SPE-169478-MSSuccessful Polymer Gels Application in a Highly Channeled Peripheral In-jection Well: Tello Field PilotG. Maya, R. Castro, J. Sandoval, Z. Pachon, R. Jimenez, K. Pinto, V. Diaz, J. Zapata, and L. Perdomo,[ECOPETROL S.A]; S. Muoz, [UIS]Copyright 2014, Society of Petroleum EngineersThis paper was prepared for presentation at the SPE Latin American and Caribbean Petroleum Engineering Conference held in Maracaibo, Venezuela, 2123 May2014.This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contentsof the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflectany position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the writtenconsent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations maynot be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.AbstractTelloFieldis operatedbyECOPETROLS.A. andlocatedinthe Upper Magdalena ValleyBasin,Colombia. It began production in 1972 and reached a maximum primary rate of 11, 200 BOPD in 1980.A peripheral water injection process started in 1997, reaching a maximum secondary production of 15,552 BOPD in 2000. From this date, water production has increased due to an unfavorable mobility ratio(M 3.5) and a high permeability contrast (Dykstra-Parson coefficient: 0.8 - 0.9). The current recoveryfactor is 22% and water cut is 92%.This paper summarizes from the laboratory to the field evaluation of a successful polymer gel projectforcontrollingwaterthiefzones, implementedasastrategytoreducethephenomenonofchannelingidentified between the injection well Te-49 and the producer well Te-46. The design includes laboratorytest (fluidfluid, fluidrockandcineticreaction)todeterminetheright polymerandthenecessarypolymer and crosslinker concentration to obtain consistency of the gel at the reservoir conditions.Polymer gel injection began in October 2009, reaching 43, 400 bbl of solution injected (13% of channelvolume) and being the largest Latinoamerican polymer gel treatment until now. Injection strategyconsidered a maximal polymer concentration of 7000 ppm and a fixed polymer/crosslinker ratio rangingfrom40:1tocontrol maximuminjectionpressure. Fieldresultsshowedanimportant increaseinoilrecoveries (oil production up to 300%) and a reduction in water cut (3%). Comparing these results to whatis normal obtained with this technology this is one of the most efficient process until now, this is morerelevant when taking into account the peripheral condition of the water injection.This work led to design and implement processes for water injection channeling control to improve theefficiency of water injection into other areas of the Tello field and other Colombian fields.IntroductionTellofieldwasdiscoveredin1972.ItislocatedintheUpperMagdalenaBasin(Figure1).Productioncomes mainly from the B1, B2, B3 and C units of the Monserrate formation, quartz arenites intercalatedswithlodolites.Thesedimentarydespostionalenvirometisdefinedastransitionalmarine.Theseflowunits are highly heterogeneous (Dykstra Parsons 0.8). The porosity range goes from 16 to 22%, andpermeability of the reservoir rocks goes from 80 to 360 mD.A peripheral water injection process began in 1997, increasing the field oil production; however, thewater cut increased rapidly to values of 92% due to the permeability contrast and unfavorable mobilityratios (M 3.5). The field oil recovery factor is estimated in 22% of the OOIP.Thewaterchannellingisoneofthefactorsthatmainlyaffectsthewaterinjectionofthefield, thischanellingispresentedthroughthesandswithbetterpetrophysical properties, specificallythosewithhigher permeabilities, making the secondary recovery process less efficient. Therefore, and as an optiontothefieldsituation,asearchforIORstrategiesthatwouldoptimizeoilrecoverywasperformed.Theselectedoptionistheimplementationofpolymergelstechnologyforreducingwaterchannelingintheinjecting areas.This work includes well to well production - injection history analysis, diagnostic charts analysis, fluidmotionstudyandgeological characterization, which, addedtotheevidenceof interferenceof wells,corroboratedtheexistenceofpreferentialflowchannelsanditsnegativeeffectsontheperformanceofwater injection.According to the analysis, it is evident the presence of thief zones causing severe water chanellingindifferentareasofthefield, duetopreferentialflowofinjectedwatertoareasofhighpermeability,whichadverselyaffectstheinjectionprofile; reasonwhypilot