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Many pipelines are built in regions affected by harsh environmental conditions where changes in soil texture between winter and summer increase the likelihood of risks. Pipeline routes also cross the mountains that are characterized by steep slopes and unstable soils as in the Andes and along the coastal range of Brazil. In other cases, these pipelines are laid in remote areas with significant seismic activity or exposure to permafrost. Depending on weather conditions and location, visual inspection is difficult or even impossible and therefore remote sensing solutions for pipes offer significant advantages over conventional inspection techniques. Optical fibers can help solve these challenges. Optical fiber based geotechnical and structural monitoring use distributed measurement of strain and temperature thanks to the sensitivity of Brillouin scattering to mechanical and thermal stresses. The analysis of scattering combined with a time domain technique allows the measurement of strain and temperature profiles. Temperature measurement is carried out to control soil erosion or dune migration through event quantification and spatial location. Direct measurement of strain in the soil also improves the detection of environmental hazards. As an example the technology can pinpoint the early signs of landslide. In some cases, pipe actual deformation must be monitored such as in case of active tectonic fault crossing. Pipe deformation monitoring operation is achieved by the measurement of distributed strain along fiber sensors attached to the structure. This paper comprehensively reviews over 10 years of continuous development from technology qualification and validation to its implementation in real cases as well as its successful continuous operation. Case studies present pipeline monitoring in Arctic and Siberian environment as well as in the Andes. They illustrate how the technology is used and demonstrate proof of early detection and location of events such as erosion, landslide, subsidence and pipe deformation.

Submillimeter crack is detected with a dedicated fiber-optic strain cable, a 1-m-spatial-resolution (w) distributed Brillouin sensor and an advanced signal processing technique. The signal processing approach consists in spectrum shape analysis and multiple peaks detection.

We demonstrate that BOTDA is the equipment of choice for Distributed Temperature Sensing (DTS) when challenging components such as Wet Mate Connectors (WMC) and Fiber Optic Rotary Joints (FORJ) are inserted in the sensing line. The parameter of Temperature Measurement Dead Zone (TMDZ) is introduced to support the discussion and quantify possible impairments. A laboratory qualification test with real FORJ and WMC is conducted confirming the theoretical expectations. The system is then implemented offshore demonstrating that FORJ and WMC do not affect the sensing operation in field environment.

The concern of the pipeline industry and general population for a safe and green environment is higher than ever. This highlights the need for efficient leak detection to prevent environmental catastrophes and operational disruption. Therefore, accurate techniques to detect and locate very small leaks that could develop into larger leaks are a valuable asset for the construction of key pipelines. External pipeline leak detection systems based on distributed fiber optic sensing emerge as the most appropriate solution for automatic detection and localization of very small leaks. In the case of the Kinosis pipeline system, two 11km Electrically Heat Traced Pipe-In-Pipe (EHTPIP) pipelines have been built between the Nexen Long lake upgrader and Nexen Kinosis SAGD facilities. The fiber optic sensing cable is directly in contact with the EHTPIP external surface. These pipelines carry Produced Emulsion and Boiler Feed Water at temperatures as high as 120°C and 150°C respectively. The fiber optic distributed sensing system provides temperature feedback information to the operator, not only in operation and in case of a leak but also when the Electrical Heat Trace system is turned on; in this case, the monitoring system can detect and locate overheating problems and/or signs of heating failures. In the case of a leak, the outer temperature of the pipeline will increase; this will automatically be detected and monitored by the DITEST temperature monitoring system and will trigger an alarm to the Nexen LONG LAKE upgrader SCADA system for that specific location. Furthermore, the combination of fiber optic distributed monitoring with the PIP technology enables to detect and locate a leak in the inner pipeline at a very early stage, therefore avoiding any environmental damage (the leak is still contained by the outer PIP tube) and giving time to the pipeline operator to plan a sectional replacement.

A novel scheme is proposed to extend the sensing range of Brillouin optical time-domain analyzers (BOTDA). Specially-designed erbium doped fiber amplifier (EDFA) repeaters are located every 65km fiber along the sensing cable to achieve a total sensing length of 325km, corresponding to a 650km loop. At the end of the sensing fibre, we experimentally demonstrated a measurement repeatability of 2°C (2Ϛ ) using a three meters spatial resolution.

