SPE-24630 Evaluation of Horizontal

7/25/2019 SPE-24630 Evaluation of Horizontal

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SPE 24630

Evaluation of

Sorktyof PatrobwnEnglneer8 1Horizontal, Radial, and Vertical Injection Wells

in a Pilot SteamfloodS-M. Bulier, Unocai Corp.SPE Member

Copyrigh t 1992 , Society o f Pet ro leum Engineer s Inc.

Th ta paper was prepared for p reaan tat lon at the 67 th Annual Taohnlcal ConIafenoa and Exhibi tion of the Society of Pet ro leum Engineer s held In Wash ington , 00, Or20bar 4-7, 1S62,

Th is papar was W1OCM for presen tat ion by an SPE Program Commit tee fol lowing rev iew of lnfor rnat lon confained in an abat raa f aubmlt fed by the author( s) . Conten ls o f the prqwr,aa preaenled , hava not been rev iewed by the Soolety of Pe troleum Engineer s and are sub ject to cor rao tlon by the au thor (s ). The mater ia l, aa p reaantad , doaa not naceaaar lly ref laotB ITY W@t kr n o f t h e S@@ OfPetrolaumEn91neare, It Offlcere,w M@WS. PawfaPfaaantadatSpE meet ings are aub lao t to pub li cat ion rev iew by Editor ial Commit tees o f the SOC etyof PeWAaum En@nears, Parrnia ion to copy lareatr icfad to an abafraot of not more than S09 wc+ds. Matrat lonfr may not be cop ed. The abatraat shoufdcontain oonapkwua aoknowtadgmanto where and by whom tha papar i s p resen ted . Wr it e L lb rarkm, SPE, P.O. Sox 833636, Richardson , TX 76023-SS36 U.S.A. Telex , 724920 SPEDAL,

ABSTRACT

A uniquepilot steamfio~dIncorporatesone horizontal,one radiai, and three vert cai steam injection weils,The horizontal and radiai weiis were designed to

aiievlatesteamoverrideand improvesweepefficiency.The horizontal injector is a medium radiusweii with400 of completion Inthe horizontalsection. The radiaiweii has four compieted, near-horizontal, uitra-silortradius Iateraisdriiled within a short verticai section.The verticai injectors are conventional completions,with perforationsin one or two sandiobes. Productiondata from offset producers, injection profiie data,produced fluid and downhoie temperaturedata, and acomprehensive iog suite conducted on three

temperature observationweiis.were used to comparethe three injection strategies. Whiie a significantincrease in oii production has not yet been seen,changes in water production, cut and flowiinetemperatureprovideciear indicationsthat manyof theoffsets are being affected by steam injection,

Tt e piiot steamfloodis located in a 5 acre area in the

ioca lzed,previouslyunswept,portion of the thick, sub-homogeneousreservoirbeing steamflooded, To date,the radiaiweii hasbeen Usedas a huff-n-puffproducer.Despite the short steam injection periods, producerssurrounding the weii have responded dramatlcaiiy.

Observationweiidata, ratesfrom offsetproducers,andtemperaturesin the offset producers confirm that theverticai injectorsare distributing heat and affecting oiiproduction iess effectively than the horizontal andradia methods.

lNTROLXJCTiON

UnocalsBremerFeeis iocated in the northern portionof the Midway Sunset Fieid, approximately 35 miies

westof Bakersfield,California(Figtire1). The propertyconsists of 360 acres entireiywithin Section 16,T31S,R22E, MDB&M, Approximately 180 acres areproductive, Current production averages5,000BOPf3from 247 producing weiis, Aithough the fvlafvic,DnChannei and Speilacy horizons have been producedsporadically,aii production from the iease is currentiyfrom the Potterformation


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-, *.,

EVALUATIONOF HORIZONTAL,RADIALAND VERTICALINJECTION WELLS2 IN A PILOT STEAMFLOOD SPE24630

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provldlngfurtherevidencethat injectingthe steamintounsweptzones could provide Incrementalreserves.

