retrograde condensate dropout phenomena

8/12/2019 Retrograde Condensate Dropout Phenomena

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D.B.BENNION, F.B. THOMAS, B. SCHULMEISTERHycalEnergy Research Laboratories Ltd.

AbstractCja i conllcn i:IIC rcscrvllirJI cxhihiling cla i iic ..c.lcw p)in\ llr

rclrllgr-oidc cllnc.lcn i:1\C drop I'" heh.lvilltlr cxi il in nulny arc.l~ inI~ world. Tht.-sc ~n'llirJI :trc unilluc in that. :t i lhe ~n'llir(M\.~ iUre i i I.k.",-"n ~. :t ccnOlin voluntl: of the l1.::tvy ~oo froclilm11I'lhe ga.. i.'i pn.",-"ipil:tI\.'tI in liquid rum1 fmm ~llulil1n in 111.: a i.n1i i cllnd~n iOlle liquid may b~ Icmpl)rolrily I)r pc:rn1ancnlly1r-"p )I..'tI n Ihl: re.'il:rvrnr. c:l'I iin~ .'iI:Vl:rc n.'tIuctitln i in ~0I i prll-dOClilll1 rol,-~ aoo the pc:nn.lncnl 10 i...ur :I l..rgc Ixlnit)n uf Ihc\'uIOllik: ;tOO v:lluablc: \...mc. cn.'iale iquitb Iduc: 10 cOlpill;ary pre i-"lIre-iIWlM:\.'tI 1r;lpping .:rrt.",-"ls n the plnlU.'i tnc:tlial.

Thi i p.lp.:r rl:vic:\v~ Ih.: h:l~ic Ih':l'ry l)r g.l i cund.:n iollcJrI)pllllI alw c.Ic~bc i. in l.k.'1O1il. .lm:lgc pnml':l11 i Ih:ll nUlY 11.:;1 i~M:i:tIt.'tI with pnxlOClil1l1 of rc.'il:rvl)jrJI I" Ihi i Iyp.:. Tc:chniquc ifllr Inilig:tling coOOc:n i:l\c droptlul prubl.:m i I)n :I pnxlUClil)nhol ii i. a.. \vcll a~ ililnulalilln 1t.",-"hni'IU\.~..uch a.. rcpre i...uriwlilln.I.:an alw rich gol i inj,:clil)n. iurr:lctanl and ~)I\'.:nl inj.:ction. iniilU l:'tlnhU ilil)n :tnd w:tlcr/ga.. injt.",-"lilln. .Ire re\"ic\vt.'tI. :too 11)t::KI\"anI3g': i 31xJ di ll.lv3nl:t~'C i l" 111.: t.'ChniqlJl: i di~'t i."'-'tI.

Formation Damage Issues in GasCondensate ReservoirsThe literature s repletewith detaileddiscussions n fonnationdamage


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ing situations, as many gas condensate eservoirs at discoveryconditions are at or very near the dewpoint pressureof the gas.Even modest drawdowns applied n order to achieveeconomicproduction rates result in sub dewpoint pressure productionaround he producingweDs.Drawdown can be reduced n many casesby increasingeffec-tive bottomhole low area hrough he use of high density perfo-rating, open hole completions, horizontal wells and, in somecases,even by small fracture treatments if fracturing wiD notresult in water/oil production) in order to increasebottomholeflow areawhich can educedrawdownanddamage ffects.lion process s extremelymass ransfer imited (diffusion motivat-ed) andhencevery slow. Also, since sucha limited volume of gasis in contactwith a given volume of condensaten d)e pore space(the condensate hich s ttappedhaving beenprecipitatedout of ahuge volume of gas w~h has flowed through d)e pore space ncomparison o the relatively small volume present n contactwithit under static exposure), this once again severely limits theamountof revapourizationhat can occur.In a similar fashion,static mbibition (capillary pessure effects"wicking" the ttappedcondensate way from d)e wellbore deeperinto the formation) are only effective if the reservoir exhibitsstrongly oil wet naturalwetting tendencies.f d)e reservoir s neu-tral or water wet, therewill be no spontaneousmbibition affinitypresent o move the trappedsaturationaway from the near well-bore region. Since many gas reservoirs do not contain a liquidhydrocarbonsaturation nitially, by default, in many cases,d)eyare water-wet in nature, and hence his negates mbibition as ameansof drawing retrograded ondensateiquids away from thewellbore.Examinationof Figure I also ndicates or some eservoirsitua-tions that if the pressure s dropped low enough, condensatebegins o revapourize nceagain. n some nstances,t is possible.at very low pressures nd high temperatures,o pass completelyout of d)e two-phase egion (through d)e "bottom" dew point lineas llustrated n Figure I). Practically, once again, his med1odslimited in application. n most cases, he pressureat which sub-stantive revapourizationbegins to occur is well below the ec0-nomic abandonment ressure f the reservoir. Even if this is notd)e case, he re-vapourization rocess ends o be extremely slowand mass ransfer-dominated hen occurring n a static situationin porous media (in comparison o an agitatedvisual cell systemin which the PVT measurementsre normally conducted).