The present work introduces the technology background at the origin of FOPIMS (Fiber Optic Pipeline Integrity Monitoring Systems) with an emphasis on geotechnical monitoring. It shows how temperature sensing can be implemented to control soil erosion or dune migration through event localization and spatial quantification. Arctic pipeline monitoring project illustrates the application of soil erosion detection. Direct measurement of strain in soil also enhances environmental threat detection. Combined with temperature sensing, strain sensing composes the geotechnical monitoring system. Transandean pipeline monitoring examples are presented where the DITEST AIM was implemented for geohazard prevention. These study cases concern new pipeline installation as well as retrofit of existing lines. The technique successfully evidenced early events and allowed preventive measures to be taken. In some applications actual pipeline deformation need to be monitored. Such operation is achieved by measuring distributed strain along sensing cables attached to the structure. We show how such measurements complement the geotechnical measurements. We also describe a real implementation in seismic active area. As a whole, the work focuses on the technique principles, the installation and how the system is being implemented for pipeline preventive maintenance. We intend to present a comprehensive set of design guidelines based on real results and lessons learned from the various projects in what concerns geohazard detection and pipeline deformation monitoring.

During the past 10 years, the oil and gas industry has gained confidence in the capabilities and the reliability of Fiber Optic Distributed Sensing (OFDS). Real world implementation can be found in both downstream and upstream branches. For example, at one end of the industry spectrum, service companies have started to use Distributed Temperature Sensing (DTS) for in-well temperature monitoring to optimize oil recovery processes. At the other end, pipeline operators have installed pipeline integrity monitoring systems based on Distributed Temperature and Strain sensing (DITEST) to fulfill realtime monitoring of soil stability, pipeline 3D deformation and leak detection. The use of OFDS for offshore structure integrity monitoring such as flow lines, risers and umbilicals has been qualified and field tested already whereas other applications such as performance rating of power umbilicals and enhanced flow assurance system using OFDS are being evaluated. Currently, the offshore full scale implementation of OFDS technologies still faces challenges of its own. In particular, sensor integration into the structure to be monitored is a minimum requirement which applies to any OFDS. If fiber optic is a common mean of data transmission, subsea conditions imply the use of specific components such as Wet Mate Connectors (WMC) and Fiber Optic Rotary Joints (FORJ). These components present large insertion and return loss characteristics for which OFDS require special attention to the OFDS system to comply with such characteristics. The effect of these components is twofold. First it impacts the sensor optical budget limiting its measurement range. Second, sensor sections remain completely blind due to the high reflection levels leaving the structure without status information over distances that can be as large as several kilometers. The present works describes how the DITEST based on Stimulated Brillouin Scattering (SBS) can overcome the limitations imposed by both WMC and FORJ components and fully comply with SURF monitoring requirements. The ability of the DITEST is justified theoretically and demonstrated experimentally through qualification trials involving hotspot detection while WMC and FORJ are part of the sensor path. Their effects are quantified through the determination of the measurement dead zone (shorter than 4m), the temperature uncertainty and the resolution. The work also reports the subsequent installation on operational structures as these trials were successful. The DITEST has been installed to continuously monitor the temperature of a 3km long power umbilical and control the heating system of subsea rigid flowlines whose length can be as large a 45km.

Asset integrity monitoring based on distributed fiber optic monitoring using BOTDA is playing an increasingly important role in today’s oil and gas and energy industries. Existing applications, part of operator’s asset integrity management plans are as diverse as fatigue monitoring of subsea umbilicals, thermal optimization of direct electrical heated subsea flowlines, pipeline leak and ground movement detection and 3D pipeline deformation monitoring or thermal management of offshore wind farm electrical export cable. The monitoring solutions developed and qualified by OMNISENS over the last decade are now installed world wild, providing 24/7 event detection and localization for its valuable customers.

Hydrate and wax formation in subsea flowlines is a major cause of production impairment. Among various approaches used to minimize the risk, Direct Electrical Heating (DEH) is being applied. DEH is based on passing a current through the pipe wall to mitigate heat losses from the fluid to the surroundings during events which require flow assurance measures. The Piggyback Cable, a high voltage cable attached to the DEH pipeline, is during operation exposed to thermal and mechanical loads which may be critical for the integrity of the DEH system. The overall safety requirement is that any potential Piggyback Cable fault is detected and disconnected from the power source before damage is caused to the pipeline. Conventional cable fault detection methods based on current measurements give adequate protection for the main part of the pipeline. However, for the far end of the Piggyback Cable complementary fault detection is required. A method based on fiber break monitoring has been qualified for this purpose. The new method is implemented in the North Sea on two DEH pipelines operated by Statoil, 43 and 21 km long respectively. The protection is facilitated by standard single-mode fibers integrated into the DEH cables. Although not basis for the design the integrated fibers open up possibilities for temperature and strain sensing using stimulated Brillouin scattering. Sensing has been performed on a 43 km DEH pipeline using the DITEST AIM (Distributed Temperature and Strain Asset Integrity Monitoring). Analysis of the sensing results reveal that distributed fiber optic sensing is capable of pin-pointing thermal events and strain induced loads for an object of this length.