The pilot steamfloodconsists of six invertedfive-spotpatternsonapproximately5/8-acre spacing(Figure2).Two of the patternsare affected by horizontal injector1-49. Three vertical Injectors ( -50, I-51, and 1-52)impact three connecting patterns. Radial well RI-53affects four producers separated from the otherpatternsby one well spacing,

RESERVOIR, CHARACTERISTICS

Q@Q9Y

The Mio-Plioceneage Potter formation Is a massivesand sequence deposited in a shallow waterenvironmentas grain and debris flow turbiciites. ThePotterunconformablyoverliestheAntelopeShale. TheTulare formation truncates the top of the Potter,causing the Potter to pinch out in a northeast-

southwest direction approximately 800 north of thepilot area. A typical induction/GR log is shown inFigure3.

Structure on the property is a southeast trendinghomocline with a dip of 10 increasingto 30at thebase of the productive interval. There are norecognized faults, Top Potter in the pilot area is atapproximately +1,500 s,s., 250TYD.

The Potteraverages650 in thicknessin the pilot area,of which approximately 400 are currently productive,TheremainingPottersand is steam/air saturated, ThePotteris separatedbydiatomaceous claysor siltstonesinto the B and Czones. The existenceof separatesteamchestsbelow hese Individualsilts suggeststhatthese zones serve.aspermeabilitybarriers.

.,

temperaturerangeof 150F to 250F, viscosityvariesfrom 520 cp to 25 cp. Current reservoirpressureinthe southwestarea of the ieaserangesfrom 50 to 150 .PSI.Table1 providesa summaryof pertinent reservoirdata.

PILC)TDESCRIPTION

The location of the pilot was chosen to (1) providesimilarstructuralpositionamong the injectors,therebyfacilitating comparisons between injection methods,

and (2) maximizefuture development potential. Fournew injectors, one radial cycilc producer, and threeobsetvatlon wells were drilled in May and June 1990.Detailedinformation on the drilling of these wells canbe found in Reference1.,The seventeendirect offsets(producers)weredrilled between1977and 1984;eightwere dd led in 1984.

Well I-49, is ~ medium radius horizontal well. Tots .measureddepth is 1,480at a vertical depth of 937.The well is completed in the Potter C zone with 400of slotted iiner in the horizontal section (Figure 5),Although it was drilled as a continuous injector, an ,~fiernpt Wasmade to produce the well. After severalpwnp changes required due to sand production, s5,000 MMBTU steam aycle and a foam cfeanout, econom c rates were not achieved. The well wasplaced on continuous injection In Ju y 1990 at ratesconsistent with the other new injectors but at a lowertubhg pressure,

W,?ll Ri.53 was dri[l~ as a joint lfnocai/Petrolphyslcs/DOEproject.2aEight ultra-shortradiusradialswere drilled in the verticalsectioribetween881and 885 MD (Figure6). The radiais ranged in lengthfrom 14to 103. Four of the radialswere completed,one withaflexiblesand barrier (FSB)4,two with gravel


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S. M. BULLERPE 24 30

PILOT EVALUATION

Producers

Production response was evaluated using dataacquired on a daily basis (measuredtotai fluid rate,oakulated oii rate, measured cut and measuredflowlinetemperature),calculatedmonthlyaveragedata(gross,net and cut), and annulartemperaturesurveys.Pilot production is also comparedto production fromthe existingsteamflood,

.. i)ailv Production DataBased on daily production data, sevetd welis haveexhibited an obvious responseto continuous steaminjection in i-49. For instance,Bremer183sgross ratehas remained steady since horizontal well 1-49 wasplaced on injeotion (Figure8). Oii production is on anincline. Flowfine temperature is 50F higher thanbeforeinjection began in 1-49,and hasremainedhigh.Cloudingthe anaiysis,however,isthe fact that the wellwas cyofed two months after i-49 went on iine.