testsweredesignedtoreducetheflowcapacity of the thief zones to improve the efficiency of areal and vertical sweep.Once identified the channeled sands, experimental studies were conducted (fluid fluid, rock fluidand kinetics reaction) to determine the type of polymer to be used, and the polymer (partially hydrolyzedpolyacrylamide) crosslinker (Cr3) concentration ratio, to determine the characteristics of the gel thatbest meets reservoir conditions (temperature, salinity, and others).Finally, implementationof thefirst pilot wells for Ecopetrol S.A. was carriedout, includingtheperipheral injector Te-49, well QA/ QC(qualityanalysis/ qualitycontrol) analysiswasperformed.Figure 1Tello Field Location.2 SPE-169478-MSResultswereevaluatedbyestimatingtheincreaseinoil production, thereductioninwatercut andafinancial assessment involving surface facilities and necessary pumping equipment costs. Final result wasthat the technology generates feasible technical and economical results.Tello Field EvaluationTheselectionofthepilot areawasbasedonananalysisoffieldTello, developedtodemonstratethetechnical andeconomicfeasibilityofexecutingconformancetreatmentsusinggels. Thisanalysiswasdeveloped taking into account the current state of operation, including field visits to determine potentialbenefitsandlimitationstherein. ThemethodologyusedfortheevaluationofthefieldispresentedinFigure 2, which was adapted from literature.Figure 2Methodology for the control of water thief zones in injection WellsSPE-169478-MS 3Diagnostic and candidates selectionThis phase involveddifferent stages, withinwhichananalysis of influences betweeninjectors andproducers, identifyingdirectrelationshipsbetweenthem. PlateAofthefieldhastwoareas:northandsouth sector (Figure 3), a review of type maps was performed, which allowed to identify candidates forconformance treatments in the northern sector. Similarly, production curves were very useful forestablishing zones for possible conformance jobs. This zoning was necessary to connect producers withinjectors and verify the direct effect of every injector on the diferent influenced producers. The irregularityof the patterns is mainly because the water injection project in this field has been carried out peripherally(edge-water injection).Once selected Plate A of the Field, it was observed that in the northern sector there is strong evidenceof injected water channeling to the producers. As shown in production vs. Time (Figure 4) and WOR vs.Npcharts(Figure5), thereisastronglymarkedchangeintheslopesofthesecurvesapproximately7months after the start of water injection (December 1998) in the peripheral injector I-49 to the producerFigure 3Conformance pilot areaFigure 4Production rates vs. Time (Te-46)4 SPE-169478-MSI-46. This change is due to premature water breakthrough in the producing well, which, at the moment,was the only well draining the area.Injectionloggingtesrecords(ILT) of theI-49well, corroboratedtheresultsof theanalysiswithproductioncurves,indicatingthatmuchoftheinjectedwaterisbeingpreferentiallytakenbysandsB1(80%). This analysis (ILTs) combined with the distribution of open to injection and production intervals,contributed to the selection of the candidate well for the assessment of technology well conformance toimprove the profile injection.In general, the criteria for selection of wells candidates for application of conformance treatments aresummarized below:y Wells located in areas with high mobile oil remainingy Wells with clear evidence of injected water channelingy Wells with a history of poor vertical injection distributiony Low secondary recovery efficiency in the pattern (low recovery factor)y High flow rates with low pressure injectiony Injection pattern preferably confinedHavingintoaccount theaboveparameters, theI-49well was confirmedinorder toimprovethevolumetric sweep and evaluate the benefits to be obtained with the application of conformance treatment.However, it wasclearthat astheinjectionwell isperipheral therewasariskoflosingthechemicalmaterials into the aquifer.Polymer Gels TechnologyThe technology of polymer gels in hydrocarbon industry had its beginnings in the 60s. In 1968 DonaldC. Goetz, in the U.S. Patent 3, 383, 307, explained the formation of polymer gels and their use both, toreplace the water in a displacement process (polymer flood) and to blockage (chemical conformance). In1973, James W. Gall Patent wrote the U.S. Patent 3, 762, 476, concerning to groundwater permeabilitycorrection, by injecting polymer gels in the producing formations. The aforementioned first paper raisesthepossibilityofcorrectingthepermeabilityofaformationbyobtainingagelformedbybindingofapolymer with a metal ion, called crosslinker. The invention assigned to Gall detailing the need to injecta first volume of polymer - water solution at a specific concentration follow by the injection of a metalFigure 5WOR vs. Np (Te-46)SPE-169478-MS 5ion, hoping that both react in the formation to obtain the gel. The field applications of Galls invention,however, did not yield positive results for the reduction of water associated with oil production.In1987a newpatent was grantedinthe UnitedStates for the applicationof polymer gels inhydrocarbonreservoirstoR. SydanskandP. Argabright. Inthiscasethechemistryofpolymericgelsremains unchanged in its concepts, but this time the polymer and the crosslinker are mixed from surface,and are injected into the formation at the same time (water polymer crosslinker), then, a soak periodis given for the formation of the polymer gel.The technique developed by Sydansk & Argabright showed its efficiency when used in 29 treatmentsintheU.S. stateofWyoming. Thegreatestbenefitwasobtainedwhenthepolymergelswereusedininjection wells, so that the production of water associated with oil production influenced by the processconsiderablydecreased.Intotal,29treatmentsproduced3.7millionofadditionalbarrelsatanaveragecost of 0.34 USD per barrel.Because of the results described in the preceding paragraph, the technology of polymeric gels becamean important option for treating water injection process with characteristics of preferential flow. Numer-ous applications have been carried out since then, with positive average results.Thetechnologyof polymericgels (mixtureof ahighmolecular weight polymer polypartiallyhydrolyzed acrylamides - and a crosslinking agent - chromium triacetate - Figure 6) is a design to reducethe flow of water in high permeability formations. They have the ability to form in extreme conditionssuch as high concentrations of H2S, CO2, dissolved solids, and moderate temperatures ( 220 F). Oncethe gelation occurs at site, the water inflow into the well are usually reduced to less than 25% of the ratesof production pretreatment. This reduction in water permeability increases permeability to oil and allowsthe water injection process contact unswept areas.Polymer Gel Laboratory Evaluation for Tello FieldBeforethepolymer gel pilots, experimental procedures weredevelopedtooptimizethedesignandimplementation of the chemical injection process.Fluid fluid testsInitialsolutionswerepreparedwith12000ppmofpolymer(partiallyhydrolyzedpolyacrylamide)and5000ppmof crosslinkingagent intheinjectionwater. Fromthesesolutions four sets of gels wereprepared, for which the polymer concentrations ranged from2000 to 8000 ppm, with a polymer-crosslinker ratio 20:1, 40:1 and 80:1. Two sets of gels were stored at room temperature, while the othertwo were stored at reservoir temperature (160 C in this case).Figure 6Mechanism of gelation process for polymer gels6 SPE-169478-MSTothegelspreservedat reservoirtemperaturepotassiumthiocyanate(KSCN)wasaddedtoact asoxygen scavenger, in a polymer: KSCN relation of 10:1, in order to consume the dissolved oxygen presentand to minimize gel degradation. Additionally vacuum was generated to evacuate possible air (oxygen)present in each solution and sealing the tubes under partial atmosphere of nitrogen.Subsequently, the samples were kept under observation by the methodology of Sydansk at periods of4, 24 and 48 hours, 1 week, 2 weeks and 1 month as shown in Table 1 and in Figure 7.Through these analyzes and experimental evaluations, it was found that the polymer formed stable andstrong gels when interacting with the cross-linker in different waters and reservoir temperature, so it mightbe recommended for the treatment of the field, preferably at concentrations less than or equal to 7000 ppmof polymer and crosslinker relation 40:1.Fluid rock testThis stage consists of displacements in real formation plugs, previously characterized (basic and specialcoreanalysis)withapermeabilitycontraststhat allowrepresent different layerflowcapacities. Theseplugs are placed in