Integrated study of the Kraka Field - 23082.pdf

7/27/2019 Integrated study of the Kraka Field - 23082.pdf

1/14

SPESPE 23082

. .

Integrated Study of the Kraka FieldL,N, J qrgensen and P.M Andersen, Maersk Ol i eog Gas ASSF: Members

Copyrqh l 199!. SocmuyJ PoIro Ioum Cnomool$. I IICThm paper wasp!cpafoc ! for prosonlal ,on d !hc Ollshorc Curopo Cunfomnce Iho ldm Afmrduon, 3.4 Soplombor 1991Thu paper was Wloclod !01plosonlmln by m! SPE Program Comnmloc Iol lowmq rovmw of mlo ln la !,on Conla(nod In an nbs lfac l Sut,mdlOd by lho iwlhotls) Conlanls of 1110paper.ii!! P1OSIIOIOU,hnvo nol boon 10VIOKC.3by Ihc Soc!o!y of Po!roluultl EnQ!noOr9and aro subIecl 10CWWC!IOI1by !I1omImcqsI. Tho matcrKd, a~ proson!od, doos no! n.xcssar$ly rollcc!any pos,l ton of Iho SOCIO!Y01PoIrolmIm Engmccrs, IISolf,ccrs. or mombofs PIWUISprcscnloil al SPE mcohng$ two SUIIICCI10IIublicaIIon mwcw by MI!OWII Comnllttccs 01ma SOcmly0! Pmmlou!n Engmow8 Pcm11s5101110opv ISKistmcd !0m C! I>5 I1OCI1nol II1OO2han 3CQwotd~ Illuslfaltons may I1O!be copIod TIIOabs!tnc! should Conla(nConspicuous acknowlodgmcnlof whwo ml by WIICMTI! lQ paper ISpfow !n lod WtI lo L lb !a ttm SPE, P O I lox 033836, ! lc ha ldsm TX ? .%3033836 US A To lox, 730989 SPEDAL,

The rwwvoi r rock I s a f racturedchaI kof Dani anandMaastri chtanage (equi val entsf theEkof i skandTorA8STWT formati ons) .hebul kof the011i strappedntheDanI anTheKrakaFi eld,di scoveredn1966,was thef trst ot1 chal k,whi chcanbesubdi vi dedntoanupperporousanda l ower ti hter i nterval .The reservoi r contai nsdi scovery ntheNorthSea. Thef i eld,a l argeel ongated !aturatedoi underl yi ng srral gas cap. The ini ti a1chal kstr ucture, s l ocated nthesouthernpartof theCentra1Troughi ntheDani shsectorof theNort hSea. reservoi r rt !ssuret thegas-oi1 contacti s 3640psi a!25000kPa . Ori gi naloi l - i n- pl acentheareal l yl argeTheKrakafi el di s characteri zedy a l owperr rs?abi! ty structuresesti mstedobesore500m11 onbarrel s(80ml l tonm3) .mst ri xYJ ih some enhancementof perrneabii ty due tonatural fracturi ng,The fl ui d di stri buti on ;] the TheKrakafi el di soperatedby Fl wsk01i eog GasAS onreservoi r scorpl ex.Throughouthehydrocarboneari ng behal fof theDUC(Dani shUndergroundonsort{rn)whi chzone,mr i x water saturati onsarc i nexcessof 50% i sa partnershi petweenA, P. MB1 er, Shel1andTexaco,Fl ui dcontactsare ti l ted,then% ri xoi 1watercontactdue to tectoni csand thef racture reewaterl eveldue FIELDHISTORYto a regi onal hydrodynamcgradi ent, Vari ati onsi npressuresand fI u d propert os further add to the TheKrakafi el dwasd{sco~erodn1966andwast hefi rstCol rpl exi tyf t hef i el d. oi 1 di scoveryi n the North Sea (the Anne f i nd) .Ref l ecti onei smchaddef i neda nunberof str ucturalThi sr)aperdescri besan i ntcgr. ?t cdtudycf theKrakaf i el d.Tho i ntegrati onf a geol ogi calf racturestudy cl osuresat several strati graphl c evel s, and thedi scoveryWC11,A- I X, wasdri1l edto testoneof thesew th a reservoi rsi nw ati onstudyhas resul tedtn an structures,i mprovedetervor characterzat on,Thedevcl opnsmhi storyof t i l etol dd?nw ]stratesownew Of1and as showswererecordedw mnthewe11penetratediopchaI . Dri11ngoporatonshadtobc suspondcd0fttechnol ogycanprovotethedevel opmentof a awgi ns1 (25m i ntothechal kafterseverewel1controlprobl ems,fi el d, Thewel l wasdrt l l cdw tha dri l l shi punabl etooperateI HTFWUCTI OH under w nter condi ti onsi n the North Sea, Due toworscnl ngof weather condl t ons and wel1 contr olTheKrakaf iol di s I ocatodnthesouthwostcrnornerof y$b; cnrs,the welI was pl ug~cdand abandonedboforcthoDani shNort hSeasector,127ml GS(205kmwestof g ri gandtesti ng.theportofEsbj ergnd5, 6ml es(9km southof ttmDan Theoi l andgasshowsrecordednA-1Xweresuccessful l yFi eld(Fi gure1), testedthesucceedi ngearby thetw nWC11A- 2X,OnaGeol ogi cal l y,hefi el di sst tuatcdnthesouthernpart shortoi1 zonetest thi swcl1 producedup to !2900l OPD(460ma/ d).A-2X,however,cncountcrcdatersaturat i onsof theNorthScaCentralTrough,Tho trapi s a sfnpl c i ncxccssof 504 i ntheenti reoi l col umn,Thehi ghri skstructuraldornow ngi tscxi stoncctothef ornwti onf of earl ywaterbreakthroughwas reali zcdand theAnnoa sa)tpi l l owof UpperPerm anage, Thesal t pi ll owi s f i ndwas cons dcredcconomcall ymargi na, and furtherpart of a trendof hal okincti ct ructuresknownas the Southernal tDonx?Prov!nce(Fi gure1). apprasa waspostponedor nearl ytwodecades.I n1984,t heapr ai salwel l Anne-3(A-3)wasdri l l edon1he southernf ank of the fi el d,whrm a ti l tckcri 1Rcf crenccsand i Il ustrati onst ondof paper, col umn was encountered.A- 3 thus provi ded someencouragement,and i n 1. 985the fi el dwas decl ared