Despite that fact, it is obvious that the well is notshowing the response typical of cyclic steam; it isthereforeassumedthat the responseis dueto injectionin i-49.

Analysis of other wells is not as ciear cut, Forinstance, Brerner 103 (Figure 9) appeared to beresponding to injection in i-49 just prior to beingsteamed In January ~991. Gross prwiuction thendropped in a typicai cyclic fashion. The well wassteamedagain in January 1992and [sshowinga goodinitial response.

Twowellsin RI-53spattern respondeddramaticallytothe radial wells second steam cycle. Whether thisresponsewasnot seenuntil the second cycle is due toIhe unusually large volume of heat injected (10,000MMBTU d i } i i l f

patterns seem to have responded to continuousinjection. For instance,Bremer102(Figure12) showsa fahly constant net rate since 1-50and I-51went oniine. The well has not been cycied for almost threeyearsand stillexhibitsa flowlinetemperatureof 17SF.However,just downdip from 102, Bremer189 (Figure13) has shown a negative responsq water cuts areapproaching 100%,unaccompaniedby an Increaseingross production. This type of responseis a classicindicaticm of steam channeling and prematurebreakthrough at the producer. Since this wet isdowndip from the injectors, a Iocaiized steamchest

might have been present in the area around the well,enabiing the steamto travel against the natural updippreference.

Thistype of analysisis admittedly vei-~subjebtfve,andis aiways clouded by interferencefrom steam cycles,mechanical problems, inaccurate well tests, etc. ~ ,Keepingthis subjectivityin mind, an attemptwas madeto graphicallysummarizethe effectsof steaminjectionon each producer (Figure 14). Changes In oil

production, oii ratedecline, flowtinetemperature,andcut are depicted in four quadrants of a circlesurrounding the wail. A plus sign (+) indioates apositive response, e.g. oil production higher thanbefore steam injection started,deciine rate shaflower,flowfine temperature up, cut down. in sores cases,decline rate is lower ~+ for decline), but oifproduction is not actuaffy higher than beforecontinuous injection started (production quadrant leftblank). A minus sign (-) indicates a negativeresponse,e.g. cut higher. A zero (O)indicates nodiscernibleimpact, whiie a question mark (?)is usedwhen the effects of steam injection are masked byinterference from a steam cycle or mechanicalproblems.

Patternaverageflowline temperaturesare also showni Fi 14 Th h h i l il


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EVALUATIONOF HORIZONTAL,RADIALAND VERTICAL INJECTION WELLS4 IN A PILOTSTEAMFLOOD SPE 24830

havenot. Ingeneral, updipproducers arerespondlngno better or worse than downdip producers.

Monthlv Production DataMonthlyproduction datawas analyzedinthreegroups:1) the horizontal Injector with its SIX surroundingproducers,2) thethreeverticalInjectionwellswith theireight immediate offsets,and 3) the radialwell with itsfour surrounding producers, Figures 15 through 17Include production rates, steam injection rates,instantaneoussteamoil ratio (SOR)and water cutsforeach group. $lnce the radial well has to date beenused only as a cyclic producer, that groupsproduction is not Indicativeof responseto continuousInjectlort. The three vertical well patterns weregrouped together to facilitate comparisons betweeninjection strategies. Attemptsto quantify the responseof individualvertical well patterns are not inc uded inthis report.

The monthly data suggeststhat none of the groupshave shbwna sustained Increasein oil production asa result of continuous steam injection, ~ Waterproduction on the other hand,hasincreasedmarkedlyin both the horizontalgroup and the vertical group. Itis significant to note that while both of these groupshaveseen a similar increaseIn gross production @OOBPD),,he instantaneousSORfor the horizontalgroupis muchlower (3to 4) than the vetiical group (4to 8).This would Indicatethat the same response in gross

production is beingeffectedin the horizont~lgroup bya smaller amount of steam. If Increased waterproduction is a precursor to increased oil production(as it was in the northeast portion of the lease), thelower 30R in the horizontal pattern could signify thatthe goal of a more efficient,verticallyfocused drive is

being accomplished.

