The risk associated with third-party damage to transmission pipelines in areas of urban development is high. Distributed monitoring is a modern technique that uses fiber optic cables as sensors to continuously monitor pipeline parameters such as acoustics, vibration, strain and temperature. The fiber optic system notifies the operator in real-time of ongoing events allowing decisions to be made to prevent external interference or quickly address an incident that has already occurred. Traditional methods used to install distributed monitoring systems on pipelines have limitations and are not feasible for all transmission pipelines. For instance, it can be both challenging and expensive to trench in fiber optics in developed areas and other installation techniques require the pipeline to be temporarily taken out of service. SaskEnergy Incorporated’s transmission line subsidiary, TransGas Limited partnered with a Canadian pipeline monitoring service provider to install fiber optics inside of a natural gas transmission pipeline using a pig, steel capillary tubing and a pack-off hanger. A disengagement system was incorporated to release the fiber optics after the desired monitoring distance was reached. It was decided to perform the pilot project on a newly constructed NPS 6 natural gas transmission pipeline located in Humboldt, Saskatchewan. Nitrogen was used as a medium to simulate an in-service pipeline in order to reduce the risks associated with the first attempt of the project designs. The fiber optics were inserted into steel capillary tubing and connected to a disengagement system located at the back of a pig. A pack-off hanger was used to maintain pipeline pressure during and after the installation was completed. The spool holding the steel capillary tubing was stopped once the maximum monitoring distance was reached and the differential pressure activated the disengagement system located at the back of the pig. The pig continued to the receive location and the fiber optics remained in the pipeline for continuous monitoring. The deployment was successful and the fiber optics will remain in the pipeline for a one (1) year monitoring period. The primary limitation to this pilot project was the strength of the steel capillary tubing. The steel capillary tubing’s ultimate tensile strength would have to be higher to accommodate a pipeline with a larger outside diameter, multiple bends, large changes in wall thickness or large elevation changes. In addition, the steel capillary tubing must be removed from the pipeline in order to perform pigging activities.

Unbonded flexible pipe is widely used in the oil and gas industry for its good flexibility, especially in deepwater oil and gas transportation. And the fiber reinforced unbonded flexible pipe has excellent corrosion resistance and wear resistance. However, they are subjected to internal pressure, external pressure and tensile loads during the service process, which are important factors affecting the integrity and security of the flexible pipe. In this paper, the mechanical behaviors of an 8-inchs fiber reinforced unbonded flexible pipe used in offshore gas development which consists of internal layer, internal pressure reinforcement layers, anti-wear layers, external pressure armor, tensile reinforcement layers and outer sheath is investigated by numerical methods. A rigorous three-dimensional solid finite element model of flexible pipe that considers the real material parameters, structural nonlinearity as well as the nonlinear contact behavior was created. ABAQUS/Explicit quasi-static simulation is adopted to study the mechanical behaviors of the flexible pipe under combined load. And the accuracy of the simulation method for the fiber reinforced layers such as internal pressure layer is verified by comparing with the small-scale internal pressure burst test of 1-inch flexible pipe. The mechanical behavior of flexible pipe subjected to internal pressure, external pressure and tensile load was investigated in detail. Based on the contrastive analysis, some practical conclusions have been obtained which may be used for the practical design and production of flexible pipe. This study can be referenced for the applications of unbonded flexible pipe in marine oil and gas production.