Mitigation TechniquesIn most situations, a certain amount of damage due to conden-

sate trapping is unavoidable. This is even the case in a gas cyclingoperation as, in general, although the bulk of the reservoir ismaintained at some pressure above the dew point value, the areaimmediately adjacent to the wellbore is often subjected to highdrawdowns which still result in localized condensate dropout Ingood quality reservoirs where the value of the critical mobile sabl-ration is low, this dropout may not appreciably affect flow rates(at least while reservoir pressure is high), and conventiODal prima-ry production may be the economic and technical option ofchoice. In many cases though, periodic treatments to attempt to"remove" a portion of the trapped condensate liquids from aroundthe wellbore are often used to try to increase production rates.

There are a number of potential techniques that have been sug-gested or used recently for this purpose with varying degrees ofsuccess. They include:

1. Static repressurization and imbibition2. Lean gas injection3. Rich gas injection4. Solvent injection5. Mutual solvent injection6. In situ combustion7. W ater injection/displ~t

Lean Gas InjectionThis technique enjoys more success, but generally requires rel-

atively high bottomhole pressure in order to be successful. Leangas injection is generally conducted using either dry methane ornitrogen gas and uses high pressure vapourizing miscibility toextract the trapped condensate from the injection region ~-ing the wellbore. In this case, because the injection gas is lean innatum and contains 00 heavy end fraction, it has the capability ofextracting a considerable amount of heavy ends from the system.

Static Repressurization and ImbibitionThe enant of Ibis technique is based on the assumption of her-

modynamic reversibility. Examination of Figure 1 indicates that,theoretically, if production from the well is baIted (shut in) and ifthe bulk reservoir pressure is still high enough that over time thepressure in the depleted region around the weUbore is increased toabove the original dew point pressure, the condensate liquidswhich are trapped in the pore system should be "re-vapourized"into the gas phase.

Unfortunately, this technique enjoys limited actual success inporous media due to the limited interfacial area, the revapouriza-6 Journalof CanadianPetroleum ~-:.ok)gy


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lutes one misciblehydrocarbon hase or another. n many cases,the IFf between he reservoirgas and an organic solvent, such axylene. is actually higher than that between he trappedconden-sateand he reservoirgas,which may actually result n an ncreasein trappedhydrocarbon hase aturation.Mutual Solvent/Surfactant Injection

This includes he injection of high molecular weight alcohols(i.e., butanol), ochermutual solvents and surfactants.The objec-tive is to reduce he gas-condensateFf which makes t easier orecover he ttappedcondensatee.g., owers the value of the criti-cal condensate aturation).Many alcoholshave sludgeand emul-sion problemswith condensates nd careful compatibility testingshould be conducted.Often with many agentsof this type, theactual reduction n gas-oil IFf is relatively slight and the overallstimulationeffect may be marginal.Careful 1FT and ab screeningshould be conducted rior to execution o determine he effective-nessof any agentof this type or condensateemoval.In Situ Combustion

This is a fairly novel technique which attempts o useair injec-tion to ignite and "bum" the trappedcondensate ablrationout ofthe region n the nearwellbore &rea.Most condensates re volatilein nature and will spontaneouslygnite at reservoir emperaturesover about 120' C.Concernswith this method nclude high bouomhole empera-tures aDdcementdegradation, ffective propagationof the flood,ccxrosionCUICemSnd well flashback.explosion) coocems f allof the injected oxygen is not consumed by combustion andLTO/HTO oxidation eactionswith the n situ crude oil.Considerable esean:hwort is cunently underway evaluatingthe use of this method.Accelerated ate calorimetric studies


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sate s removed rom dte nearwellbore&rea, ontinuedproductionbelow the dewpoint pressure esults n the recurrence f accumu-lation problems. The economics of the treatment will thus behighly dependent n the magnitudeand ength of the "flush" pr0-duction period that is created after the stimulation treatment scompleted.