461


2/14

2 I Pi TEGRATEDSTUDY OF THE KRAKA FI ELD SPE 23082conmcf al ,Economcswere, however,st{1I margi nal ,I n thesucceedi ngears,Mersk01i eogGasAS success.fu1I ydri1l edseveralhori zontalwel1s i nthenearbyDanFi el d*, Hori zontal wel1s appearedattraci ve fordevel oi ngand i nprovi ngheproducti vi tyt the l ow1err rea1i ty, areall y l argeand thinoi1 zone i n theKrakaf i el d.I n l WB, work was i ni ti atedto devel op l ow costfaci l i ti esor sml n~rgi nal f i el dsl i kethe Krakaf i el d,Thi seff ortresul tednthedevel oprm?ntf theso-cal l edSTARpl atf ormS1 mTri podAdaptedtoRi g) . TheSTARplatformsare-usabl e,mni mumaci1it i espl atf ormthutcanbe tnstal edby a j ack- upri g3,Dri venby thesetechnol ogi calachi evements, stepw sedevel opmentf theKrakaf i el dwas i ni t i atedn1989w ththedri1l i ngof thetwof i rstdevel opmentwel1sA-4andA- 5. Thesewel l s, i naddi ti onto thei rpri rr nbj ecti veas oi1 producers,al socarr i eda nuti erof appra{salobj ectves.A- 4wasdri Il edasa conventi onaldevi atedwel1cl osetoA- 2Xi nordertoconf i rmherel ati vel yi ghproducti vi tyof thi s ari +aand throughprol ongedtesti ngprovi detnformst i onegardingwaterandgasconi ng.Thetesti ngof A- 4showedrapi dgasandwaterencroachrmmhowngthat oi l producti vi tywoul d be i nsuff i cientfor aconmmci alf i el ddevel opwstw thconventi onalwel l s.A-4was theref oreubsequentl yi detrackedohorizonta1.A- 5was l ocatedon thenortheasternl anki norder toapprai setheextentof theareaof goodproducti vi ty.Basedonexperi enceromA-4, thewel1wasdri1l edas ahori zontalwel1.Testi ngof the hori zontalwel1s provi dedsuf f i ci entencouragementoenbarkuponthenext stepof devel op-ment;namel ya l ongtermreducti onestf romamni mum[aci l i t i esTARpl atf ormFi gure2) w thproducedl ui dsbeing, ?vacuatedhrougha nul ti - phasef l owIi net o theOanprocessfaci l i t i es.TheKrakdSTARpl atf ormwas i nstal l edn l ate1989andproducti onornmncednApri l 1991at ani ni t i alrateofsom 4000BOPD(635ma/ d).RESERWRDESCRIPTIONTheKrakaf i el di s a l owrel i ef ,~real l yl argedomalstructureontai ni t l gaturatedi 1 i nl owpernk?abii ty,hi ghporosi tychai !