parallel, as illustrated in Figure 8.Table 1Gel evaluation Tello Field.Figure 7Visual gel evaluation Tello Field.SPE-169478-MS 7Adisplacement test isruntolookfortheten-denciesthat governthephenomenainvolved. Thetest startswiththerestoredplugstoconditionsofirreduciblewatersaturation(Swir), andproceededtoperformacommonwaterinjectionforthethreecore holders until total water cut, adding all effluent,of98%,therebyobtainingabaselineandinjectionprofile. The system is brought back to Swir restart-ing the water injection process. When breakthroughof water in the first core holder is present proceedsto inject to the entire system the polymer gel in theselected test fluid - fluid, such as performed in fieldapplications, water injection resuming again until atotal water cut of 98%, resultingintheinjectionprofilemodifiedbythepolymergel. Resultsfromboth stages are compared to determine the benefit ofthe gel injection based on the total recovery system.A comparison of the results obtained clearly demonstrates the benefit of the polymeric gel injection.The plug that in the first stage did not allow water injection showed a recovery of 70% and; as expected,the other two plugs improved their sweep. The total recovery increased from about 40% to 78%. Figure9 presents a comparison of the injection profile before and after gel injection.Reaction KineticsThe velocity of a gel - formation reaction is studied in literature in terms of the storage modulus (G) forthe same. In this analysis the phase angle () between the storage modules and loss (G) is also important.Figure 10 shows the values of G and phase angle () in function of time. The behavior obtained identifiesthepolymerformingreactionasofpseudogelorder. Asthepolymericcomponentisinexcessinthesolution, stoichiometry is not considered. In the same figure, the behavior of the phase angle is important;going down and staying near zero values gel tendency to behave as a solid rather than a fluid. Reactionvelocity could be obtained from the natural logarithm of G, which presents different linear trends.Figure 9Injection profile comparison.Figure 8Parallel core holder equipment.8 SPE-169478-MSTreatment DesignAn estimation of the treatment volume to be injected was made. For this, the volume of the channel is themostimportantfactor, becausethegelvolumeinjectedisbasedprimarilyonapercentageofthetotalvolume of the thief zone or channel (5% to 30%). This volume was estimated from WOR vs Np chartsfor well channeled Te-46. It is assumed that the channel volume is the volume of oil displaced from thebeginning of the process of water injection and the abrupt change in the slope of the curve (see Figure 5).An increase in the slope of the curve WOR vs. Np means an increase in water production accompaniedby a decrease in oil (channeling effect).Accordingtoavailableliterature, thecritical parameter (apart fromeconomicconsiderations) thatdictates the amount of gel in most cases is the pressure response during gel injection. Typically, a rapidresponseandabrupt pressureriseindicatesthevolumeofthechannel isrelativelysmall, whileiftheinjection of the gel is not accompanied by a response of pressure, or slightly increased at the beginningof the injection, it is most likely to be an extended channel and hence higher volumes of gel are required.Therefore, it is of vital importance to determine the fracture pressure and the highest operating pressuretocompareeverymoment withtheinjectionpressurealongthetreatment, whichdictates necessaryvariations in terms of gel concentrations. Generally, wells with high delta pressure will be accompaniedby high concentrations of gel. This analysis is essential to check the possibility of application of any geltechnology.Pilot Implementation and MonitoringField application began in October 2010 in the peripheral injector Te- 49. For the implementation of thepilot, it was necessary to have the services of a specialized company in the application of technologiesdesigned to increase the recovery factor and improve the performance of water injection projects, whichinclude mobility process and polymer gel systems.During the treatment in Te-49 1000 Bbl / day of gel where injected at an initial concentration of 2000ppm that rose to 7000 ppm. For monitoring, physicochemical analyzes were performed by the QA / QC(quality analysis / quality control) team to the water injection