Operating in remote regions, Russian pipelines not only are subjected to harsh environmental conditions, but also in some of their sections to seismic activity. In order to secure these assets’ integrity, monitoring is mandatory. Due to the long distances to be monitored and to the linear nature of these pipelines, distributed fiber optic sensing is the only solution to provide remote monitoring operation with accurate localization of events. In some cases, it can even take advantage of the telecommunication fibers laid along the pipelines to minimize installation cost. A complete and commercially available solution based on the DITEST Asset Integrity Monitoring (AIM) system combines strain and temperature measurement over 100’s kilometers at meter spatial resolution with dedicated fiber optic cables specifically developed for strain, temperature and ground movement measurement to provide continuous information on any abnormal pipeline behavior, including leak, intrusion, excessive tube deformation and seismic activity. This scalable monitoring solution was adopted to monitor the most critical areas of the Sakhalin-Khabarovsk-Vladivostok pipeline route, which crosses 32 Active Tectonic Faults (ATF) zones. A combination of pipeline deformation monitoring, ground movement detection and leak detection is used to monitor these critical pipeline regions. The early knowledge of abnormal events allows the pipeline owner/operator to take preventive mitigation measures in response to these critical geohazards.

This paper describes the outcome of two groups which are involved in the specification of guidelines for fibre optic sensors performance and testing. The "Guideline for use of fibre optic sensors" from the COST-299 guideline group, and the "Optical Strain Sensor based on Fibre Bragg Grating" from the GESA guideline group of the VDI - "The Association of German Engineers". Through appropriate specifications and definitions, both guidelines aim at enabling better understanding of fibre optic sensors characteristics and performances. A concise view into the structure of the guidelines is presented, emphasizing important aspects. The English version of the two guidelines will be available in autumn 2009.

An increasing number of pipelines are constructed in remote regions affected by harsh environmental conditions where pipeline routes often cross mountain areas which are characterized by unstable grounds and where soil texture changes between winter and summer increase the probability of hazards. Third party intentional interference or accidental intrusions are a major cause of pipeline failures leading to large leaks or even explosions. Due to the long distances to be monitored and the linear nature of pipelines, distributed fiber optic sensing techniques offer significant advantages and the capability to detect and localize pipeline disturbance with great precision. Furthermore pipeline owner/operators lay fiber optic cable parallel to transmission pipelines for telecommunication purposes and at minimum additional cost monitoring capabilities can be added to the communication system. The Brillouin-based Omnisens DITEST monitoring system has been used in several long distance pipeline projects. The technique is capable of measuring strain and temperature over 100's kilometers with meter spatial resolution. Dedicated fiber optic cables have been developed for continuous strain and temperature monitoring and their deployment along the pipeline has enabled permanent and continuous pipeline ground movement, intrusion and leak detection. This paper presents a description of the fiber optic Brillouin-based DITEST sensing technique, its measurement performance and limits, while addressing future perspectives for pipeline monitoring. The description is supported by case studies and illustrated by field data.

Sub-millimeter crack is detected with a dedicated fiber optic strain cable, a 1 m spatial resolution (w) distributed Brillouin sensor (DBS) and an advanced signal processing technique.

Local beat length with a 21.5cm spatial resolution is measured in one second along a single mode fibre using the polarisation dependence of stimulated Brillouin scattering, in a non-destructive and simple way.

A new and compact photoacoustic sensor for trace gas detection in the 2-2.5 μm atmospheric window is reported. Both the development of antimonide-based DFB lasers with singlemode emission in this spectral range and a novel design of photoacoustic cell adapted to the characteristics of these lasers are discussed. The laser fabrication was made in two steps. The structure was firstly grown by molecular beam epitaxy then a metallic DFB grating was processed. The photoacoustic cell is based on a Helmholtz resonator that was designed in order to fully benefit from the highly divergent emission of the antimonide laser. An optimized modulation scheme based on wavelength modulation of the laser source combined with second harmonic detection has been implemented for efficient suppression of wall noise. Using a 2211 nm laser, sub-ppm detection limit has been demonstrated for ammonia. © 2005 Elsevier B.V. All right reserved.

The monitoring of temperature profiles over long distance by means of optical fibers represents a highly efficient way to perform leakage detection along pipelines, in dams, dykes, or tanks... Different techniques have been developed taking advantages of the fiber geometry and of optical time domain analysis for the localization of the information. Among fiber optics distributed temperature sensing techniques, Brillouin-based systems have demonstrated to have the best potential for applications over distances up to several tens of kilometers. The key features and performances are reviewed in the present article and a 55km pipeline equipped with a fiber optics leakage detection system is presented as a case study.