3/14

SPE 23082 L. ) ( , J ORGENSEN AND P.M ANDERSEN 3presencef a natura f ractureystemtwasevi dentthatrapi dconi ngof bothgasandwaterwoul dresul ti nveryl oweffect~ve0{1product vi tyf roma verttcalwel l .The A-5 wel1 l ocatedon the nort heasternl ankwassubsequentl yri l l edasa hori zontalwel l . I ni ti al l y,api l ot hol e was dr.1l ed to determne saturati ondi st rl butonandf l ui dcontact sandassessthedegreeofnaturalfracturi ng.The2000ft (600m l onghorfzonta1secti ondri1l edi n theupper part of the01 reservoi runi twascompl etedw tha 400 f t (120m sl otted1i neri n the di stal part and four 200 ft (60 m sets ofperforati onsquall Yspacedal ongtheproxi mslpart.Thewel1wastestedfortwoweeksat oi I ratesof VPto5000BOPD(800m3/d),After4 days, theproduci ngGORbeganto ri seandeventual y reachedsome2000SCF/STB(350m3/m3),Awatercut devel opedaf ter6 daysr eachi ngsome10%by theendof thetest (Fi gure6). Theproducti vi typri ortoshut- i nwas12B/ D/ PSI(0.28m/d/kPa),sometenti mesthe f i nal PI measuredduri ngtesti ngof theA-4wel1. Aproducti onoggi ngool (PLT)i ndi catedhatthethree nm proxi mal perforatons were the mai ncontr i butorso f l owBasedon theencouragermntromthetesti ngof A- 5, A-4 was si det. reckedo hori zontaandcompl etedw th17perf oratedi ntervti l s.- 4 hori zontalal so i ni ti al l yf l owedoi1 at ratesof around5000BOPD(800m3/d)butexperi encedn earl ywatercut associ atedw th; rapi ddecl i ne noi 1r ate,At oi1r atesof 2000BOPD(320m3/d)thewatercutwas j ustabove20%TheGORi ncreasedra-dualI y approachi ng000SCF/ ST13350m3/m3)by theendof the testingperi od(Figure7), The fi nal PI ofapproximatel yB/ O/ PSI(0,12m3/(d.kPa)) ,was somewhatdi sappoi ntng when comparedto A-5. A PLT surveyi ndi catedhatonl ytheproxi rmperforati onsontri butedtof l owi !atri xl utdDi str i buti onTheoi l col umni nKrakai sup to 225f t (70m hi gh, l ti scharacteri zedy veryhi ghmatri xwatersaturati onsthroughout,eneral1y i nexcessof 50%Overl yi ngheoi1col umni sa smal l gas capw tha hei ghtof l essthan25f t ( 8m .Thehighwatersaturati onspl acetheenti reoi l col umni nwhat reseti l esthe transi t i ononebetweenoi1 andwater nth~nearbyDanf i el d.At Oan, i t hasbeenfoundthatthehighwatersaturati onsn thetransi ti ononegi veri setoveryl owef fecti veoi l permeabi lti es,TheDanf i el di sonl ynatural l yr acturedoa very1i mteddegree, and the exi stenceof f racturesat Kraka i sthereforethe si ngl ermst i nport antprerequi si teoreconomcoi I recoveryf romwhatwouI dotherw sebe anunproducti veeservoi r.Thematr i xoi l -watercontact( the100%Sw l evel ) i nKrakai s t iIt ed, To adequatel ymp theOWCacrossthef i el di t i snecessaryotakei ntoaccountthechangei ndepthof the OWC causedby porosi tyand pern~abi1it yvari ati ons,Theresul t ngSI i ghtl ycurvedsurfacedi ps0, 8degreestowardsthesouthwest ,Thi si sal rmstexactl ythesati ni recti onas that of a l ateTert i arytectoni cti I tseenonsci smcthroughouthesouthernpartof theContra]Trough,Thi s tectoni ct iI t i wmuntsto 0. 7de-grees,I t i s thereforei kel ythat theti ItedOWC i saresul tof tectoni cnovcnwnt,heprobabl eeasonforthel ackof re-equi l i brati onstheveryI owoi l - permeabi l i tyneartheoi 1-watercontact,Theobserved100%Swl eveli shencea frozenpaI co-OHC.Theobservedvari ati onnthefi ol dw deOWCcenterstheoi1accumul ati onomewhattothesoutheastof thecrestof thestructureroundtheA- 3wel l ,l hc 1004 Sw l evel i s al soti l tedi n thenearbyDanf i el d,Thedi recti onf theti l t i st hesaImas i nKrakai nagrm cnt w th theregi ons1 tectoni cti i t di scussedabove,Thecross .sect ion shown i nFi gurc8 suggeststhat

Krakawas chargedw thhydrocarbonsas a resul tof aspi l l - overf romDan, Thi s may al sOexpl ai nwhy thecrestalareasi nKrakaappearto be ti ghterthf i nnthecorrespondngareasinDan( porosi ty34%aso posedtoi40%i nDan) . Krakawas si mplychargedmuch ater andf i r&s tyreducingdi agenesscouldcenti nuefora l onger.StattcPressuresndFracturem WaterLevelVari ati onsRFT pressuresf romA-3, A-4 and A-5 i ndi catestati cpressurevari ati ons(Figure9) , Water zonepressurescl earl yshowateralvari ati onf upt o30psi (200kPa) ,Thi s pressuretrendcan be expl ai nedby a regi onalhydrodynamcradi entresul t ngi na ti It of thef racturef reewater l evel (FWL)towardsthe southeastw ththedeepestFWLbeingfoundi nA-3.Theexi stencef ahydrodynamcradcnti nthechal khasbeenestabl i shedhroughoutheDani shCentralTrough,Thi sgradi enti sbcli evedtobea resul tof deeperburi aland strongercorrpacti onof the cha1k towardsthenorthwesti n theCentralTrough.Thenngni tudeof thegradi enti s some0,003psi / f t(0.07kPaim,The stati c oi 1 zone pressuresare scatt eredbut i fi nterpreteds i ndi catednFigure9an i ni ti alreservoi rpressureat the GOCof 3640psi a (25000kPa) canbei nferr ed.The vari at i on n FWL i s al sosupport edby producti onteStS. Thewater zonetest i nA- 2X, cl oseto theFWLi nferr edromtheA- 4RFTs,producedwaterwhereastheMaastri chti ani 1zonetestsi nA-3at approximatel yhesarmdepthi ni ti al l yreducedsmeoi 1, i nterpretedoYri gi nate romoi1 fi l edfractures.Theresul ti ngdi str i buti onf thehydrocarbons,w thasouthwesterl yi ppi ngmatr i xOWC and a southeasterl ydi ppi ngFWL i s iI l ustratcd n the east-westcross-secti onshowni nFi gure10.

FMd PropertyVari ati onsThef l ui dproperti eseri vedromnalysi sof f l ui dsf romthe di ff erent Kraka wel1s show SOM signi fi cantvari ati ons.Theoi1 f romA-3wos undersaturatedw tha saturati onressureof 2$50psi a(20000kPa)sore700psi (5000kPa)bel owthei ni t i alreservoi rpressureat theGOCof 3640psi a( 25000