equipment used to prepare the polymer andthe properties of the polymer and crosslinker solution (polymer concentration, density checked, viscosity,concentrationofcross-linker)wereverifiedallthetime.OperatingparameterswerecheckedtoensureFigure 10G y showing a seudo order relationship.SPE-169478-MS 9compliance in the times, amounts of materials and pumping volumes as scheduled to inject a volume of43, 400 barrels of polymer gels (Figure 11).Field operation is simple, surface equipment consists of a system for receiving and storing water (FracTank), an electric generator and an electronically controlled injection unit, which consists of a feed hopperpolymer, a crosslinker dosifier system, a mixing of the injected fluid (water, polymer and crosslinker) anda pumping unit triplex type.Polymer Gel Pilot Results and Project ExpansionThe evaluation of the conformance treatment in the I-49 well is conducted by comparing the productionof oil and water, before and after the process, besides the analysis of variables such as oil water ratios andwater cut. Evaluatinginformation, practically, it is thesameas discussedinthecandidateselectionprocess; however, it iscomplementedwitheconomicevaluationsandcomparisonwithother similarprojects.For evaluation, every well was reviewed individually; then, an overall assessment of the pattern wasdeveloped, including all the production wells associated with the injector. Subsequently, a collection ofevents from all wells involved in the pilot to abort the phenomena that may mask the response to treatment(extraction system changes, well repairs, etc.) was performed. Events in the wells were analyzed to reduceuncertainty about the increase or decrease in production fromclosures or openings of sands, re-perforating, isolations, packings, sand control, dropouts, etc., knowing in this way clearly when improve-ment is due to the direct effect of the gel injection.Themainobjectiveof theinfrastructureinstalledinsouthernColombiaistoincreaseby2%therecovery factor of the intervention area. According to the pilot phase results some wells have increasedproduction by 300% and decreased water cut by 3%. In Figure 12, the current production trend of oil rateand water cut from Te-46 well, well directly influenced by injection into the TE -49.To date there have been produced 173,000 bbl of incremental oil in the Te- 46 well of 340,000 fromallwellsinfluencedbythepilot,andatotalof450,000BblexpectedtoDecember2014(10timesthevolume of injected polymer gel, surpassing results reported in literature for this type of projects, wherebetween 2 and 3 incremental oil barrels per barrel of injected gel are expected). Table 2 presents treatmentFigure 11Pumping conditions T-49.10 SPE-169478-MSconditions of polymer gels injected around the world, including the case study of this paper. From thesedata it can be analized the relationship between some design variables, such as channel volume and thepercentageofinjectedtreatment gel, anditsinfluenceontheincremental oil that canbeobtained. Acomparisonbetweenthetreatment performedonAgFarms, whichhasarecoveryfactorclosetotheTellos pilot, and a small percentage of gel used, the results of incremental oil for Te- 49 are much better.Havingintoaccount datapresentedinthetableaboveandestablishingarelationshipbetweentheamount of injected gel and the recovered oil, there can be obtained a graph as shown in Figure 13 wherethetrendlineshowsthatforsmallpercentagesofthevolumeofthechannelinjectedasgeltreatment,small values of incremental oil are obtained; while if the percentage of the injected gel is above 30 % thevalues of incremental oil obtained are much larger, making the cost per incremental barrel recovered muchlower. The chart also shows that a pair of points are above the trend, in the case of Minnelusa # 1 and Te-49 where greater oil recovery in relation to the volume of gel used is shown, these results are attributedFigure 12Production trend in proucer T-46.Table 2Bulk gel treatments in matrix rock with crossflow.FieldChannelMPV, BblsGel Volume% MPV*Inc. Oil% Gel VolCost$/IBO**Recovery% OOIPOther PolymerProcess?Time to GelResponseResponseDurationAg Farms 271000 6.7 219 1.46 24.9 Yes 6 Months 4YearsAsh 30000 35.4 424 0.85 21.2 Yes 18 Months 2.5 YearsIndian Tree 70000 41.9 499 0.37 17.8 No 1 Month 2 YearsN. Rainbow 584000 10.0 308 0.71 41.1 Yes 1 Month 3 YearsRaven Creek 