Provenance-Original Petroleum Society manuscript,Retrograde Condensate Dropout Phenomena in Rich GasReservoi~Impact on Recoverable Reserves,Permeability,Diagnosis, and Stimulation Techniques (TN2001-078), firstpresentedat the Canadian nternational Petroleum ConferenceJune 12-14, 2001, in Calgary, Alberta. Abstract submitted forreview December 12, 2000; editorial comments sent to theauthor(s) August 20, 2001; revised manuscript receivedSeptember19,2001; paper approved or pre-pressOctober II,2001, inal approvalDecember , 2001.&ConclusionsThe mechanism of condensate dropout from rich gases hasbeen discussed as one of the potential mechanisms reducing theproduction rate aJKI~verable reserves of condensate liquids. Ingeneral, the value of the critical condensate saturation in porousmedia varies from I - 40% and is affected by IX>legeometry, wet-tability, interfacial tension and capillary pressure and drawdowneffects. In most situations, porous media with in situ peImeabili-ties greater than 1,000 mD exhibit low (less than S%) critical con-densate saturation values. Fonnaboo damage aJKI rapping issuesare generally more severe in lower quality (sub-lOO mD) forma-tions which exhibit more adverse capillary pressUIe characteris-tics. Means of reducing dropout problems, as well as remediationtechniques such as represurization, lean and rich gas injection,solvent injection and in situ combustion have been presented andthe specific advantages and disadvantages of each methodreviewed.

Authors BiographiesBrant Bennion is Hycal's presidentand sI a project engineer with over 20 years ofdomesticand ntematiOllaJechnicalexper-tise in the area of formation damageandfluid flow in porous media. Brant hasI authoredor co-autbored ver 170 technicalpaperson a variety of subjecu, includingmulti-phase low in porous media, forma-tion damage,underbalanced rilling, fluidphase ehaviourand enhanced il recovery.Brant received his B.Sc. in chemica] andpetroleumengineering rom the University of Calgary with dis-tinction in 1984.BraDt eceivedBest TechnicalPaperof the Yearawards rom the PetroleumSociety n 1993 and 1995.Brant is adirector of the PetroleumSocietyand s also a ~ber of APEG-GA and SPE (registeredP Eng). Brant wu also chosen o be a"DistinguishedLecturer" or the SPE or 2001.

Brent Thomas is Hycal's senior vice-presidentand s a project engineerworkingin the areaof numericalsimulation and gasI injection. He received his Ph.D. fromWashington University in chemical engi-neering.Brent hasover 20 yearsof domes-tic and internationalexperience n die areaI of numerical simulation, gas injection,phase behaviour, solids precipitation, and- - chemical and thermal application. He has...uthoredor co-authoredover 130 technical papersand receivedthe 1992 Best Technical Paper of the Year award from thePetroleum Society (Experimental and Theoretical Studies ofSolids Precipitation rom ReservoirFluids). He was selectedasa"DistinguishedAuthor" for die PetroleumSociety n 1995.

Bernie Schulmelster is the engineeringmanagerat Hycal. He brings with him 20years of industry experience, S of whichare directly focusedon laboratory researchand services.He maintainsa strong echni-cal background n the areasof petrophysicsand onnation damage ssessmentnd con-trol. Experiencedn managingandconduct-ing applied studies n all ~ of advanced-- - core analysis. Currently responsible foroverseeing he engineering unction of our integrated projectswhich includesspecialcore analysisand phasebehaviour.Bernieis a graduate f the SouthernAlberta Institute of Technologywitha diploma n petroleumengineering echnology.

AcknowledgementsThe authors expressappreciation o Hycal Energy ResearchLaboratories or permission o present his materialand to VivianWhiting for her assistancen the ~on of the manuscript.REFERENCES

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8. YEAGER, V.J., Use of Downhole Diagnostics EnhancesDetermination f DamageMechanisms; r,s,nt,d at th, SPE1ntmlatiOftal SJIIIposium 011FomlOtion Damag' COIIIrol. 1A/aY'II"U, SPE 39466, F.bruary 18 -19, 1998-9. BENNION, D.B., PomI8tiUI Damaae During UncJerl)a1aIICed ndOverbalanced Drillinl Operations; Ph.D. Th~sis, Univ~rsity 0/Calgary,200J.10. Y ANNlMARA, D. V. and -nPPIN, D.L, ScreeIIing of Oil fw In SituCombustion at Reservoir Conditions Using Accelerating RateCalorimetry; ~r SPE 27791, pru./lt.d and tM 98' SPE EaRSymposium.ul.ta.OX,April 17-20,1994.

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retrograde condensate dropout phenomena

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