External Leak Detection systems based on distributed fiber optic sensors (DFOS) offer the exciting potential to significantly reduce the overall amount of spilled product before a leak is detected and localized. Such systems are not well represented by industrial standards or recommended procedures and as a result most industrial attempts to validate the technology have been research-oriented and whilst these have contributed greatly to the knowledge base they have never been aimed at a full validation of the technology. Additionally, the lack of test facilities that can support the significant scale needed for validation (> 500 m straight line run) have led to a paucity of attempts to provide a baseline validation of such sensing technology leading to a lack of certainty over performance claims within the industrial user base and no robust method of testing such claims. With a significant customer base of deployed systems, OptaSense have developed a reproducible technology validation approach using full scale, full flow, representative leaks at the CTDUT test facility in Brazil. We have used these tests to validate 15 lpm leaks, detected and classified via their negative pressure pulse in ∼10 seconds and larger 150 lpm leaks, detected by our four modes of leak detection in ∼1 minute. Valid automated detection of a negative pressure pulse (NPP) was observed down to 1 mm holes in the pipe — representing a leak rate of only 1.5 lpm. The use of the NPP is shown to be a compelling rapid detection method. However, care is needed in testing since the use of a valve opening to stimulate a pulse is shown to be significantly inferior to burst disks due to the increased valve-opening time giving rise to a reduced amplitude pressure pulse. The conventional external leak detection signals of Orifice Noise, Ground Strain and Temperature Change can all be shown to be replicated at the large-scale test facility by these means leading to the potential to establish a valid Probability of Detection for all approaches. With validation now possible, client verification on site has also been addressed with a two-step approach being developed that replicates the validation approach detailed above. Negative Pressure Pulses are used for stand-alone leak detection and can be safely stimulated via accessible valve sites and product release via a burst disc / valve and orifice combination. To stimulate the Multiple Mode behavior (excluding Negative Pressure Pulse) a controlled fluid release injection mechanism has been developed, which can be introduced at an appropriate offset from the pipeline (mirrored from fiber offset) at any desired location with the minimum of preparation. Ground probe deployment techniques have been designed to simulate a leak event at the appropriate location resulting in the similar external signals arising on the fiber. This paper presents the benefits of large-scale validation approaches to performance bound acoustic-based leak detection systems and presents established options for in-field verification on customer owned systems.

A better understanding of the sensitivity threshold of external leak detection systems can assist pipeline operators in predicting detection performance for a range of possible leak scenarios, thereby helping them to make more informed decisions regarding procurement and deployment of such systems. The analysis approach described herein was developed to characterize the leak detection sensitivity of select fiber optic cable-based systems that employ Distributed Acoustic Sensing (DAS). The detection sensitivity analysis consisted of two steps. The first step involved identifying a suitable release parameter capable of providing a defensible basis for defining detection sensitivity; the second step involved the application of logistic regression analysis to characterize detection sensitivity as a function of the chosen release parameter. The detection sensitivity analysis described herein provides a means by which to quantitatively determine the leak detection sensitivity threshold for each technology and sensor deployment position evaluated in a set of full-scale tests. The chosen sensitivity threshold measure was the release parameter value associated with release events having a 90% probability of being detected. Thresholds associated with a higher probability level of 95% were also established for comparison purposes. The calculated sensitivity thresholds can be interpreted to mean that release events associated with release parameter values above the sensitivity threshold have a very high likelihood (either 90 or 95%) of being detected.

A recent trend in the field of pipeline monitoring has been the utilisation of an optical fibre based distributed acoustic sensing (DAS) technology, for the purpose of security monitoring of buried pipelines [1–3]. The technology comprises an interrogator, connected to an optical fibre cable, which is interrogated to acquire coherent Rayleigh backscatter. Localised environmental vibrations may result in a proportional strain of the fibre. This strain results in a localised optical path length variation, resulting in a phase distortion in the measured signals. Application of signal processing techniques infer the characteristic of the originating stimulus, and thus identify and locate the source activity of interest. Activity may arise as a result of ground excavation, vehicular movement, or similar in the vicinity of the pipeline. Researchers are now studying the possibility of utilisng this technology for the purpose of pipeline leak detection monitoring [4]. This paper provides a review of one such programme of work. Results are presented for a permanent installation, where signatures relating to leaks were identified, and located in the resulting DAS data. Results are provided relating to liquid leaks, where product was emitted at a flow rate of 20.0l/minute and operational pressure 20.0bar.

The rehabilitation of damaged pipelines plays a critically-important role in maintaining the integrity management of pipeline systems. The repair techniques employed by pipeline operators typically include welded Type A and Type B sleeves, as well as composite repairs. Once repairs are made, operators must trust the integrity and soundness of the repairs based on various monitoring and inspection techniques; however, there are no current widely-accepted techniques for monitoring either the reinforcement or the pipe itself. A research program was conducted that involved the embedding of fiber optics in a steel sleeve and E-glass / epoxy composite repair systems. Measurements from the fiber optic sensors included temperature, hoop strain, and axial strain, which allowed engineers to monitor conditions in both the repair and the pipe sample. The implications of embedded technologies in pipeline repairs are far-reaching, including the ability to monitor not only the reinforcement itself, but also serve as a resource for monitoring pipeline activities including third party damage and land movement. This paper presents results from the test program, but also concepts for continued use of pipeline repair embedded technologies and their impact on the generation of large-scale data and enhancement of integrity management efforts.

