Tracerco Insight V1 E2 4Qtr 08

The separation process is a fundamentalpart of all hydrocarbon production. The ideal for operators is to produce oilfree from gas and water, remove all liquidsfrom gas, and discharge produced waterthat is within environmental limits.

The application of a TRACERCODiagnosticTM Separator Study allows thedetection of process issues in separator andwater treatment systems in real time. Usingdata collected, solutions can be found tobetter control separation and prevent harmful discharge. This article describeshow this technology can be used to identifyproblems that occur within separation systems including:

• Scaling• Oil in water• Damage to vessel internals • Blockages in perforated plates• Flow distribution• Residence times• Slugging• Emulsions• Foam• Deposit build-up

Scale ProblemsProduced water can be very rich in salts,

in fact the dissolved solids content in pro-duced water is usually much greater thanthat of normal sea water. Salts are initiallydissolved in the water present in a reservoirbut as conditions change when the water isproduced, the salts may form solids anddeposit as scale. This can reduce pipediameters, plug vessels and equipment thatin turn can lead to diminished separationefficiency.

Regular density measurements acrosspipe work where scaling may be an issue

allows a quantification of the amount ofscale that is building up, allowing timelyinterventions to be performed by a special-ist cleaning company prior to a completeblockage. As scale is more dense than production fluids, its presence within a pipecan be readily detected using aTRACERCO DiagnosticsTM Pipe Scan.

Figure 1 illustrates results from a scanused to detect a blockage within a 6" produced water pipe. Measurements weretaken every 10 inches along the blocked

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INSIDE THIS ISSUE…

Oil & Gas Separator Optimization: Real Time Process Characterization .............1

Keeping Track...............................................4

TRACERCO Diagnostics™ Scan

Measurement Position on Pipe

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Figure 1 – Results from a scan of a 6" produced water pipe.

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Oil & Gas Separator Optimization: Real Time ProcessCharacterization By Dan Benson and Paul Hewitt

line and a density versus dis-tance plot was created.Knowing the approximate den-sity of the scale and knowingthe density of material thatshould have been present within the pipe, any reductionin signal was due to scale build-up. Using this data thethickness of scale could bedetermined at each position andthe blockage accurately located.

Fluid Distribution, ResidenceTimes and Equipment BlockageMeasurement

Specialist radiotracer studieson separators can be used todetect problems such as oil inwater, water in oil, gasundercutting, or liquid carryover.It can also detect the affect ofblockages in perforated plates,flow distribution and accuratelymeasure individual phaseresidence times.

The basic principle of a tracerinvestigation is to label a sub-stance or phase and then followit through a system. Looking attracer studies from a problemsolving point of view, if prob-lems of fluid transport can bedescribed in terms of ‘When?’,‘Where to?’, and ‘How Much?’,then they can be solved bymeans of tracer techniques.

The basic requirements of atracer include:

• Identical behavior to thematerial under investiga-tion

• Unambiguous detection atlow concentrations

• No affect on the processunder investigation

• Minimal residual concen-tration in the product.

The criteria can be met by theuse of short-lived radioisotopetracers and by careful selectionof the most appropriate tracerfor a particular application. Thetechnology requires a numberof sensitive radiation detectorsto be located on the walls aswell as the inlet and outlet ofthe vessel under investigation.A radiotracer is injected intothe process and if the materialflows past a detector position itwill register as a response ver-sus time. Analysis of eachdetector response providesinformation on flow distribu-tion and timing allowing flowdynamics within the vessel tobe determined.

Figure 2 shows the position ofdetectors during a tracer studyon a gravity separator. A gas,oil or water radiotracer isinjected upstream of the vesselto allow adequate mixing withall phases. The first detector(D1) is positioned just after theinjection point and provides

information on the shape of theinjected radiotracer pulse. Thenext four detectors (D2) arepositioned as a ring around theinlet pipe. By comparing theradiation intensity against timefor each of the detectors, flowdistribution at the inlet can bestudied and maldistributiondetected. These also act as azero point for residence timewithin the vessel. The nextring of detectors (D3) istypically focused around thelower parts of the vesseloutside of any inlet devices.Assuming a separator withinlet cyclones these detectorswill show any maldistributionor gas undercutting fromwithin the inlet equipment.

