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
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