Many pipelines are built in regions affected by harsh environmental conditions where changes in soil texture between winter and summer increase the likelihood of hazards. Pipeline routes also cross 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 effects. The analysis of scattering combined with a time domain technique allows the measurement of strain and temperature profiles. Temperature measurement is carried out to monitor 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 landslides. In some cases, actual pipe deformation must be monitored such as in the case of an 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 15 years of continuous development of pipeline geohazard risk monitoring with optical fiber distributed sensors from technology qualification and validation to its implementation in real cases as well as its successful continuous operation. Case studies presented include pipeline monitoring in Arctic and Siberian environment as well as in the Andes which illustrate how the technology is used and demonstrate proof of early detection and location of geohazard events such as erosion, landslide, settlement and pipe deformation.

The timely detection of small leaks from liquid pipelines poses a significant challenge for pipeline operations. One technology considered for continual monitoring is distributed temperature sensing (DTS), which utilizes a fiber-optic cable to provide distributed temperature measurements along a pipeline segment. This measurement technique allows for a high accuracy of temperature determination over long distances. Unexpected deviations in temperature at any given location can indicate various physical changes in the environment, including contact with a heated hydrocarbon due to a pipeline leak. The signals stemming from pipeline leaks may not be significantly greater than the noise in the DTS measurements, so care must be taken to configure the system in a manner that can detect small leaks while rejecting non-leak temperature anomalies. There are many factors that influence the frequency and intensity of the backscattered optical signal. This can result in noise in the fine-grained temperature sensing data. Thus, the DTS system must be tuned to the nominal temperature profile along the pipe segment. This customization allows for significant sensitivity and can utilize different leak detection thresholds at various locations based on normal temperature patterns. However, this segment-specific tuning can require a significant amount of resources and time. Additionally, this configuration exercise may have to be repeated as pipeline operating conditions change over time. Thus, there is a significant need and interest in advancing existing DTS processing techniques to enable the detection of leaks that today go undetected by DTS due to their signal response being too close to the noise floor and/or requiring significant resources to achieve positive results. This paper discusses the recent work focused on using machine learning (ML) techniques to detect leak signatures. Initial proof-of-concept results provide a more robust methodology for detecting leaks and allow for the detection of smaller leaks than are currently detectable by typical DTS systems, with low false alarm rates. A key use of ML approaches is that the system can “learn” about a given pipeline on its own without the need to utilize resources for pipeline segment-specific tuning. The potential to have a self-taught system is a powerful concept, and this paper discusses some key initial findings from applying ML-based techniques to optimize leak detection capabilities of an existing DTS system.

A significant portion of the global energy pipeline infrastructure is constructed with pipe materials manufactured using the Electric Resistance Weld (ERW) process. The longitudinal seam of these ERW pipelines may contain manufacturing flaws and anomalies that can grow over time through pressure cycle fatigue and result in a pipeline integrity failure. These flaws/anomalies can be present in both vintage pipe (generally pre-1970) manufactured using a low frequency ERW process and more modern pipe that is manufactured using a high frequency ERW process. ERW seam anomalies are challenging to detect, discriminate, and size with current In-Line Inspection and In-Ditch NDE inspection technologies, which is driving the industry to better understand current inspection industry performance and to develop new technologies for ERW seam anomaly inspection. Ultrasonic (UT) imaging using inverse wave field extrapolation (IWEX) is an emerging NDE technique that is being applied to improve discrimination and sizing of anomalies in pipelines. This paper will describe the IWEX development, the challenges related to seam weld integrity and assessment and SCC assessment, and results from studies to evaluate performance. Ultrasonic imaging is also compared to the current state-of-the-art techniques such as ultrasonic phased array (PA). A goal of the project is to produce images capable of discriminating cold welds, surface breaking hook cracks, non-surface breaking upturned fiber indications, poor trim, offset plate edges, and anomalies with fatigue cracking. The goal is to size all of the cracks in a SCC colony and produce a three-dimensional map of the area. In mapping these anomalies the sizing needs to be sufficiently accurate to qualify in-line inspection tools used for crack inspection.