More detector rings (D4)may be positioned close toseparator internals such as per-forated plates. Comparing datafrom each of these will giveinformation about partial or full

blockage of the plates indicatedby maldistribution. In addition,comparing results from detec-tors in one ring along the vessellength with results from otherdetector rings, information isprovided showing how a specificphase moves laterally throughthe vessel. The detectors at thegas outlet (D5) give flow distribution and vapor residencetime in the separator. They alsoprovide information on liquidcarry over following liquid tracer injection. Detectorsaround the oil and water outlets(D6 & D7) detect residencetime of the specific phase, oil in water underflow, water in oil overflow as well as gasundercutting.

Figure 3 shows examples ofdetector responses from a liquidtracer study on a vertical two-phase separation vessel. The

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Oil & Gas Separator(Continued from page 1)

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Gas Outlet

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Figure 3 – Measurement results from a vertical two-phase separator.

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Figure 4 – Measurement of liquid distribution in a vertical separator.

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Continued on page 3Figure 2 – Typical detector positions in a gravity separator.

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time between liquid tracerinjection and detector responseat the outlets provides residencetime in the process vessel.Additionally, the shape andduration of the signal at the out-lets gives information aboutmixing in the vessel. Finally,the presence of tracer responseat the gas outlet detector allowsmeasurement of liquid carryover from the vessel. Figure 4shows the response from aninlet detector and four detectorspositioned at equal distancesaround the vessel at the sameelevation. Results reveal unevenflow distribution within the ves-sel with increased tracer andhence liquid flow in the westernquadrant. In addition, thesouthern quadrant reveals lessliquid flow at a lower velocityindicating poor distribution or apotential blockage in this sec-tion of the vessel.

Damage to vessel internalsDamage to vessel internals,

especially an inlet device, canhave a serious impact on theability of a vessel to separateoil, water and gas. ATRACERCO Diagnostics™Scan can be used to check themechanical integrity of vesselinternals. If the process is on-stream, measurements arelimited to the vapor spaceabove liquids. However, if thevessel is drained, virtuallyanything can be measured.

Figure 5 shows examples ofscan lines and detectorpositions used to check that allinlet cyclones in a separator arein place. Solid structuresbetween source and detectorattenuate the signal and theamount detected gives anestimate of how much steelthere is across the measurementpath. In recording the data, thetransmitted intensity, expressedin detector count rate is plottedon a logarithmic scale so thatthe transmission characteristicfaithfully reflects the densityprofile of the scan line. Thedetected intensities provideinformation about the integrityof the internals. This infor-mation can be used to explainseparation inefficiencies andhelp plan necessary shutdownrepairs.

Rag Layer (emulsion) andDeposit Build-Up

TRACERCO Diagnostics™Scanning technology can alsobe used to detect deposits andvapor profiles in pipelines, thepresence and extent of a raglayer between oil and waterand solid deposits in separators.

Figure 6 shows typicalinterface profiles at differentlateral positions along aseparator vessel. The extent ofrag layer can be measured bythe gradient of the responsechange between oil and water.Typical results show oil-waterinterface quality improvementas measurements are madeaway from the inlet devicemoving towards the weir or

outlet bucket. The technologycan be used very effectively inemulsion breaker chemicaltrials to determine the best typeand concentration to use in aparticular vessel. In turn, thiscan lead to significant costsavings as well as reduce theenvironmental impact of excesschemical use.

