Presentation on theme: "Towards an Enhanced Telluric Compensation Methodology"— Presentation transcript:
1 Towards an Enhanced Telluric Compensation Methodology Chijioke Ukiwe & Shamus McDonnellHunter McDonnell Pipelines Services Inc.Presented at AUCSC 2011 by Gord Parker, C.E.T., CP2Edmonton, Alberta, Canada
2 This WorkThis paper is a progress report of an ongoing R&D project to develop an enhanced Telluric and AC interference compensation methodology.Research commissioned by Spectrum XLIPartial funding from the Government of CanadaThis presentation was previously delivered at the NACE Northern Area Western Conference.
3 Telluric CurrentA telluric current (from Latin tellūs, "earth") is an electric current which moves underground or through the sea.The currents are extremely low frequency and travel over large areas at or near the surface of Earth.Telluric currents are also observed in the Earth's crust and mantle.
4 Telluric currents are primarily induced by changes in the outer part of the Earth's magnetic field, usually caused by interactions between the solar wind and the magnetosphere or solar radiation effects on the ionosphere.
5 Some Telluric Current Facts The magnitude varies, but can be in the order of 100's to 1000's of Amperes.Local variations in the conductivity of the Earth's crust affect the density of these currents as they follow the path of least resistance. This effect can be used to detect the presence of low-conductivity ore bodies beneath the crust in geological surveys.Along with the currents induced in the Earth's crust, any man-made conducting objects on or beneath the Earth's surface will also have large currents induced in them. This can cause power grid systems to trip from the overload.High sun-spot activities can buffet the Earth's magnetic field, causing fluctuations which in turn induces telluric currents on earth conductors, increasing the likelihood of such interruptions.
6 How do telluric currents affect pipelines? Magnetic fieldEarth’s geo-magnetic fieldThe sun emits energy & ParticlesVoltage swings in CP systemsduring close interval survey CISInduced electric fieldThe DSTL theory proposes that telluric currents are produced when an induced electric field, caused by changing magnetic field outside the earth, drives an electric charge along the pipeline, which causes a movement of charges from end and a build-up at the other.Induced electric currents on pipelinesSource: space weather Canada
7 V Telluric currents: economic importance = Possibility of Corrosion VoltageTimeVTest PostCSEDifficulty to pipeline integrity assessment – if uncorrected could result in incorrect interpretation and improper adjustment of CP systemPipeline= Possibility of CorrosionPipe-to-soil potential measurement
8 Telluric on pipe-to-soil potentials: practical example 5 Seconds grid2 Seconds CP Interruption CycleSecond Telluric Current CycleLow frequencyTemporalVoltage swing= DV at t forany pipelinelocationTelluric current frequency varies; cycle times of a few seconds to minutes.
9 AC Interference on pipe-to-soil potentials Multiple Voltage swings superimposedon the pipe-to-soilPotential:High frequency AC50/60 HzLow Frequency telluric 1/40th Hz4 second grid2 second CP Interruption Cycle
10 Telluric characteristics: Temporal AND Regional effects At the same moment in timeTelluric Magnitude500mV400mV300mV100mVPIPELINE DISTANCECDABRegional Effects on pipeline structures on telluric variation:Valves, bends, rectifiers, anodes, insulating flangesTelluric Potential Variation up to ~100 mV/Km at same moment
11 Telluric characteristics: Temporal effects 2. Space weather effectsAt a given locationalong the pipeline,PSP changes with time20+ mV/sec> 100mV / cycle telluric effect has been recorded!
12 What is “Telluric Compensation”? VoltageTimeTimeVoltageExclusion of“Noise” on PSPData during CIS
13 Basis for Telluric Compensation Stationary PSP data (from stationarydata logger (SDL)) summed overtime yields “stable” average PSPComparable regional effects oftelluric on PSP within several kmsSDL PSP data can be used to correctfor any PSP variation in closeproximityPSPPSP
14 Average PSP?Use statistics carefully, considering duration of temporal effects, and size of data pool.Using data from a short time period, other than the actual survey period can result in error.There are three kinds of lies: lies, damned lies, and statistics.Benjamin Disraeli ( )
15 + - Current Field Practices for Telluric Compensation Real-time telluric compensation; based on stationary reference electrode placed at start of survey.Data Logger+-VVSRETelluric Pipe-to-soil potential variations are corrected real-time
16 X Current Field Practices for Telluric Compensation 1. Real-Time Compensation: pit-fallsUnreliable representative average PSPDifference in regional telluric effects on pipe can render correction uselessXHigh Telluric magnitude at AError in compensation increases away from Stationary electrodeSRESuppressed Telluric magnitude at BAB
17 X Current Field Practices for Telluric Compensation Single Stationary Data Logger CompensationPost Processing For CompensationReliable representative average PSP during surveyDifference in regional telluric effects on pipe can render correction uselessXDifferences in regionaltelluric currents at A & Baffect correction methodABSRE + SDLSuppression of Telluric magnitude at B
18 3. Multiple SDL Telluric Correction Current Field Practices for Telluric Compensation3. Multiple SDL Telluric CorrectionABCApproximately linear telluric profile at anyGiven time, “t” within pipe section, AB
19 Multiple SDL Telluric Correction: Underlying Assumptions Based on Distributed Source Transmission Line(DSTL) TheorySDL placement spacing ~ 6 – 8 kmElectrical continuity of telluric currents =uniformity of soil and pipeline characteristicsStatistical average PSP is calculated from pool of readings that span entire survey period.
25 Enhanced Telluric Compensation: Fast Interruption cycle Telluric Variation can exceed50 mV per secondtimes cycle length = significant!Use of Fast InterruptionCycle of about ~1 second = ON:OFF (~3:1) = <50mV per cycle (simple 1 potential / cycle correction)Longer cycle makes it necessary for independent Telluric correction for ON and Instant Off PSP; different magnitude at start of cycle and end of cycle!
26 Multiple SDL Telluric Correction Enhancements: (2) Post-processing(a) Continuous waveform logging of the PSPNeed to ensure the same readings are selected from both survey data and SDL – if different technologies used, errors can result
27 Multiple SDL Telluric Correction Enhancements: (2) Post-processing(b) Simple moving average system on SDL data before telluriccompensationCareful and thoroughChoice of each ON andOFF PSP data beforeTelluric correction usingSimple moving averagesOf telluric and highFrequency AC interferences
28 Multiple SDL Telluric Correction Enhancements: Final Post-processed data
29 … Even further telluric enhancements Recent advances in research holds promise for the use of telluric trends to forecast telluric magnitude over longer sections of pipelines = more strategic SDL placements and time of survey.Ability to compensate for high frequency interference; 50/60 Hz AC using high frequency stationary data loggers.
30 ConclusionsThe use of 3 ~ 4 Stationary data loggers to track telluric patternand ensure accurate compensationFast cycles are preferred to avoid under/over-compensationto either ON or OFF pipe-to-soil potential dataContinuous waveform logging can enhance data accuracyAdvanced statistical approaches can enhance post-processingand hence, overall pipeline integrity
31 The Authors are grateful to the National Research Council of Canada AcknowledgementThe Authors are grateful to theNational Research Council of Canadafor financial support through an IndustrialResearch Assistantship fund