4/14

4 I NTEGRATED STUDY OF TH[ KRAKA FIELD SPE 23082

perrreabiit i esarevery l owovernm of thesaturatonrange.Averageresi duaoi1saturat i onsarybetween30and50%w ththeDl,themai noi l zone,havingresi dualo{1 saturati onsn therangeof 30 to 40 % I f theseresi dualsaturatonsare representati vef reservoi rcond{tonsi nKrakathenthenmvabl eoi1volurresveryI {mtedandessenti al l yest~ctedto theI Nof1 zone.FRACTURESTUDYThe nature (type, s{ze and ori entati on)of naturalf ractures1n the Krakareservoi rhas beenstudi edoncoresand FMS recordsfromA-4 andA-5. I n addf t i on,theSHDTrecordf romheA- 3wel1hasal sobeenanal ysedi nanatt enpttomapf racturesandsrnal scal efaul ts,Natura f ractureshavebeenobservedoncoresfromKrakabut w than i ntensi tymuch l owe~ than i n the nearbySkj ol d,Rol f andDagmarf i el ds12 1Fractureh~OrfOSThefracturesoccurri ng1nKrakamsybegrouped ntothefol l owngenetI ca1l yseparatecategori es:Styl ol! teassoci atedracturesStyl ol{te associ atedf racturesare bel i evedto beextensi onracturesderi vedf romthesameconpressvestateof stressas the styl ol i tes4 $5,n Kraka, theyaregeneral l y essthan:.i nch(25rnn)centi metersi ghand l ess than 0. 02 i rl ch(0. 5 mn) wtde, they aros!i bvertca1 and i nnm i nstancespropagateawayf romthe ti psbf styl oli tes.On Krakatheyhaveonl ybeenobserved n 1i mtednumbersandappudr to be far l essabundantthanthetectoni c racturesdi scussedbel owI thasnot, therefore,beenPOSS bl etomaptheregi onalvari l l toni ntheori entati onf thesef ractures,Heal edhai rl i nef racturesThehatrl inef racturesareveryconsmni nnm reservoi runi tsof theKrakachal k.Theyarec. onpl etelyeal edbycal citI ccementandappeartohavea l owerporosi tyandpermabi1i tythanthesurroundi ngmst ri x,andhencedonot enhance reservoi r pernw bi1i ty. The hai r l i nef racturesoftenformanastomosngnetworks.Al thoughdomlatedby conj ugateshear f ractures,extensi onalccsr fsonentsre f requentl ypresent.Core and outcropobservati onsi ndi catethat thesef ractureswereforrw ?deryearl yi nthehi storyof therock.Thei mport ancef thi sI st hat thefracturesoul dbe the resu1t of a stress fi el dother than thoseassoci atedw th the domngprocess.Thi s coul dbe aregi onalstressf i el ddomnantbeforethedomngtookpace.I nKraka,hai rl i neractureshavei ndeedbeenfoundtohavea comnonE-Hor~entatonthroughoutthef i el d,Tectoni c racturesThi scategoryI s by far themost l ~ort ant i ntermsofcontrtbut~ontoreservoi rpermeabiity, Thesef racturesareconsi deredobe rel atedto thedomngprocessandare fori rs?dateenoughi n thehi storyof therocktoal l owsomeof themtoremi nopentoday.Bothshearandextensi onomponentsaraobserved.Therel ati onshi petweenthel ocalstressf i el dandtheresul tngf rdcturesi s wel1 c tablishedf romf racture?theoryand l aboratoryestsl o. Shear f racturesformparalI elt ot hei ntermedi ateri nci palstressatanacuteangl eto themximumpr~nci palstressaxi s. The shearfr acturesformconj ugatesets gi vi ng ri se to twopotenta1shearf racturedrectons,Extensonf racturesformperpendi cul arto the mni mumstressdi recti on,Extensi onracturesmayor maynot beopenat reservoi rcondi t i ons,whereasshear f racturesoftonare i nter-pretedtobccl osedi nthereservoi randtor estr i ctf l ow

ort hogonalto thef racturepl ane,Hhickof thesethreef racturedi recti onstwoshearsandoneextensi on)redevel opedli11varydependi ngnl ocalcondi tms. Theextensi onractureypei stho@ tobeasi gni fcantcontri butorotheperrwabi1i tyenhancementobservedn Kraka. Inthepresentworkshear f ractureshavebeengroupedtogetherw thextensonfracturesorthe si npl ereasonthat the nunberof f r~ctureswhi chcoul dposi ti vel yei denti f i edsextensi onractureswasi nsuff i ci entor stati sti caltreatment,During thedomngprocesstheKrakachal kwassubj ectedto boththeregi ons1 stresssystemesponsi bl eor theformati onf thechal kdom andassoci atedocalstresssystemsgeneratedw{thinthechal kduri ngthedomngprocess,Thi sr esul tedi na videvari etyof potenti alf racturedi rect ons.i i owever,tearns(~nNel son17)defi netwomainf racturePatt ernsassoci atedw thfol di ng.Ona domethesew1Ibeexpressedsaradi alfractureystemndatanenti a1- -+ractureystem- racture typesmakeupnear~si gni f i cantracturesona domandareby far thenmPredi ctabl ef the fol di ngassoci atedractures.Each~ystemconsi sts of two- conj ugateshear f racturedi rectonsandoneextensi onracturedi recton.Urfentatl onf TectontcFracturesFractureori entati onataI rrKrakacomefroma numberofsources,Ori entedcoreswereavai l abl eromA-4andA-5, I nadditi on,conventonalcoresf romA- 3,A-4andA-5, whi ch coul dbe ori entedassumngbeddi ngto beparal l elto thestructuraldi pobservedonsei sm c,wereal sotncl uded.A3-armdi pmeterrecordf romA-2anda 4-armdi pmeter(SNDT)r ecordfromA- 3wereprocessed1nordertodoa str ucturalanal ysi s.Thi sanal ysi sdtdnotrevea1 any di rect informatonabout f racturi ng,butenabl eda mappi ngof faul tsanddragf o?dsassoci atedw thfaul ts,Fi nall ya Formati onMcroScannerl og(FMS)was runi nt hepi l othol eso; bothA-4andA- 5.The i nformati onobtai ned f rom these sources aresummi sedtntherosedi agramsshowntnFi gure11.Ascanbe seenthereare numerousexanpl esof f ractureswhi charesubparalelw ththecontoursof thedonw I rrA-4, twod}rectonsaysedr to be present.There i s apossi b{i ty that these are representati veof theconj ugatehearcowonentsof thesanx?ractureystemThecorrespondngextensi ono~onentwoul dbeori entedpar alel to thecontours.Soreof theNNE-SWori entedf racturesi n the A- 4 cores were i ndeedextensi onf ractures.I n termsof thef racturessystemsdi scussedabove,theabundantcontourparal l elf racturesmsy be i nterpretedas tangenta1 systems.Thereare obvi ousl ya cert afr rproport i onof the f ractureswhfchare not tangenti al ,Someof these(fnA-5andpossi bl y nA-4. )areradi al .I n concl usi on,therefore,tectoni cf racturi ng n thoKrakachal k,maybc understoods shnf sl eomerel atedf ractures,poss{bl ydomnatedbya tangental systemTt!cwel1s are l ocated i n three diff ercrrtstructuraposl t{ons:near crestal( A- 4) , i rr ternwdi ateA- 5)andf l ank (A-3) . I t nksythereforebe assumedthat thetangental f racturesoccur across the enti redoro,al thoughnotevenl ydi stri buted.l ateralVarf atl onnFracture nterdtyFromoutcropobservati ons t i s knowthat f racturesrarel y are evenl y di stri butedl atoral l +. I n theLaergcrdorfhal kquarryinNorthernGermany ,whi chi sl ocatedona sa1t i nducedstructure,f racturesoccurI nswarmsrather thanat constanttntervas evenwherobeddfng spl anar.Unfort unatel y,odi rectobservati onspertai ni ngothel ateravto i atoni nf racturentens~ty