1036000 4.5 108 3.32 53.0 No 6 Months 3YearsMinnelusa #1 325000 9.0 443 0.62 30.4 Yes 3 Months 2.5 YearsWD 10000 69.0 - - 31.3 No 1 Month 2.5 YearsBreed Creek 60000 29.8 447 1 24.5 No 6 Months 2YearsHawk Point 5000 50.0 - - 43.3 No9 Months -Te-49 323000 13.4 1000 2.58 22 No 2 Months 4Years*MPV- Moveable Pore Volume in Channel**Gel treatment cost per incremental BBL of oil recovered as a result of the treatmentSPE-169478-MS 11to the gel volume applied, although Minnelusa #1 differs from Te- 49 because it had already previouslyhad other polymer treatment.Due to good results, expansion of the process was designed for the Te-4, I-7, I-61, I-23, I-37 and I-38wells of the field and for other Ecopetrol S.A. fields, MG-54, MG-1, SF-179, SF-104, SF-13; in which,in general terms very good technical and economic results have been obtained.In terms of net present value results are 9.1 MUSD with an investment efficiency of 7.94 (2.58 USDper incremental oil barrel).ConclusionsThe technology of polymer gels for thief zones control is an option that can be used as a complement tooptimize water injection processes, also applies to peripheral injection processes in highly heterogeneousreservoirs.Thedesignedmethodologyreducestheinherentriskofapplyingchemicalconformancetreatments.The steps described in this work increase the chances of achieving positive results in optimization of waterinjection.The study developed not only allowed to implement the first pilot of the technology in Ecopetrol S.A.,also allowed the incorporation of laboratory protocols and engineering analyzes required to return feasiblethe technology and make it an option for optimizing reservoir.AcknowledgementsThe authors express their gratitude to Ecopetrol S.A. for allowing the publication of these results and fortheir generous support throughout the project. Particularly to the Reservoir Management (GDY), Huila -TolimaSuperintendence(SOH)andtheColombianPetroleumInstitute(ICP). AlsototheproductionchemistrylaboratoryoftheICPandtheCompanyTIORCOforitsaccompanimentandsupportinthedesign and execution of the field work.References1C. Norman et al. A Review Of Over 100 Polymer Gel Injection Well Conformance TreatmentsIn Argentina And Venezuela: Design, Field Implementation And Evaluation SPE 101781. 2006Figure 13Relationship between gel volumen injected and incremental oil recovery.12 SPE-169478-MS2G. Maya, et al., Polymer gels for Controlling Water Thief Zones in Injection Wells., JournalCIENCIA, TECNOLOGA y FUTURO CT&F, Volumen 4 nmero 5 Pg 3744, 2012.3Smith, J., and Larsen, D., Bulk Gel Treatments for Reducing Water Injection in High Perme-ability or Fractured Thief Zones and Water Shut-Off in High Water-Cut Producers, Presentedatthe2ndAnnualInternationalConferenceonConformanceProfileControl,Crouse&Asso-ciates, August, 1996.4Smith, J.E. Practical Issues with field injection well gel Treatment, SPE 55631, presented at the1999 Rocky Mountain Regional Meeting, Gillette, Wyoming, USA.5Sydansk, R.D A strategy for attacking excess water production SPEPF (August 2003)6Sydansk, R.D., ANewConformance-Improvement-TreatmentChromium(III)GelTechnol-ogy, SPE/DOE 17329, Presented at the SPE/DOE Enhanced Oil Recovery Symposium, Tulsa,OK, April 17-20, 1988.7Sydansk, Robert D., and Moore, Phillip E., Gel Conformance Treatments Increase Oil Produc-tion in Wyoming, Oil & Gas Journal, January 20, 1992.8UNITED STATES PATENT OFFICE. Conformance Improvement in a Subterranean Hydrocar-bon-Bearing Formation Using Polymer Gel. Inventor: R. SYDANSK and P. ARGABRIGHT. Int.CL.:E21b33/138. Fechadesolicitud:27, enero, 1986. USPATENT4, 683, 949. 4, agosto,1987.9UNITEDSTATESPATENTOFFICE. GelingAgents, GelsandMethodsfor FormingGels.Inventor: D. GOETZ. CL.: 252316. Fecha de solicitud: 30, julio, 1964. US PATENT 3, 383,307. 14, mayo, 1968.10UNITED STATES PATENT OFFICE. Subterranean Formation Permeability Correction. Inven-tor: J. GALL. Int. CL.: E21b33/138, E21b43/22. Fechadesolicitud: 3, enero, 1972. USPATENT 3, 762, 476. 2, octubre, 1973.11Wouterlood, C.J. et al. Aspectos del desarrollo de un reservorio heterogneo bajo recuperacinsecundaria. Presentedat the tercer seminarioInternacional ExploracinyExplotacindelPetrleo y Gas. INGEPET 1999. Lima, Per.12Wouterlood, C.J. etal. ConformanceImprovementwithlowconcentrationpolymergelsinaheterogeneous, Multi-layer Reservoir SPE 75161. 2002SPE-169478-MS 13