Real-time Subsea Pipeline Leak Monitoring using Fiber Optic Sensing Technology

Transcription

1 Real-time Subsea Pipeline Leak Monitoring using Fiber Optic Sensing Technology Prem Thodi, Ph.D., P.Eng., Senior Engineering Specialist INTECSEA Canada, WorleyParsons 12 th March 2015, Perth, Australia

2 Outline Introduction Real-time leak detection needs Existing leak detection technologies Internal / primary / CPM systems External / secondary systems Periodic leak testing systems Source: Fiber optic cable DTS and DAS Distributed leak sensing principle Key technology gaps Arctic pipeline leak detection JIP Summary and conclusions Source: 2

3 Introduction Demand for oil and gas will continue to drive deepwater and harsh environment subsea development Deepwater and harsh environment presents technical challenges Reliable operational strategies are needed to reduce risk Real-time pipeline leak detection is an important aspect of safe & economic hydrocarbon development 3

4 Subsea Pipeline Leakage Causes & Consequences Causes Structural degradation Corrosion, pitting, erosion, and SCC, HIC, fatigue cracking High bending strain due to differential settlement and ground movement Others Span, VIV, buckling, collapse Pipeline connections, valves, fittings Third party interventions Structural Degradation - Corrosion Consequences Safety Environmental Economical Negative reputation Structural Degradation Cracking 4

5 Real-time Pipeline Leak Detection Challenges Uncertain minimum thresholds of detection Remote performance monitoring and control Subsea equipment and power requirements Likelihood of false alarms Background noise reduction Installation and maintenance challenges Operational management using SCADA Uncertain operational reliability Source: NAXYS Monitor in Ormen Lange 5

6 Existing and Emerging Pipeline Leak Detection Technologies Leak Detection Technology Types Internal Based Systems Pressure/Flow Monitoring Acoustic Pressure Waves Balancing Methods Statistical Methods Real Time Transient Monitoring Extended RTTM External Based Systems Capacitance Methods Vapor Sensing Tubes Optical Camera Methods Bio Sensor Methods Fiber Optic Cable Methods Acoustic Methods Periodic Leak Testing Systems Intelligent Pigging Acoustic Pigging ROV/ AUV Inspection Underwater Gliders Subsea Towed Systems Remote Sensing Methods Bubble Emission Methods Fluorescent Methods PSL Switches Electrical Resistance 6 Annulus Monitoring in PIP

7 Internal Leak Detection Systems Utilize field sensor data to monitor pressure, temperature, density, flow rate, contamination, sonic velocity, product data at interfaces Mass balance system Pressure monitoring system Acoustic pressure wave monitoring Real-time transient monitoring (RTTM) Extended RTTM Source: Wave Alert System (Acoustic Systems Inc.) Infer commodity release by computation Install-able along with pipeline and SCADA Use acquired data to determine leakage Source: Atmos Pipe (ATMOS Intl.) 7

8 Mass Balance & Pressure Monitor Suitable for Mass Balance System Single Phase Oil transport pipelines Type of Instn. Permanent Permanent Type of Monitor Continuous Continuous Advantages Can detect large pipeline leaks Well established and matured technology Able to detect leaks in transient flow conditions less accurately Disadvantages Cannot detect small chronic leaks (i.e. sub 1% leaks) Prone to false alarms, reported poor performance in transient Not intended for use under lowflow or no-flow conditions Accurate multiphase leak detection is challenging Pressure Monitoring System Single Phase Oil / Multiphase flow pipelines Can detect large pipeline leaks Well established and matured technology Can be easily integrated into pipeline SCADA Cannot detect small chronic leaks (i.e. sub 1% leaks) Prone to false alarms, reported poor performance in transient Potentially requires intermediate monitoring points Multiphase flowline leak detection is challenging 8

9 Acoustic Monitoring & RTTM 9 Suitable for Acoustic Pressure Wave Monitoring Single Phase / Multiphase flow pipelines Type of Instn. Permanent Permanent Type of Monitor Continuous Continuous Advantages Quick leak detection Good for large leak detection Can detect location of leak Simplified sensor and software set-up with minimal calibration Disadvantages Background noise affects leak detection capability for small leak Difficult for multiphase flow Prone to false alarms No detection capability once the leak-noise misses the sensor Challenging for small leak on long pipeline (>40km) Real Time Transient Monitoring (RTTM) Single Phase Oil / Multiphase flow pipelines Very accurate in steady state Can detect small leaks (1%) Good for long oil pipelines RTTM Software algorithm are designed for leak location Extensive instrumentation is needed (flow, temp, pressure) Unsteady flow creates errors (or, false alarms) Calibration error could cause missed leaks or false alarms Sensitivity reduces with ultra long pipelines