.

464


5/14

SPE 23082 L.F!, J ORGENSEN AND P.M ANDERSEN 5are avai l abl ei n Kraka, An FMS tool was run fn thehori zontalhol eof A-5. However,due to di f f i cul ti esrel atedto errat i ctool nmvement,processi ngof therecordresul ted nnomeaningfuli mages.I i owever,one pi eceof i nformati onmay i ndi catethatf racturesa1sooccuri nswarmsi nKraka:ThePLT,runwhi l etest i ngthehori zontalsecti onof A-4, i ndi catedhatonl y4of the17perf ol aton1nterval si nt hewel1 contr i buted4%of thef l ui dproducti on.Thesefourperforati onsrecoi nci dentw thl evel swherethecal i pershowsi ncreasedhol esi ze,andat thesannti rmheresi sti vi tyncreases.Thehi ghr, resi sti vi ti esarenotaccompani edyanyi ncreasen Forosi tyaswoul dbe expectedi f thehi gherresi sti vi t i ~sesul tedf romhrprovedmstri xoi1saturati on.Al ternatvel y,thehigherresisti vi tymy resul t froma swarmof oi l f i l l edf racturesrossi ngheW?lbore,thusexpl ai ni nghehi ghproductonfromtheperf orati onst thesel evel s.A sim l ar compari sonof resi sti vi ty/hol ei ze w thproducti vi tysnot possi bl ef romhePLTruni ntheA-5wel1, becausetheperf oratednterval sresol ongthati t i s i mpossi bl eodetermnaexact l yf romwheretheoi1producti onri gi nates.Theaboveapproachi s not consi deredmore thana vel - yi nd{rectndi cati onf naturalfr acturi ngndshoul dnotbeusedasa f racturei ndi ngtool ,However,i t gi vesan i ndi cati onf the spati ngbetweenthosefr actureswhi chcontri buteto f l ui dproducti on.Basedon theobservati ons n A- 4, a spaci ngbetweenthe f ractureswarmsof 100 to 500 ft (30 to 150m i s consideredl i kel y.Thi s MSY, i n turn, expl ai nthe di ff erencei n testperformanceetweenhehori zontalwel1sA- 4andA- 5.Theobservedari ati onmaysi npl ybea functi onf thenuti erof f ractureswarmsi ntersectedy the i ndi vi dualwel1.I naddi t i on,therel ati vel yowpermeabi1i tyenhancementobservednA- 3asconparedoA- 2andtheA-4pil othol econf i rmhe l ateralvariati oni nf racture ntensi ty.Vert i calVarl attonnFracture ntansWyApartf romhecoreandFMSrecordsanSDTrecord(ful1waveformoni c)wasacqui red nthepi l otholesof bothA- 4andA- 5. For thepurposeof f racturedetecti on,aspeci alprocessng (STFRAC)was carri edout on bothrecords.Thi s processng usesthedi rectand i ndi rectStonel eywavearri va1stoconputethel ocati onf crackscrossngtheborehol e.Therei sa bett ercorr el at i onf coredataw ththeFHSdatathanw tht hevari at i onntheStonel eyef l ecti oncoeff i ci ent.uhenoverf racturesare presenttheyarcencounterednal1 reservoi runi ts i n thehydrocarbonzone as wel1 as i n the underl yi ngwaterl eg, I nparti cul ar,t he upper part of theD2 uni t di spl aysastrong racturentensi tyothonFMSandcoredata.Thi smayresul tfr omthefactthatt hi s i sa zoneof f requent1i thol ogyontrastsandof general Y l owducti1i ty,Producti onesti ngi n theverti calwel1s A- 2XandA- 3conf i rmomedegreeof f racturi ngna11reservoi runi ts,SIHULATIfJfiTIKWThe data obtai nedf romthe Krakawel1s compri seaconpli catedpi cturew th respect to many i~f)rtdntparameters,Thekey arametersaremri x andfractureontri buti on,!omnat ng f l owpatt ernsand the propert i esof thef racturesystemOnl y 1i mtedi nformati onbout theseparamerscanbe i nferredromthedata,andthereforea numeri calsi ngl ewel1 studywas undert akenn orderto i mprovehedescri pt i onf theKrakareservoi randi n

