Towards an Enhanced Telluric Compensation Methodology Chijioke Ukiwe & Shamus M c Donnell Hunter M c Donnell Pipelines Services Inc. Presented at AUCSC

Towards an Enhanced Telluric Towards an Enhanced Telluric Compensation MethodologyCompensation Methodology

Chijioke Ukiwe & Shamus MChijioke Ukiwe & Shamus MccDonnellDonnellHunter MHunter MccDonnell Pipelines Services Inc.Donnell Pipelines Services Inc.

Presented at AUCSC 2011 by Gord Parker, C.E.T., CP2Presented at AUCSC 2011 by Gord Parker, C.E.T., CP2Edmonton, Alberta, CanadaEdmonton, Alberta, Canada

CONGRESO SOBRE INTEGRIDAD EN INSTALACION DE GAS Y PETROLEO

This WorkThis Work• This paper is a progress report of an ongoing R&D This paper is a progress report of an ongoing R&D

project to develop an enhanced Telluric and AC project to develop an enhanced Telluric and AC interference compensation methodology.interference compensation methodology.– Research commissioned by Spectrum XLIResearch commissioned by Spectrum XLI– Partial funding from the Government of CanadaPartial funding from the Government of Canada

• This presentation was previously delivered at the This presentation was previously delivered at the NACE Northern AreaNACE Northern Area Western Conference.Western Conference.


Telluric Current

• A 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.


• 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.


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.


• How do telluric currents affect pipelines?How do telluric currents affect pipelines?

The sun emits

energy & Particles

Earth’s geo-

magnetic field

Voltage swings in CP systemsduring close interval survey CIS

Magnetic field

Induced electric currents on pipelines

Induced electric field

Source: space weather Canada


Telluric currents: economic importanceTelluric currents: economic importance

Test Post CSE

Pipeline

V Voltage

Time

Pipe-to-soil potential measurement

= Possibility of Corrosion

• Difficulty to pipeline integrity assessment – if uncorrected could result in incorrect interpretation and improper adjustment of CP system


• Telluric on pipe-to-soil potentials: practical exampleTelluric on pipe-to-soil potentials: practical example

5 Seconds grid2 Seconds CP

Interruption Cycle

40 Second Telluric Current Cycle

Low frequencyTemporal Voltage swing

= V at t for any pipeline location

Telluric current frequency varies; cycle times of a few seconds to minutes.


• AC Interference on pipe-to-soil potentialsAC Interference on pipe-to-soil potentials

Multiple Voltage swings superimposedon the pipe-to-soilPotential:

High frequency AC 50/60 Hz

Low Frequency telluric 1/40th Hz

4 second grid2 second CP Interruption Cycle


PIPELINE DISTANCE

A B C D

Tellu

ric

Mag

nit

ud

e

Regional Effects on pipeline structures on telluric variation:Valves, bends, rectifiers, anodes, insulating flanges

Telluric Potential Variation up to ~100 mV/Km at same moment

Telluric characteristics: Temporal Telluric characteristics: Temporal ANDAND Regional effects Regional effects

At the same moment in time

300mV 100mV

500mV400mV


Telluric characteristics: Temporal effectsTelluric characteristics: Temporal effects

At a given locationalong the pipeline,PSP changes with time

2. Space weather effects

20+ mV/sec

> 100mV / cycle telluric effect has been recorded!


What is “Telluric Compensation”?What is “Telluric Compensation”?

Voltage

Time

Time

VoltageExclusion of“Noise” on PSPData during CIS


Basis for Telluric CompensationBasis for Telluric Compensation

• Stationary PSP data (from stationaryStationary PSP data (from stationarydata logger (SDL)) summed over data logger (SDL)) summed over time yields “stable” time yields “stable” average PSPaverage PSP

• Comparable regional effects of Comparable regional effects of telluric on PSP within several kmstelluric on PSP within several kms

• SDL PSP data can be used to correctSDL PSP data can be used to correctfor any PSP variation in closefor any PSP variation in closeproximity proximity

PSP

PSP


Average PSP?Average PSP?

• Use statistics carefully, considering Use statistics carefully, considering duration of temporal effects, and size of duration of temporal effects, and size of data pool.data pool.

• Using data from a short time period, other Using data from a short time period, other than the actual survey period can result in than the actual survey period can result in error.error.

There are three kinds of lies: lies, damned lies, and statistics.

Benjamin Disraeli (1804 - 1881)


Current Field Practices for Telluric CompensationCurrent Field Practices for Telluric Compensation

1.1. Real-time telluric compensation; Real-time telluric compensation; based on stationary reference electrode placed at start of survey.based on stationary reference electrode placed at start of survey.