The spike is almost non-existent in the well furthestsouth in the pattern (Bremer 151), and peak

temperature in that wel Is 13F lower. This trendIndicatesthat heatinjectionIsdecreasingwith distancealong the horizontal completion. To confirm theseresults, a direct measurement of the steam injectionprofilethrough coiledtubing production logging will beattempted in the near future.

A similarcrosssectionIncorporatingthe downd pwellsand the out-of-pattern producer,(Bremer261) revealsa much less pronounced heatedzonein the horizontalpatterns (Figure 19). Peak temperatures are 25to30F lessthan in the updip wells,

Temperaturedata for the wells in the vertical patternsis sparse (two wells could not be suweyed) anddifficuit to interpret, On the updlp side (Figure 18),Bremer 150A shows a temperature rise in the samestratlgraphic Intervalthat is 10OFcolder in well O-3,just 150 to the north. On the downdip side (Figure19), Bremer 189 shows an anomalous temperatureincreaseat the botlom of the weli, peaking at 260*F,the highest recordedtemperature of any of the wells.Just one location south, however, 13remer193showsno evidenceof continuous injection. Bremer64, the ,next well to the south, shows some evidence ofInjection in 1-52.

The shapeof the temperatureprofiles Inwells 187and261, the out-of-pattern producer, are similar. It is

significantto note, however,that the peak temperaturein the affected intewal is 25F lower in the out-ohpattern producer.

Com~arlsonWith Existina SteamfloodThe production responseseento date in the pilot areais very consiste~t with steamflood response In thenortheast portion of the lease Figure 20 shows


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SPE 24630 S. M. BllLLER 5

to steamflood pattern area, pay and injection rate tothe time required for response in the existingsteamflood suggests that oil production in the piiotverticai patterns shouid begin to increase sometimearoundJune 1992,two yearsafterthe start of injection.Afthoughthe actuai mechanics of steam zone growthare obviously more complicated than simpie ratioswouid suggest, in this case they provide a roughestimateof when to expect response.

Observation Welis

Temperatureand Duai S~acedNeutron LOCISFigures 21 through 23 show the foilowing data: 1)resistivitylogs for both the observation weii and thenearestinjector, 2) the temperatureprofiiesthat havebeen obtained, and 3) an overlay of the far sensorreading of a duai spaced neutron iog. The overlay ofthe current (4/92) vs. the initial neutron data providesa qualitative evacuationof current gas saturation vs.initialgas saturation, Aii observationweiis are iocatedupstructurefromthe correspondinginjector,or injectorweii path in the case of the horizontal weil, Theobservationweii for the horizontalinjector is downdipof the vertical (iogged) portion of the horizontal weli(asdepicted in the N-Scrosssectionin Figure21), butupdip of the horizcmtaiweii path, Distancesfrom theinjectors range from 55 to 100.

Figure 22 shows that up until a short time ago,injectionin o weii i-51 had not significantlyaffectedO-3. In starkcontrast is the majortemperatureelevation

which occurrsd very rapidly in O-2, the observationwell opposite the horizontal injector (Figure 21). Thetemperature in the sand iobe where the horizontalinjector is completed has risen 160F, and thetemperature rise has been fairly confined verticaiiy,The far data overlayaiso showsa significant increasein gas saturation in the samearea, These resultsaresignificantfor two reasons: 1) the observationweli is

steam cycie dissipates over time, the temperaturedifferentiationis iost and the heat distributionappearshomogeneous, Hereagain, the impact is ciear: wheninjecting steam,the radiaiweil is focusing the heat intwo very distinct verticai intefvais.