part i cul arurthercharacteri zehef racturesystemA-4Stngl eHel l ModelA threephaseradi aldualporosi tymodelwasconstructedof the A- 4pi l ot hol e usi ng the FRAGORreservoi rsi mator e.FRAGORwas sel ecteddue to i tscapabi1i tytosi nul atef racturedeservoi rsndmodelal1thedri vemchani sms i rrportant n Kraka, narmy capi1l aryi ntzi bi ti on,ravi tydrai nageandvi scousdi spl acement.A radi al , 16 l ayer nmdel was sel ucted.The mstri xpropert i esre showni nTabl e1.A 1inearcapi1l arypressureel ati onshipasadopted norder tomatchthetransi t i ononesaturati onprof i l ederi vedf rom ogs.I ni ti al1.vf racturepropert i eswere sel ectedbasedonpressuretransi entanal ysi sand i nformati onromcoresandtheFMSl og.Accordingl y f racturepermzabi1i tyofsome10TD (0. 01I@ was sel ectedand thedomnati ngvert i calf racturedi rect i onmodell edbysel ecti ngl owerhori zontalf racturepermeabi1i ty.Fracturepermeabi1ity, as wel1 as fr actureporosi ty,f ractureel at veperrnzabii ti es,f ractureo~ressi bi1i -ty andt hematr i xbl ocksi zewere themai nsensi t i vi typarametersvari edi nordertoobtai na hi storymatch.A- 4Producti onest Hi storytkstchTheA- 4pilot hol ewasperf oratedel owtheGOCi ntheDani anoi l zone. An earl y i ncreasein GOR and acorrespondi ngec1i nei noi1ratewasencountered.Af tersome3 daysa watercut devel opedFi gure5). Al 1 f l owperi odsarecharacteri zedydecreasngbottomol efl o-wtngpressuresassoci atedw thdecl i ni ngoi1 ratesandi ncreasi ngORS,Themstchof oi1 rateperformancewas obtai nedw thaf racturesystemcharacteri zedy a rel ati vel yhi ghconpressi bii tyanda pressuresensi ti vepermeabi1i ty,These eff ects are nmst pronol tncedlose to theperf orati onsuet o theef fectof theaci dsti mul ati on,Haterencroachnx?ntasnstt chedyad u:. ingthe. vertcalf racturepernmbi1i tyandpor~si ty nt hel owerpart ofthe reservoi r (02 and ri l ). A sensi ti vi tystudyi nvestgatf~gtk i nrI uenceof thepressuresupportf romtk aqui f eri ndi catedhatwaterencroachrmprovi i ?. snearl yconpl etebasa1pressuresupport.Therethusseemstobea signi fi cantpressuresupportfromtheaqui fer,Gas producti onwas matchedby an adj ustmentof thef racturepermeabi1i ty i n the gas cap, I t was al sonecessaryto S1i ghtl ymodi fy the f racturegas-et1rel ati veermeabi l i tyosi mul taneousl ybstchasandoi lproduct i on.Thebest matchof ratesandpressuresareshowni nFi gures12and13.The resul t i ngcharacteri zati onf tht?f racturesystcmindfcatoshori zontal ermeabi1i ti esof between2 and3ni l(0. 002and0. 0031#) w tha f ractureporosi tyof 0. 5% Vert i cal f racturepernt?abiit y i s f rom1 t o3 ni l(0. 001to0. 003pz#) i ntheupper art of thereservoi rsecti on1)1)and25ni l(0. 025d) ~nthel owerpart (theD2 and the M ). Fracturepermab{1i ty cl oseto thewel l borei s tni t i al l yenhanced(20. 160ni l ,0. 02- 0, 15I U#) but decreasesrapi dl yas the ressuredrops. TheResul t ngf racturepropert i esares own i nTabl e2.Themodel resul tscl earl yi ndi catehat f l owi smainl yvert tcal ;encroachmentf gasandwateroccuri nghroughthef ractureystemw thvery Ii mtedhori zontal(i . e,radi al )contri buti on.Theperf ormancef theA- 4 pi l otwel1 i s i nagreerentw thandsupportsthef racturemdel.Theperf ormances