Summary form only given. The nonlinear refractive index has drawn considerable attention these past few years, because it may significantly perturbate long-range propagation of lightwaves in optical fibers. Two main origins to this nonlinearity have been identified: nonresonant electronic nonlinearity and electrostriction. This paper shows that the electrostrictive contribution to the nonlinear refractive index n, may indeed be straightfowardly calculated from Brillouin gain measurements. The Brillouin linear gain g, is dependent on material properties and in particular on the electrostrictive coefficient.

Distributed fibre-optic sensors that rely on Brillouin scattering are being used by the oil and gas industries to keep their infrastructure safe and working properly.

Long-range distributed strain and temperature measurements along an optical fiber is presented, using a novel optical sensor based on stimulated Brilloum scattering. The optical effect only depends on the fiber material, so that the bare fiber itself acts as sensing element without any special fiber processing or preparation. The sensor accuracy is 1°C for temperature and 20 ic for deformation. The spatial resolutionis 1 meter and the sensor range is more than 20 km. Successful monitoring of a concrete dam element hasbeen performed using an embedded standard cabled fiber. The temperature dynamics of lake waters havebeen also observed by simply laying a cable over the lake bed.Keywords: distributed sensor, optical fiber, strain sensor, temperature sensor 1. INTRODUCTION A novel optical sensor for long-range distributed strain and temperature measurements along an optical fiber is presented, based on a nonlinear effect called stimulated Brilloum scattering. This interaction causes

Long-range distributed strain and temperature measurements along an optical fiber is presented, using a novel optical sensor based on stimulated Brillouin scattering. The optical effect only depends on the fiber material, so that the bare fiber itself acts as sensing element without any special fiber processing or preparation. The sensor accuracy is ± 1°C for temperature and ± 20 µe for deformation. The spatial resolution is 1 meter and the sensor range is more than 20 km. Successful monitoring of a concrete dam element has been performed using an embedded standard cabled fiber. The temperature dynamics of lake waters have been also observed by simply laying a cable over the lake bed.

In this paper, we discuss the fundamental limitations of the SBS analysis as a distributed sensing method when the spatial resolution is in the meter range. We also present a novel experimental configuration that reaches the best performances achievable for this kind of sensors.

Brillouin-gain-spectrum measurement along an optical fiber has recently gained a lot of interest owing to its potential for strain monitoring in installed cables and for distributed temperature sensing. We present a method that has the following advantages: (1) few optical elements are required, (2) a single laser source is used, and (3) a single fiber end is accessed. A schematic diagram of the experimental setup is shown. The operation of this setup relies on two features. First, the pump and probe signals are pulses that both propagate back and forth through the fiber by using a reflection at the far end. The second and more important feature is the use of a guided-wave intensity modulator for pulsing the laser light to form the pump signal and for generating the probe signal

A novel configuration of a distributed fiber sensor by Brillouin gain analysis has been developed for temperature and strain monitoring. It uses a single laser source, and the required light signals are all generated with an electro-optic modulator, resulting in high stability and excellent reliability of the measuring setup. Measurement of the induced strain in a wound fiber is presented as a demonstration of the system performance.

A simple system for optical and microwave signals analysis based on the optical sampling technique is presented. It is novel in requiring only low-frequency detection and electronic components. This is made possible by the use of a commercially available LiNbO3 intensity modulator for processing the light wave. The ultimate performance of the system is discussed, and comparisons with standard detection systems are also made

Sub-ppm hydrogen chloride (HCl) and water vapour (H2O) monitoring using photoacoustic spectroscopy in optical fibre manufacturing is reported. The development and performance of a sensor based on an acoustic resonant configuration is described, and on-site measurements are presented. Two DFB lasers emitting in the 1370 nm and 1740 nm range were used for the detection of H2O and HCl, respectively. A detection limit (defined for a SNR=3) of 60 ppb for HCl and 40 ppb for H2O was achieved. Contamination sources of the carrier gas used for the fibre preform manufacturing are identified and discussed. © Springer-Verlag 2006.

A novel method for Brillouin gain spectrum measurements in optical fibers is presented. It is based on the pump and probe technique with the specificity to use a single laser source together with an external modulator to generate the interacting lightwaves. The high accuracy and inherent stability of the technique makes it suitable for calibration and reference measurements. Different fibers with different refractive index profiles have been tested and characterized. The problem of the evolution of the polarization of the interacting waves is addressed in the article and a polarization insensitive determination of the actual Brillouin gain coefficient is made possible through two successive measurements with different polarizations. The effects of strain and temperature on the Brillouin gain spectrum are also fully characterized.