GSTand C/O Leas ,A Gamma Spectroscopy Tool (GST),run in capturemode and ineiastic mode (to obtain carbon/oxygendata), was run in each of the three observation weilson completion. The first, and to date only,carbcm/oxygen monitor pass was conducted on O-2,the weli where temperatureand neutron iogs showedsignificantanomaiies. Figure 24 shows the computedlog, inciuding iithology and saturations, around theintefvaiwherei-49 is compieted, Beiow900 MD,veryiittie =turation change has occurred, consideringthetoois statistical resolution of &5 saturation units.Above 900 there are s~verai intervais that haveexhibited measurable oil saturation increases,particularlythe intervai 855 to 890. This intewal isapproximately50abovethe projected course of 1-49s

weii path, but s weii within the depth intewai that hasexhibited the dramatictemperatureincrease.

nklQ 3

Monthiv iniection DataFigure25 showseach injection weiis monthlyaverageinjection rate and tubing pressure. Also shown arepseudo injectivities: IBWPD injected + tubingpressure. Note that injection rates in the horizontal

weii are very.simiiar to the verticai weiis. Pseudoinjectivity,however,is higher in 1-49than Intwo of theverticai welis, Assuming specific injectivity(BWPD/psi/ft) wouid be constant, this would indicatethat i-49 is injecting steam into a iarger (ionger)intervai, not surprising when one considers that withthe desaturated intervais and gravity override, theverticai injectors are probabiy effectively injecting


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Evaluation OF HOR ZONTAL,RADIALAND VERTICAL lNJECTION WELLS6 IN A PILOT STEAMFLOOD

1SPE24630

CONCLUSlONS

1

2.

3.

4.

5.

,

Ccmtlnuoussteam Injection into the horizontalvJeli has effected a rapid, localizedtemperaturerise in the intewal being targetedfor sweep improvement.

ThehorizontalwellpatternshaveexhibitedthesameIncreaseinwaterproduction,considereda precursor to incremental oi , as the threevertical well patterns. Steam oil ratio in thehorizontalgroup is half that in the verticalwell

group, indicating that Injection in thehorizontalwell is more effjclent.

Cyclic steam injection in the radial well hasresultedin pronouncedtemperatureincreasesIn a nearby observation well, matching theshape of the observatioriwelis resistlvitylogand indicating that the radiais are effectivelyfocusing steam in distinct vertical intewals.Consistent with the small amount of steam

injected,thlstemperaturecharacterdisappearswith time.

Two of the four offsetting producers haverespondedveryfavorabiyto the secondcyclesin the radialwell,

While severalwelis have shown increased oilproduction due to steam injection, pattern-wide production lrtcreas~sin the pilot areahavenot yet beenseen. The lack of response

s consistent with the time required before seeing ~

incremental oil In the older steamflood area of thelease,

ACKNOWLEDGEMENTS1

The a~hor would like to thank the management ofUnocalfor permissionto publish this paper. A speciai

thank you goes to Jennifer Mattisonand Ray Nemetzwho preparedthis manuscript for publication.

REFERENCES{

1.

2.

Llvlngston,N. D., Qulntana,J, M., and Buller,S. M,: Unocals Horizontal and Radial Pilotinjectors In the Midway Sunset Fieldt paperpresented at the San Joaquln .Geologi@Societys Symposium on Ap@lcations ofHorizontal Drilling Techniques, Sakersfleld, ,June 9, 1992,Nees, J., et al.: An Innovative DrillingSystem, Final Repoti for Contract No. DE-

DOE/BC/14203-4, May 1991.3. Dickinson, W,, et al.: Horizontal Radiais

Enhance Oil Production from a Therm~Project,Oil &Gas Journal (May4, 1992),116-124.

4. Dickinson, W,, et al,: Fiexible Sand Barrier(FSB): A Novef Sand Controi System,paperSPE 18787 presented at the 1989 SPECaliforniaRegional Meetinq,Bakersfield,APrii

Table1- Reservoir Data

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Documents

SPE-24630 Evaluation of Horizontal