465


6/14

6 I NTEGRATED STUDY OF THE KRAKA FI ELD SPE 23082presumabl yhe resul tof thewe} bei ngl ocatednaswarmf vert i calf ractures.Therelati vel yi ghf racture Thecontr i buti onorecovery romexpansi onndsol uti onporosit yused i n the model can thus be j usti fi ed. gasdri veinthemstri xw 1I l argel ydependonthepres-However, the averagef ractureporosi tyi n Kraka i s suredropi , e. thedegreeof pressuresupportfr omthecons deredtobe at l easta factor10 l ower. aqui fer,Li kew se,as di scussedabove, the hori zontalwelIperf ormancebservi ?dnA- 4andA- 5 i smost 1i kely theresul tof thehorlzontalwel l borecutt i ngsevcraswarmsof verti ca f ractures.Themodel i ndi catestdtr i xontri buti onuri ngthetest.Rapi dexpansi onof matr i xof1 was foundto be theexpl anati onor thepeak i noi1 ratesat thebegi nni ngof each f l owperi od. The matchof thebui l dupal soconf i rmedhat the interporostyf l owaccountedor bya dual porosi tymodel i srequi rednordertomatchtheobservederf ormance.hemri x contri butonduri ngthetestwaspri mari Yduetot hepressuredi f ferenceetweenthe f racturesand thematr i xbl ocksandexpansi onofmri x f l ui dsas a resu}tof pressuredepl eti on.Onl yarel ati vel y1i mtedamount of f l ui ds was, however,producedromther rkstri xndt he testwas tooshort toprovi deinformatonregardirl gothermchani sms,ENU. YPRU)UCTIORPRFORMNCEAfter i nstal l ati onof the STAR pl atf ormproducti onccnsmncedr omKrakai nApri1 1991. I ni ti alYonl yA-5WSput onproduct i ont a rateof SOI I E000BOPD(320m3/ d) ,A- 5 i ni t i al l yproduceddry oi1 w th a graduali ncreasen theGOR(Fi gure14). Af tera weekA- 4wasalsoput on producti onand f{eldofftakeroseto 4000EOPD (640 m/ d). Short Y thereaft er,A- 5 startedproduci ngater.Af terthef i rstmonthof producti onothwel1swereproduci ngwaterandthef i el daveragewatercut hadreachedsome20% Bottomholepressuresaremeasuredcenti nuousl y nbothwel1s.Theearl yproduct i onerformancehuscl osel yresenblestheperfornvmcebserveduri ngtheini ti a1wel1testi ng,i ndi cati ng nme or l esscorqzl t?teechargingof thef racturesystemw thoi 1.Consi deri nghatthef racturesarepri nwo iysubvert i caland appear i n swat~.w th a rel ati vel ypoor l aterali nterconnectvity i t l i kel ythatt hemainsourceforrechargingsmatr i x01:Thefactthati nhi bi t i onhu.appearstohavebeenacti vei sencouragi ngut doesnot quanti f ytowhatextentthei nhi bi ti onf f i ci encyanbecoman i nport antmchani smfor sustainedoi 1 producton f romKraka. Addi t i onalproduct i onexperi encew 11be necessaryto proveanysi gni f i cantt i i bi t i onotenti al .The l ongertermwaterencroachment,ressuresupportandGORperformanceremaj orunknownsi nt hi srespect.Thehori zontalwel1saredri1l edi ntheupperD1oi1zonewhereaverageoi1saturati onsresome55% TheDl oi1zonehasa thi cknessof some60 to 70 f t (18t o 20m.I nthe02andM , watersaturati onsre i nexcessof 65%poi nti ngto a vi rtual l ackof mobi l eGi l i n thesel ayers,The targetnutri xoi l f or potenti ali nhi bi ti onrecoverysthusrestr i ctedoa verythi nri mofnwabl e$1 t~et~2enhehorizonta1welI traj ectori esndthetop.Asdemonstratednthesi ngl ewelI studyof theA-4pi l othol etestsi gni f i cantpressuregradi entscanoccural ongthef ractures.Thesegradi ents,whi charetheresul t01therel at i vel yow ractureerrceabii ty,exertadri vi ngforceon thematr i xbl ocksandtherebydi spl acemri xf l ui ds.Thi s vi scousdi spl acementcoul d, i f acti ve,resul t i n resi dual oi 1 saturati ons ower than thoseobtai nedromspontaneousmbibi t i onhusi ncreasi nghepotenti al movabl e oi 1 vol urm (negati vecapi l l aryprcssurcs)o

CONCLl i SiONThedevel opnmhi storyof theKrakafi el daspresentedabovedenmnst ratesownewtechnol ogy,hori zontalwel l sand l owcost faci l i ti es,may resul t i n corrrnarcialdevel oprmof a marginalf i el d,Thedevel opmentStrategy i nal l yadaptedfor theKrakaf i el dhasgradual yevol ved romtheexperi enceai ned.The i ntegrati onf the geol ogi calf racturestudyw thnumeri calrr ndel l i ngas greatl yenhancedthe under-standingof themai nfeaturesgoverni ngproduct i onromKraka.Krakai s characteri zedy a l owpermeabl ematri xw thhi ghw?. teraturati ons,hereservoi rhassorr~egreeofnatural f racturi ngdomnatedby subverti calf racturesappeari ng n swarms.Hori zontalwel l s dri l l edi n theupperpart of thethi noi l ri mhol di ngthenmvabl eoi lmay i l i tersecteweralof theseswarmsof f racturesandthusprovi deconmarci aloi l ratesandpossi bl yopti mzei ntsi bi ti onecovery.The l owcost STARpl atf ormhasreducedthe devel opmentcosts and therebythe , I ski nvol ved.The i ntegratedtudyhasprovi deda cl earer i ctureof1owreservoi rpropert i esaryacrossthef i el . Thel ar-gest oi l vol unm s l ocatedon thesoutheasternl ankaroundtheA- 3apprai salwel l .However,thegreatestuncertai nti esel atedothefuturedevel omantof theKrakaf i el dare thedegreeofmstri x1ontri uti ontooi l recovery,naturalwater i nf l ux romtheaqui f erandthel ongertermGORandi fORw formance.AUUi ONi . EOGEHEHTTheauthorsw shto expressthei rappreci ati ono theco~ani esi nD, , ni shndergroundonsortumA.P. Mol l er,Shel l andTexa. : o)orpermssi onopub}i shthi spaper,


7/14

.

SPE 23082 L, N. J ORGENsEN AND P.M ANDER5EN 7 b

1

2.

3,

4.

5,

6.

7.

8,

9.

10,

11.

12.

13.

14.

15.

16.