A novel configuration is presented here, based on the pump and probe technique, that has the following advantages: 1) few optical elements are required, 2) a single laser source is used, 3) a single fiber end is accessed, 4) only pulsed signals propagate.

Abstract The paper describes first the laboratory and qualifications works that were conducted to implement Distributed Fiber Optic Sensors (DOFS) such as Distributed Temperature and Strain Sensing (DTS/DSS) technologies in umbilicals. It also shows how these technologies have been implemented in the field for umbilical thermal and mechanical stresses monitoring. There is value to use DFOS for offshore structure integrity monitoring such as flow lines, risers and umbilicals. Other applications such as rating of power umbilicals, flow assurance or downhole sensing would help optimize field production as well. Currently, the offshore full scale implementation of DFOS technologies still faces challenges of its own. In particular, sensor integration into the structure to be monitored is a minimum requirement which applies to any DFOS. If fiber optic is a common mean of data transmission, subsea conditions imply the use of specific components such as Wet Mate Connectors (WMC) and Fiber Optic Rotary Joints (FORJ). These components present large insertion and return loss characteristics which are detrimental to most of the DFOS. The effect of these components is twofold. First it impacts the sensor optical budget limiting its measurement range. Second, sensor sections remain completely blind due to the high reflection levels leaving the structure without status information over distances that can be as large as several kilometers. The present works describes how DTS/DSS based on Stimulated Brillouin Scattering (SBS) can overcome the limitations imposed by both WMC and FORJ. The DOFS ability is justified theoretically and demonstrated experimentally through qualification trials involving hotspot detection while WMC and FORJ are part of the sensor path. Their effects are quantified through the determination of the measurement dead zone (shorter than 4m), the temperature uncertainty (better than 0.5K) and the resolution (below 0.5K while the measurement time remained unchanged (tens of seconds to minutes). The work also reports the subsequent installation on operational structures as these trials were successful. The DOFS has been installed to continuously monitor the temperature of a 3km long power umbilical and control the heating system of subsea rigid flowlines whose length can be as large a 45km. Introduction The increasing demand for energy supplies leads operators to explore and exploit remote and deep offshore oil fields. These marine fields often lay in tropical regions where permanent platforms are exposed to severe hurricanes threatening their integrity. Moreover currently exploited marine oil fields become more and more depleted. These conditions cause two major challenges to the operators. First, oil being extracted from an offshore reservoir must be processed at the sea bottom. Processing at the wellhead consists in separating all the phases present in the extracted product. Moreover extended operation of depleted oil reservoirs requires higher pumping powers. Both tasks imply that large powers (>1MW) are supplied to the subsea pumps via the umbilical. Thermal stress is very high, in particular in the splash zone and near the buoy where all umbilical and oil risers are converging, creating a hot spot. This is a particularly critical issue as many offshore fields are located in hot water seas (west coast of Africa and Australia, east coast of Brazil) which strongly limit heat dissipation. It is common to inspect subsea structures with Remotely Operated Vehicles (ROV's). The method is however expensive and unreliable since visual inspection is only capable of detecting external anomalies and is unable to detect internal structural deterioration. Moreover it does not give any information on how the structure is affected when operational conditions are changed. In particular, hot spot and abnormal temperature changes cannot be detected.

Sub-ppm (HCl) and (H2O) monitoring using photoacoustic spectroscopy is reported in optical fibre manufacturing for the production of low-water-peak fibres. Contamination sources of the carrier gas used for fibre preforms manufacturing were identified and discussed.

An ammonia traces analyser based on photoacoustic spectroscopy is described. The system uses a CO2 laser and a properly designed resonant photoacoustic cell to achieve ammonia detection at sub-parts-per- billion (ppb) level. The instrument features unattended automatic on-line monitoring of ammonia with a detection limit of 0.1 ppb. Interferences from atmospheric CO2 and H2O are efficiently suppressed by a careful selection of the laser wavelength and a compensation of the water vapour signal made with a high-precision hygrometer. The cell design enables continuous measurement at high flow rates (up to 51/min), which guarantees a fast response time of the system for the monitoring of ammonia, a sticky polar molecule that adheres to most surfaces. Various examples of applications of the instrument in the semiconductor industry and for atmospheric pollution monitoring are presented. They demonstrate the excellent performances of the system and its suitability for these applications. © 2004 Elsevier B.V. All rights reserved.