10 Pros and Cons Internal LDS Internal leak detection systems can detect large leaks Easy installation and maintenance Limited ability to detect small, chronic leaks (sub 1% leak) Limited capability to locate leaks accurately Leak detection capability reduces with operations, like: Startup and shutdown Valve closures Transient flow Multiphase flow Prone to false alarms Cannot use under low-flow or non-flow conditions Source: Pressure Point Analysis (EFA Tech.) 10

11 External Leak Detection Systems Measures physical properties (temperature, acoustics, presence of oil particle, capacitance) around the pipelines Can be fixed on to pipelines or kept adjacent to pipelines Can be easily integrated into pipelines SCADA Hydrocarbon Vapor Sensors Fiber Optic Cable Sensors Vacuum Annulus Monitors (for PiP) Acoustic Sensors Capacitance Sensors Remote Sensors Source: Methane Vapor Sensor (Areva NP GmbH) Fluorescence & Optical Technologies 11

12 Vapor Sensing Tubes & Fiber Optic Sensing Suitable for Vapour Sensing Tubes Single Phase Oil / Multiphase flow pipelines and equipment Type of Instn Permanent Permanent Fiber Optic Leak Sensing Single Phase Oil / Multiphase flow pipelines Type of Monitor Continuous monitoring Continuous monitoring Advantages 30 years of service history, less unknowns Capable of detecting small chronic leaks (0.1m3/hr gas) Leak location accuracy is approx. 0.5% of total length Can work under low flow conditions Disadvantages Length and depth limitations are 15km and 15m Slow detection (i.e. 24hrs), additional protection required Handling, installation and maintenance are difficult Only detects leaks that evolve into sensing tube Can detect very small leaks accurately (sub 1% leaks) Can locate leaks very accurately No data link needed, no subsea power requirement, no electrical / EM interference, shutdown not required for calibration Can be used on long pipelines Multiple interrogator units are required for long (>50km) pipelines Increased installation cost for sensor and interrogator system Needs enhancement in technology readiness level

13 Pros and Cons External LDS Can detect small chronic (sub 1%) leaks Can locate small leaks accurately Can be used for long pipeline continuous leak monitoring Dependent on ocean diffusing material to the sensor Likelihood of false alarms Requirement of differential pressures Installation and maintenance difficulties Requirement of permanent installations Difficulty in quantifying size and rate of leak 13

14 Periodic Leak Detection Systems Not a continuous (i.e. 24x7) leak monitoring system Can be used for periodic leak testing, or when a leak is suspected Intelligent pigging Acoustic pigging ROV/AUV/overflight inspection Acoustic (active) technology Optical (camera) technology Underwater gliders Underwater towed systems Need support vessel for periodic ROV/AUV operation Source: COLMAR ALD mounted on ROV Source: NAXYS SALD (Left) and ALVD (Right) 14

15 Fiber Optic Cable Distributed Sensing Systems Distributed Temperature Sensing (DTS) Systems Oil leakage leads to local rise in temperature Gas leakage leads to local cooling FOC itself acts as the sensor and data link Raman band systems Brillouin band systems Distributed Acoustic Sensing (DAS) Systems Acts as a hydrophone Captures acoustic signature (i.e. vibration) generated by leaking fluid Noise separations No need to contact fluid with FOC sensors Rayleigh band systems 15

16 Principles of Operation When a short pulse of light is emitted, a proportion of the outgoing signal is scattered back to source due to impurities or defects in fiber microstructure Distributed Temperature Sensing Raman DTS System Based on intensity of backscattered signal Measures local change in temperature Brillouin DTS System Converts temperature effects on cable into frequency shifts of backscattered light Insensitive to the fiber attenuation changes over time and distance Distributed Acoustic Sensing Rayleigh DAS Measures minute strain effects on the sensor Strain is caused by acoustic vibrations Leak acoustic waves modulates the backscattered signal Cable pick up the acoustic signals, and when a distinguishable signature is detected, an alarm is triggered 16

17 OTDR Principle for Distributed Sensing Systems Light pulse Anti-Stokes Components Stokes Components Optical Source Detector Sensing fiber Backscattered signal Localization Principle of Optical Time Domain Reflectometer Optical Wave Spectrum (Raman, Brillouin, Rayleigh) ν ν -Ω ν Ω Stokes Component ν + Ω 17 Ω Anti-Stokes Component

18 FOC Distributed Sensing Leak Detection System Components Typical DTS Cable Typical DAS Cable 1. HDPE outer sheath 2. Galfan high strength steel wire 3. Gel-filled metal tube SS 316L 4. Bend insensitive optical fibers 1. PA Outer sheath 2. Stainless steel 316 L metal tube 3. Inner interlocking system 4. Multilayer acoustic coupling layer 5. Bend insensitive optical fiber 18