Solid build-up in a vessel isof importance as any significantreduction in the free volume ofa vessel will lead to a reductionin residence time leading to

reduced separation efficiency.Neutron scanning technologyholds many advantages overinfrared with measurementbeing made without theremoval of insulation and is notaffected by external heatsources on the vessel surface.

Detection of Vapor and LiquidSlugging

Slugging can cause majorupsets and process instabilitiesresulting in production losses aswell as an increase in harmfuldischarges. In some situationsthe presence of slugging candamage process equipment. Ifslugging is found to be presentwithin a process system it isimportant to understand itscharacteristics. This may allowchanges to be made that willreduce or eliminate its presenceand the detrimental affects onprocess hardware.


Figure 5 – Cross sections of inlet cyclones in a separator vessel. Examples of source, detector positions andscan lines are shown.

Front viewSource Source

Detector

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Side view Top view withexamples of scan lines

Figure 6 – Shows interface profiles at various positions in an MP separator vessel.

Scanning distances from inlet tan-lineLine A 2750mm Line D 11750mmLine B 5750mm Line E 21000mmLine C 8750mm Line F 22400mm

Normal Liquid Level 2170 mmNormal Interface Level 1160 mm

Line F (After Weir)Line ELine DLine CLine BLine A

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Continued on back page


Keeping TrackBy Lee Robins, Business Development Manager, Tracerco Billingham, UKRecently published in World Pipelines October 2008

Companies are fast realizingthe importance of fully under-standing what makes a success-ful pigging campaign. Tracercois experiencing an ever-growingnumber of inquiries about itsflow assurance study and pigtracking service, as clients real-ize the benefits of optimizingtheir cleaning regimes, and thepeace of mind gained whiletracking critical pipeline pigs.Tracerco has completed pro-jects worldwide, includingchallenging environments suchas the Arctic Circle and in thedeep waters of the Gulf ofMexico.

Why pig a pipeline?Introducing a foreign object

into any pipeline carries a riskof blockage and it is importantto understand why pipelines arepigged to determine the mostsuitable detection methods.

Pipeline pigging is carriedout for the following reasons:

• To clean pipelines beforeuse.

• To fill lines for hydrostatictesting, dewatering followinghydrostatic testing, dryingand purging operations.

• To periodically remove wax,dirt and water from thepipeline.

• To sweep liquids from gaspipelines.

• To separate products toreduce the amount of mixingbetween different types ofcrude oil or refined products.

• To control liquids in apipeline, including twophase pipelines.

• To inspect pipelines fordefects such as dents, buck-les or corrosion.

• To isolate sections of apipeline for tie-in or repairpurposes.

In critical applications whereaccuracy, reliability and confi-dence are most important, iso-topes have scored particularlywell in market studies. The fol-lowing applications are themost crucial and are more read-ily suitable for isotope tracking:

Any application after firstinstallation, such as flooding,cleaning and gauging – In thisinstance, installation may havecaused the pipeline to buckle,or an engineering defect maycause the pig to get stuck andany delays will result in higherproject costs.

Any inspection campaignusing intelligent pigs – Thesepigs can be very long, in orderto accommodate all of theinspection tooling required.Thus, they have a higher poten-tial to lodge in the pipelinewhile negotiating bends oroverhang pig trap valves.

The first pig run - After anypipeline modification work, asdebris may remain or an engi-neering defect may haveoccurred.

Whenever a pipeline isola-tion tool is being used – andaccurate positioning is criticaland/or long signal life isrequired to reliably track thetool after de-isolation.

Other factors that are importantwhen assessing the criticalityof a pig run include:• Whether a pipeline has ever

been inspected before. Thisis due to an unknown vol-ume of deposit that may be

present in the pipeline.• Pipelines that, due to the

nature of the product flow-ing, have the potential forhydrates to form. This willcause flow blockages andrestrict the motive force inthe pipeline to drive the pigthrough.

• Concern over a valve andwhether it is fully open toallow the passage of a pig.