In this paper, a methodology is presented to develop load factors for use in elastic-plastic assessments of pipelines and their components. The load factors are based on the pipe material properties and the ASME pipeline code’s design margin for the service and location of the pipeline installation [1, 2]. These codes are recognized by 49 CFR 192 and 195 [3, 4]. Minimum required load factors for internal pressure loads can be derived analytically based on design equations from the ASME B31 piping codes and minimum material requirements for API 5L line pipe [6]. Once the load factor is established for a particular case, the elastic-plastic methodology may be used in the Finite Element Analysis (FEA) of pipelines and related components. This methodology is particularly useful in the assessment of existing systems when linear elastic numerical analysis shows that local stresses may exceed the elastic design limits. Two case studies are presented showing analyses performed with Abaqus [5], a commercial, general purpose FEA software package. The first case study provides an assessment of a large diameter elbow where the stress on the outer fibers of the intrados exceeded the longitudinal stress limits from B31.8. The second case study examines an assessment of a tee connection where the stresses on the ID exceeded the yield strength of the component. In addition to the case studies, the paper also presents the results of a full-scale test that demonstrated what margin was present when the numerical calculations were based on specified minimum properties. This paper is not intended to revise or replace any provision of B31.4 and/or B31.8 [1, 2]. Instead, it provides the means for calculating load factors that can be used with an elastic-plastic analysis approach in a manner that provides the same design margins as the ASME B31 codes. The approach described in this paper is intended for use in the detailed FEA of pipelines and their associated components.

Leakage in oil and gas infrastructure, often cause significant financial losses, severe damage to the environment and raises public concern. In order to minimize the impact of spills, quick detection of a leak and a rapid response are needed. The systems currently employed to detect pipeline leakage range from simple visual checking to complex hardware and software systems such as mass balance, pressure point analysis, flow deviation, acoustic emission systems, and fibre-optic-based sensing technologies. These methods are useful, but there are certain limitations. The main drawback of the majority of these leak detection technologies is that they detect leakage indirectly, often unable to detect the leakage until the major spill. The preventive monitoring system and direct detection of hydrocarbon leakage are urgently needed to enable fast response and timely repairs with less deleterious effects. Research is being conducted for the development of a functional prototype and environmental testing of in-situ carbon nanotube (CNT) nanocomposite based sensors for hydrocarbon leakage detection. The CNT nanocomposite offers a unique approach to the direct hydrocarbon leakage detection in pipelines and aboveground storage tanks (ASTs). Expanding the study from the previous report of sensor characteristics under the optimal ambient condition, it was further investigated to identify the sensor performance under harsh conditions such as the underground (exposed to the soil) with compost and moisture, high pressure, changing temperature and long-term exposure to the outdoor environment. Investigation of the sensor behavior is studied, and a performance matrix is developed that accounts for the change in sensor response to various environmental conditions. Results showed that the proposed CNT nanocomposite sensor was applicable under given conditions with immediate responses while maintaining high sensitivity to the hydrocarbon leakage. Once a list of sensor detection specifications is defined, it is anticipated that the CNT sensor technology is applicable as part of a robust, reliable and accurate early detection system for the pipeline industry.

Fibre reinforced polymeric composites used in pressure retaining structures are seen as an attractive alternative to products made from conventional materials due to their corrosion resistance and high strength-to-weight ratio. The reluctance in adopting composite materials, however, is due to a limited understanding of the material behaviour under a variety of loading and environmental conditions, and lack of qualified design methodologies. It is the purpose of this paper to address fundamental and applied issues regarding their feasibility and current limitations in pipeline applications. A review of pertinent research results with respect to the local and global behaviour in composite pipes will be discussed.