V+ -V

Telluric Pipe-to-soil potential variations are corrected real-time

SRE

Data Logger



1.1. Real-Time Compensation: pit-fallsReal-Time Compensation: pit-falls

- Unreliable representative average PSPUnreliable representative average PSP- Difference in Difference in regional telluric effectsregional telluric effects on pipe can render correction useless on pipe can render correction useless

Error in compensation increases away from Stationary electrode

A B

SRE Suppressed Telluric magnitude at B

High Telluric magnitude

at AX



2.2. Single Stationary Data Logger CompensationSingle Stationary Data Logger CompensationPost Processing For CompensationPost Processing For Compensation

- Reliable representative Reliable representative average PSP average PSP during surveyduring survey- Difference in Difference in regional telluric effectsregional telluric effects on pipe can on pipe can

render correction uselessrender correction uselessDifferences in regionaltelluric currents at A & Baffect correction method

A B

SRE + SDL

Suppression of Telluric magnitude at BX


A B

3. Multiple SDL Telluric Correction

C

Approximately linear telluric profile at anyGiven time, “t” within pipe section, AB



Multiple SDL Telluric Correction:Underlying Assumptions

• Based on Distributed Source Transmission Line (DSTL) Theory

• SDL placement spacing ~ 6 – 8 km

• Electrical continuity of telluric currents = uniformity of soil and pipeline characteristics

• Statistical average PSP is calculated from pool of readings that span entire survey period.


Multiple SDL Telluric Correction

SDL-A SDL-B


Multiple SDL Telluric CorrectionEnhancements

Field work Enhancements

Easier and fasterData

Post-processing

3-4 SDLsWaveform

Log

=

StrategicSDL

Positioning

And more reliable results!


Pipeline

A B C D

Tellu

ric

Mag

nit

ud

e

Enhanced Telluric Compensation: unique advantage ~ Enhanced Telluric Compensation: unique advantage ~

capturing FULL telluric variation trend along pipelinecapturing FULL telluric variation trend along pipeline


4 SDL Telluric Compensation Method: example

Telluric PSP Variation

-50

0

50

100

150

200

250

300

56440 56540 56640 56740 56840 56940 57040

Time (Sec.)

Te

llu

ric

Ma

gn

itu

de

(m

V)

MP: 496.1 MP: 500.0 MP: 502.3 MP: 503.5


PSPVariation(mV)

500.0 502.3496.1 503.5

SDL Placement (miles)

4 SDL Telluric Compensation Method:Practical safeguard against error!


Enhanced Telluric Compensation: Fast Interruption cycle Enhanced Telluric Compensation: Fast Interruption cycle

•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!

Telluric Variation can exceed50 mV per secondtimes cycle length = significant!


Multiple SDL Telluric Correction Enhancements:

(2) Post-processing

(a) Continuous waveform logging of the PSP (a) Continuous waveform logging of the PSP

Need to ensure the same readings are selected from both survey data and SDL – if different technologies used, errors can result


Multiple SDL Telluric Correction Enhancements:

(2) Post-processing

(b)(b) Simple moving average system on SDL data before telluricSimple moving average system on SDL data before telluric

compensationcompensation

Careful and thoroughChoice of each ON andOFF PSP data beforeTelluric correction usingSimple moving averagesOf telluric and highFrequency AC interferences


CI Survey Compensation

-1.6

-1.5

-1.4

-1.3

-1.2

-1.1

-1

-0.9

-0.8

-0.7

-0.6

26600+00 26605+00 26610+00 26615+00 26620+00 26625+00 26630+00 26635+00 26640+00 26645+00 26650+00

Station (ft)

Vo

lts

(C

uC

uS

O4

)

Survey Pol Comp Pol

Critical low Critical High

Multiple SDL Telluric Correction Enhancements: Final Post-processed data


… … Even further telluric enhancementsEven further telluric enhancements

• Recent advances in research holds promise for the use Recent advances in research holds promise for the use of telluric trends to forecast telluric magnitude over of telluric trends to forecast telluric magnitude over longer sections of pipelines = more strategic SDL longer sections of pipelines = more strategic SDL placements and time of survey.placements and time of survey.

• Ability to compensate for high frequency interference; Ability to compensate for high frequency interference; 50/60 Hz AC using high frequency stationary data 50/60 Hz AC using high frequency stationary data loggers.loggers.


ConclusionsConclusions

• The use of 3 ~ 4 Stationary data loggers to track telluric patternand ensure accurate compensation

• Fast cycles are preferred to avoid under/over-compensationto either ON or OFF pipe-to-soil potential data

• Continuous waveform logging can enhance data accuracy

• Advanced statistical approaches can enhance post-processingand hence, overall pipeline integrity


AcknowledgementAcknowledgement

The Authors are grateful to the National Research Council of Canada

for financial support through an Industrial Research Assistantship fund


Questions?Questions?

Documents

Towards an Enhanced Telluric Compensation Methodology Chijioke Ukiwe & Shamus M c Donnell Hunter M c Donnell Pipelines Services Inc. Presented at AUCSC