19 Typical Optical Budget Requirements Optical Loss Calculations for Distributed Temperature Sensing (DTS) Systems Deepwater Pipeline Losses Optical Loss per Splice 0.10 db/splice No of splices 3 Splice Loss 0.3 Optical Loss per No of Connector 0.50 db/connector 2 Connector connecters Loss 1.0 Fiber Loss per km 0.36 db/km Propagation length (km) 80 Fiber Loss 28.8 Safety Margin 3.00 db Total Loss (db) 33.1 Optical Loss Calculations for Distributed Acoustic Sensing (DAS) Systems Deepwater Pipeline Losses Optical Loss per Splice 0.1 db/splice No of splices 3 Splice Loss 0.3 Optical Loss per No of Connector 0.3 db/connector 4 Connector connecters Loss 1.2 Fiber Loss per km 0.2 db/km Propagation length (km) 80 Fiber Loss 16.0 Safety Margin 3.0 db Total Loss (db)

20 Technology Status (TRL/TRC) Technology Readiness Levels (TRL) Technology Readiness Levels (TRL) Major Components Interrogator Unit Processing Unit Control Unit Sensing FOC DTS & DAS Technology Risk Categorization (TRC) Technology Readiness Level Key Points (API RP 17N) DAS DTS 3 3 Technology Risk Categorization (TRC) Risk Category Key Points Reliability Technology Architecture/ Config. Concept proven, prototype tested in lab for performance, functionality, reliability. Preproduction system environmental (i.e. deepwater) test not yet performed. Operating Environment Org. Scale/ Complexity High (B) High (B) High (B) Very High (A) High (B) False Alarms MTBF Installability Long Length Installability New Application Deepwater LDS Uncertainty Relatively New Team Overall Risk Very High (A) 20

21 FOC Positioning for Deepwater Pipeline Leak Detection 21 Assumptions: Positioning is based on damage prevention during installation as well as increased detectability regardless of leak location and current direction FOC sensor needs to be close to the leakage for effective leak detection

22 Fiber Optic Cable Installation & Maintenance Challenges Need to pass over lay vessel and stinger roller supports S-Lay Lay barge reconfiguration requirements Limitations of cable splices offshore Optimum location or orientation of DTS and DAS cables DTS cable need to be in close proximity to the pipeline, DAS can be away Reel Lay Cable repair is challenging, so need to consider providing redundancy Installation and maintenance of subsea (marinized) repeaters 22

23 Technology Gaps Minimum thresholds of detection Inadequate technology status False alarm reduction Reliability of systems Long pipeline application Sensor positioning/orientation Lack of deepwater experience Interrogator installation and repair Leak size quantification difficulty 23

24 R&D Initiatives on FOC Testing Overall aim of the JIP is to test detectability, determine minimum thresholds of detection (i.e. minimum leak rate & response time), enhance technology readiness level, simulate cold-region, deepwater environmental testing, and identify false alarm rate Phase I Designing, costing, scheduling and execution planning to establish the basis and boundary of the testing program Phase II Large scale field testing in a simulated environment in St. John s, Newfoundland and Labrador, Canada 24 General Test Setup

25 R&D Initiatives on FOC Testing Completed JIP Phase I Tasks Novelties Definition of physical test Long cable (up to 40 km) Test facility selection Low ambient temperature (4 C) FOC DTS / DAS selection Large test tank (20 x 10 x 3m) Optimal sensor positioning Integrated (DTS/DAS) testing Testbed geotechnical evaluation Small leak detection testing Test procedure development Cost and schedule development Test HSE management plan Phase II Large scale field testing (proposed) 25

26 Summary & Conclusions Pipelines are designed to safely transport produced hydrocarbons Pipeline leaks can have severe safety, economical and environmental consequences Existing leak detection technologies Internal / Primary / CPM systems External / Secondary systems Periodic Leak Testing systems FOC DTS and DAS technologies Operating principles Optical budget requirements Installation and maintenance Technology status (TRL/TRC) Key technology gaps are identified R&D initiatives to close the specific gaps 26

27 Questions? Contacts Prem Thodi: Mike Paulin:

28 DISCLAIMER This presentation has been prepared by a representative of WorleyParsons. The presentation contains the professional and personal opinions of the presenter, which are given in good faith. As such, opinions presented herein may not always necessarily reflect the position of WorleyParsons as a whole, its officers or executive. Any forward-looking statements included in this presentation will involve subjective judgment and analysis and are subject to uncertainties, risks and contingencies many of which are outside the control of, and may be unknown to, WorleyParsons. WorleyParsons and all associated entities and representatives make no representation or warranty as to the accuracy, reliability or completeness of information in this document and do not take responsibility for updating any information or correcting any error or omission that may become apparent after this document has been issued. To the extent permitted by law, WorleyParsons and its officers, employees, related bodies and agents disclaim all liability direct, indirect or consequential (and whether or not arising out of the negligence, default or lack of care of WorleyParsons and/or any of its agents) for any loss or damage suffered by a recipient or other persons arising out of, or in connection with, any use or reliance on this presentation or information.