Recent advances in PLC, SCADA and leak detection system technologies lead to the development of a highly integrated control system. Interconnected with fiber optic communication speeds (OC-1), this level of integration moves away from the historic model of stand-alone field controllers connected over low speed communication links to a centralized control center which, in turn, exchanges data from the host system to stand-alone leak detection processors. A new system design approach utilized familiar pipeline control elements such as PLC controllers and MODBUS communication protocols in combination with elements more typically associated with an office environment such as Windows NT servers, PC compatible computers, and Ethernet TCP/IP communications networks. These open-architecture components were used to fully develop, debug and test the SCADA system prior to system startup. The pipeline simulator is used as the centerpiece for this process to perform thorough operational validation of the system long before initial linefill. Once the various components were fully tested they were exported to the physical system in an operational state. The result is nearly seamless control systems supported by high data rates, high model speeds, common databases, and multi-channel communications. The increased level of integration has had dramatic impacts in leak detection, system safety, engineering development, operator training, and overall reliability of the control systems. The following paper presents a narrative overview of these new developments in the context of an implementation on Pacific Pipeline System (PPS). PPS is a recently constructed and commissioned 209 km (130 mile), 50.8 cm (20″) diameter, hot crude oil pipeline between the southern portion of California’s San Joaquin Valley and refineries in the Los Angeles basin. Following the Interstate 5 corridor over the “Grapevine”, Tejon Pass, Angeles National Forest and through heavily populated areas, this pipeline traverses some of the most environmentally and safety sensitive regions in the United States. The joint federal and state Environmental Impact Report / Environmental Impact Statement (EIR/EIS) set high hurdles for leak detection and control system performance. The historic control architecture and technologies were not adequate. This paper provides an overview of the environmental and physical constraints of the Pacific Pipeline System alignment, hydraulics, pumping and metering equipment, and block valve locations. It also discusses their impact on the design, programming and commissioning of a SCADA system meeting the requirements of the EIR/EIS. The paper then describes in more detail the fiber-optic communication system, control system architecture, SCADA system, leak detection models, simulator models and implementation methods, along with the engineering decisions leading to a comprehensive solution for the SCADA and leak detection requirements.

In laboratory testing of full-sized pipe subjected to combined axial load, internal pressure and bending, the normal failure mode consists of local buckling on the side of the maximum compressive fiber. If loading is continued beyond the initiation of buckling, and if the pipe is pressurized internally, the pipe retains its integrity while it develops a wrinkle in which very large deformations occur. Buried pipelines should behave in the same way. The paper presents the analyses carried out to assist in the interpretation of Geopig field evidence that, in September of 1997, a wrinkle existed on Slope 92 on the Norman-Wells Pipeline. A finite element analysis of a shell model of a segment of the pipe confirmed that the wrinkle should exist. A subsequent pipe dig uncovered the wrinkle which had a configuration remarkably similar to those observed in the laboratory and to the form predicted by the analysis. Supplementary geotechnical investigations, a review of operational procedures on the line, and additional testing to determine strains within wrinkles, are presented in companion papers elsewhere in this conference. These combined papers provide a thorough documentation relative to this most interesting case history.

Recent advances in SCADA and leak detection system technologies lead to higher scan rates and faster model speeds. As these model speeds increase and the inherent mathematical uncertainties in implicit method solutions are reduced, errors and uncertainties in measurement of the physical properties of the fluids transported by pipeline come to dominate the confidence calculations for computer generated leak alerts in the control center. The ability to collect more data must be supported by the need for better model data in order to achieve optimal leak detection system performance. This is particularly true when the products transported are non-homogeneous and have strong viscosity-vs-temperature relationships. These are characteristics of crude oils in California’s San Joaquin Valley where significant heating is required to pump these oils in an efficient manner. Proper characterization and correct mathematical expression of these physical properties in leak models has become critical. This paper presents these new developments in the context of an implementation of this new technology for the Pacific Pipeline System (PPS). PPS is a recently constructed and commissioned 209 km (130-mile), 50.8 cm (20″) diameter, insulated, hot crude oil pipeline between the southern portion of California’s San Joaquin Valley and refineries in the Los Angeles basin. Operational temperatures in this line vary from ambient to 82.2°C (180°F) with pressures ranging from 345 kPa (50 psi) to 11,720 kPa (1700 psi). Due to the unique geometry of the line, facilities along the route include pumping stations, metering stations and numerous “throttle-type” pressure reduction facilities. On PPS, a high-speed leak detection model is supported by a fiber optic (OC-1) communication backbone with data rate capacities in excess of 50 Megabits Per Second (MPS). Total scan times for the distributed communication system have been reduced to 1/4 second — each facility reports data to the SCADA host four times each second. A corresponding 1/4 second leak detection model cycle leads to selection of Methods of Characteristics segments on the order of 260 meters (850 feet). This resolution, in conjunction with the advanced instrumentation package of PPS, makes detection of very small leaks realizable. This paper starts with an overview of the system and combines a mix of the theoretical requirements imposed by the mathematical solutions with a practical description of the laboratory procedures and propagated experimental errors. The paper reviews temperature-related errors and uncertainties and their influence on leak detection performance.