• How accurately a pig needs

to be located.• The time in which a pig

must be able to be located.For instance, some pipelinemodification work can takeup to a year. Thus, knowingwhere the pipeline pig isafter that time is highlyadvantageous.

The ultimate objective ofevery pig run is to complete thetask required and return thepipeline to its orginal operatingcondition in the shortest timepossible. A stuck pig can haveextremely costly implications.Therefore, it is important todetermine with confidence the

likely success of any piggingcampaign, have a contingencyshould the pipeline pig becomestuck (including accurate loca-tion), and monitor the effective-ness of any campaign.

Pig tracking…There are many factors that

can affect the outcome of a pig-ging campaign and it’s alwaysgood for an operator to knowthe location of the pigging toolsinside the pipeline.

Choosing a radioisotopetracking service

Isotopes are mainly chosenfor critical applications. Asmall, low powered radioactivesource is attached to the pigbody prior to being launched,which sends a constant gamma-ray signal that can be detectedon the outside of the pipeline.This solution has a number ofbenefits:Detection time

As an isotope constantlyemits a naturally occurring sig-nal, it means that there are noconcerns regarding battery life.So, should an operator be usinga plug to isolate a line and thedownstream modification workdoes not go to plan, there willbe no concern over having to

Continued on page 5

Isotope tracking has been found to be one ofthe most reliable, accurate and confidencegiving solutions in critical applications.

Figure 9 – This photograph shows the location of stuck pig due to engineering modification not relayed to pigging contractor.


locate the pig within a certaintime period. Therefore, pigs cannow be launched from subsealaunchers, lying dormant for anumber of months prior to useagain, using isotopes. This willeliminate concern about detectionafter launch.

Accurate positioningDue to the highly collimated

radiation beam, a pig’s locationcan be accurately located. Thus,in terms of a long tool, it mayonly just fit in a pig receiver.Therefore, knowing the exactlocation of the back of the pigwill allow an operator to close thetrap valve with confidence thatdamage will not occur to thevalve or the intelligent pig.

Reducing component partsWhenever systems are consid-

ered, those with fewer componentparts are more reliable, so reduc-ing the need for batteries by usinga naturally occurring signalincreases reliability.

Other benefits of using iso-topes for pig tracking include:

• The pipe diameter does notmatter. Isotopes can be usedto track pigs in small umbili-cal lines and the largesttransport lines (i.e., fromseveral millimeters to severalmetres in diameter).

• Thick wall pipelines orweight-coated lines do notpresent a problem for thetransmission of the signal.

• The contents of the line areirrelevant to the passage ofthe signal; gas, liquid or mul-tiphase.

• Can be used for pipe-in-pipepig tracking. Other technolo-gies are seriously affected bythis type of application.

• Can be attached to any typeof pig or pipeline tool on themarket with no effect on theperformance of the pig.Batteries used in other tech-nologies can be extremelycumbersome.

• The signal can be detected atall times irrespective ofwhether the pipeline is sub-sea or on land. So, should asubsea pipeline comeonshore at a terminal, theisotope is always detectable.

• Multiple pigs can be trackedand/or located. Using differ-ences in the amount of radia-tion emitted or different iso-topes with different ‘signa-tures’, each pig can be givena unique identifier.

Flow assurance studiesConsidering an example,

assuming a pig is run in a 24 in.pipeline 100 miles long andremoves 0.016 in. of wax materi-al from the wall of the pipeline.After 100 miles, a plug approxi-mately 1450 ft. long would form.Therefore, it’s important to definehow much deposit is located in aline. Tracerco’s involvement withmany pigging campaigns startswell before the launch of the firstpig. Often, clients have applica-tions where a pipeline pig hasnever been run through a line; orwell conditions have changedwith time, meaning conditionsare occurring that can affect theflow properties of the pipeline,such as wax, hydrate, sand orscale. As part of its PrecisionDiagnostics portfolio, Tracercooffers its flow assurance studytechnique that can be used toensure the effective flow of oiland gas through an oil and gasprocessing facility or pipeline.

