes. The main inspection method in operation to back this up has been expensive inspection campaigns by diver or ROV focusing on external damage. New advances in optical technology and riser manufacturing techniques mean that a suite of real-time monitoring can provide a far more accurate picture of a riser's condition during operation. This improves decision making by allowing structural and temperature issues to be detected at the earliest possible stage and rectified in the most efficient manner, ensuring risers satisfy safety and regulatory requirements and help maximize oilfield productivity. The enabled condition dependent maintenance of risers will reduce the need for expensive ROV operations for inspection. Real time riser monitoring is set to play an increasingly important role as the operators start to insist on the adoption of this technology in the risers delivered to them. As oil production reaches into deeper and deeper water depths, the real time understanding of the integrity of the risers will become paramount. This paper details the advances that have been made in optical monitoring and visualization techniques and their application within the intelligent riser.
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.
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