A proprietary fibre optic sensing technology has been developed and is capable of simultaneously utilising an existing fibre optic communication cable as an integrity-testing sensing cable, thus providing continuous, real-time monitoring of the fibre cable and any structure near the cable (ie., ground, tunnels, ducts, pipes, buildings, equipment, vessels, etc.). With this system, simultaneous fibre optic communications and real-time vibration monitoring was demonstrated using a wavelength multiplexed fibre system for a channel bandwidth of 500 MHz over 18 km of standard singlemode fibre. Real-time vibration monitoring was also demonstrated using standard singlemode and multimode fibre over lengths of 28 km and 53 km, respectively. Trials of the system are currently underway in Australia and the first commercial field installation with this capability is to be completed in mid-1998 in Indonesia. This paper highlights the benefits and potential of this dual-capacity system and details results obtained to-date.

This paper describes R&D efforts and trends and possible application of new technologies to improve on pipeline construction and operations. The paper also identifies possible solutions for some operating concerns related to pipeline integrity and safety. Safety is defined as protection for humans, the environment and materials/equipment. As in other industries, the oil & gas business too is driven by events; a typical example is the current interest on Stress Corrosion Cracking (SCC). Accordingly, there are technical concerns related to the influence of SCC and aging on pipeline integrity and the consequent financial concerns regarding possible pipeline upgrading, derating, abandonment and possible retrieval. Potential new solutions include a proposed flexible tube (currently under development) made out of fibre glass composites. This patented innovation could reduce pipeline construction and operating costs. This tube could also eliminate some problems typically associated with metal corrosion. Also included is the application of Fibre Optic Sensor (FOS) technology to the monitoring and evaluation of pipeline integrity. FOS technology may be utilized to study SCC because of its high resolution, and its insensitivity to electro-magnetic interference, and its real time availability. This cost effective technology is currently utilized in the monitoring and evaluation of a variety of structures such as airplanes, engines, generators, bridges and along highways. Optical fibres have the ability to detect a wide range of physical, mechanical, chemical and biological parameters, as: • frequency • temperature • pressure • strain-stress • residual-strain • vibration • damage • impact • displacement • deformation • acoustic-emission • wear • electric-fields • acceleration • rotation • voltage • chemical-species • refractive-index • chemical-reactions • load • liquidlevels • cracking If a fibre optic cable acting as a sensor can be applied to a pipeline system in a practical manner, it may be possible to monitor the performance and conditions of a pipeline over its operating life.

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.

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.

The use of fibre optic based monitoring systems is becoming more common for new onshore pipelines. These systems are typically intended to provide leak detection and third party interference surveillance for long lengths of pipeline. Between 2006 and 2008 BP and OneSubsea™ developed the optical technology that provides the basis for a fibre optic pipeline monitoring system (presented in IPC2008-64549). Subsequently BP installed the system on its Khazzan Extended Well Test (EWT) pipeline system in a remote location in Oman. In addition to the originally designed leak detection and third party surveillance capability, operating experience gained by OneSubsea on a variety of pipeline projects has demonstrated the ability of the system to track the movement of pipeline pigs. The monitoring system interface has been upgraded to integrate this additional functionality. The paper describes the capabilities of the fibre optic monitoring system and through a case study illustrates the accuracy and operational benefits of the pig tracking capability.