Many operators are extremelycautious when it comes to tackling pipelines that havenever been pigged, as there is thepotential for tools to become

stuck due to unknown depositamounts. Tracer techniques, sim-ilar to a barium meal used inmedical technology, can be usedto determine deposit location.The tracer injection techniquerequires the injection of a smallamount (typically no more than50 ml) of low activity radiotracerinto the line in the form of asharp liquid pulse, enabling thefluid velocity between externallymounted radiation detector log-gers to be measured to betterthan 0.1% accuracy. For aknown flowrate, a velocitybetween points can be derived.However, should deposits beencountered, this will cause thevelocity of the tracer pulse toincrease. Comparing this to thepipeline flowrate for the durationof the test enables the amount ofdeposit between successivedetectors to be calculated. Thetracer used is designed to flowwith the particular materialthrough the system. Sensitiveradiation detectors are placed onthe outside surface of the pipe(detectors are depth rated to3000 m) and detect the unsealedtracer as it passes each specificdetector position. These mea-surements can be used to direct-ly measure fluid velocity,flowrate, phase distribution and

deposit inventory.Running a flow assurance

study before and after a pigcleaning campaign will allow anoperator to determine the effec-tiveness of the pigging run. Thishas significant benefits:

• Many intelligent pig runs faildue to the cleanliness of thepipeline after cleaning. Aflow study will determinewhether the line has reachedan acceptable standard forthe intelligent pig run tobegin, reducing the likeli-hood of an expensive re-runof the intelligent pig.

• Pig cleaning campaigns canbe optimized. Reducing runsto the minimum necessarywill have the following bene-fits: minimize cost by reduc-ing the number of times pig-ging specialists need to visita platform; limiting thepotential for environmentalincidents by reducing thenumber of containmentbreaks that take place; andan increase in safety as pig-ging operations can be attrib-uted to two explosions in thelast decade.

• Pipeline dosing chemicalscan be optimized, thus, hav-ing significant cost and envi-ronmental benefits.

Figure 10 – Injection of tracer and detection points.

Figure 11 – Passage of tracer past detector points.

Keeping Track(Continued from page 4)

Figure 7 shows the set-up of aTRACERCO Diagnostics™Slug Monitoring system. It consists of two non-intrusivedensitometers positioned at aknown distance apart on pipework. The measurement of den-sity change in the pipe overtime at each position and analy-sis of the shape of the densitychange allows a slug to be fullycharacterized with key informa-tion such as velocity, size, andfrequency. In addition, the esti-mated arrival time at a separatorcan be calculated so remedial

action can be taken to avoiddamage or upset.

A typical slugging trend is

shown in Figure 8, which showsflow differences between twodeepwater risers. Ultimately inthis instance, one of the wellsfeeding Riser E was consideredto be an unstable producer andwas converted into a waterinjection well due to its impacton overall production.

ConclusionA TRACERCO Diagnostics™

Separator Study complementsother diagnostic tools and techniques available to produc-tion engineers. The technlogy isnon-intrusive with results gen-erated on-site. This allowsrapid understanding of fluidflow and mechanical integritywithin a hydrocarbon separa-

tion train by essentially makingthe process transparent. Thisapproach significantly elimi-nates guess work when tryingto resolve process issues andallows accurate process data tobe gathered providing informa-tion so that engineering deci-sions on process improvementor repair can be quickly madeand implemented. If deemednecessary, immediate changesto a system can be made withfurther measurements to assessif improvements have resulted.

If you wish to find out moreabout this technology, pleasecontact one of our technicaladvisors.


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Slugging Survey Riser E & FRiser ERiser F

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Density Measurement

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Figure 7 – Typical Slug Monitor Setup.

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Tracerco Insight V1 E2 4Qtr 08