REFERENCEStl i chel sen.0. , 1982: Geol ow of the Dani sh 17. Nel son, R.A. , 1985: Geol og\ c Anal ysi s ofNatural YFracturedeservoi rs.Contri buti onsnCcntr a1 G~aben:Geo ogca1 $;rveyof Derwrark,Sec. W No. 8.Andersen,S; Aa.,Conl i n, J . i l . ,Fj eldgaard,K.andHansen,S.Aa. : Expl oi ti ngReservoi rsw thHori zontal Wel l s: the Mersk Experi ence.k~$ti erger Oi l f i el dRevi ewVol 2, No. 3, J ul y.Ei I ersen,C. , 1989:Desi gnof a STARPl atf ormforMarginalFi eldsintheDani shSectorof theNorthSea. Propri etaryJCReport .l . i eberkir d,. , Bang, I . , M kkel sen,N. , andNygaard,E., 1982: LateCretaceousandDani anLi l mstone.I nMchel sen,0, (cd, ) ,Geol ogyofthe Dani shCentral Graben: Geol ogi calSurv.Denmark,Ser. B, no. 8, p. 49-62.Nygaard,E., Li eberki nd,K. and Frykman,P.,1983:Sedimntol ogyandReservoi rPararrrXersftheChal kGroupi ntheDani shCentra1 Graben.Geol ogi eenM j nbouwa. 62, p. 177- 190.E@egan, C.E, & Scul l , B,J, , 1977: A proposedStandardithostratgraphiNommcl atureor. theCentra1andNorthavnNorthSea.Rep. I nst,Geol .Sci b, 0077{?5.Doyle,MC.&Conl i n,J .M , 1Q90:TheTyraFi el d.North Sea Ll i1 and Gas Reservoi rsI I . ThtiNorwegi anI nst i tuteof Technol ogyGrahamndTrotmsn).J Ergensen,L.N. , i n press: Dan Fi e?d, MPGTreati seof Petr ol eumeol ogy,Atl asof Oi 1andGas Fi elds.D Heur, H. , 1984: Porosi tyand HydrocarbonDi stri buti onntheNorthSeaChal kReservoi rs.Nal ai neati Petr ol . Geol ogy,vol . 1, p. 211-.D Heur,M , 1990:i destEkofi skFiel d- Norway,Central Graben, Nort hSea. MPG Treat seofPetroleumeol ogy,Atl asof Oi l andGasFi el ds,vol . I V, StructuralTraps Tectoni cand Non-tectoni cFol dTraps.Hurst,C. , 1983:Petroleumeol ogyof theGermFiel d,Dani shNorthSea. Geol ogi een! i i j nbouwno. 62, p. 157-168.Oen,P. MEngell - J ensen,M andBarcndregt,,A. ,1986: Skj ol df i el d, Oani shNort hSea. Earl yEval ust on of Oi 1 recovery throughHaterI nhi bi t i onnaFracturedeservoi r.Sot.Petrol ,Engi neers,SPE15569,11p.J enseni us,J . &Munksgaard,N.C. , 1989: LargeScal eI i otWater I l i gratonSystemsaroundSal tDi api rsi nt heDani shCentr alThroughandthei rI nyxi ctni l i genessof Chal kReservoi rs.Geochmet Cosmochi mActs, vol 53, pp. 79-88.Nel son,R.A. , 1981:Si gni f i cancef FractureSetsassoci atedw thStyl oli teZones.A4PGI l ulet i n,V. 65, p. 2417- 2425.Hatts,N.L. , 1983:M crofracturesnChal ksofAl buskj el1Fi el d,Norwegi anSectorof theNort hSea: Possi bl eOri gi nand Di str i buti on.Bul l ,AAPG, V. 67, pp. 201-234,Stearns,D.WandFri edman, l . ,1972:Reservoi rs

petr ol euhGaol ogy& Engi neeri ng,v, 1,Gul fPubl i shi ngo~any.18, Koestl er,A. G. & Ehrmsnn,WU. , 1986: Faul tPatternsntheCal careousOverburdenf aChal k

Di api r: Laegerdorf ,NH Germany.N. J b. Geol ,Pal eont.Mh. 555-569.190 Quandal l e,P. &Sabathi er, i C. , 1987:Typi calFeatures of a New Mul ti purposeReservoi rSi nul ator,SPE16007.

i nFracturedRock, AAPGMemoi r16, pp. 82- 100.

467


8/14

SPE 23082

Table 1 - A-4 single well model. Uatz:Lx properties-Layer Top AZ F%rosiiy Permai r Perm~]i ~Sw Formati on

({fubsea)fl) (red) (red)16 5s33 21 0.325 0 S5 0. 4 0. 45 D1315 5s54 : 3 0% 1.5 1. 0 0. 45 Di .14 5s67 1.3 0.325 0.85 0.4 0.45 Dlb13 58S1 13 0.325 085 0.: 0.45 Dlb12 5s94 5 0.325 0.s5 04 (!.05 DIb11 5S99 18 0.26 0.25 0.1 0.65 D2a10 5917 5 0.26 0.25 0.1 0.65 lx?a9 5922 10 026 0.25 0.1 0.65 D2a8 5932 15 026 0.25 0.I 0.65 D2a7 5947 21 0.26 0.25 0.1 0.65 D2a6 596s9 02.9 035 0.15 0.65 IY2b5 5%7 20 0.2s 035 0.15 0.65 D-A4 5997 30 0295 2.0 1.1 0.6s M3 6027 30 030 2.0 1.1 0.775 L42 6057 = 030 2.0 1.1 0.91 hf1 6145 100 030 20 1.1 1.0 M

Table 2 - A-4 single well model. Fracture properties.

Layer/cell 7 2 3 4 5 6-:1k-

16 H 28 2.s 2s 2.s 2.s 2.sv 1 1 1 J 1 1

15 H 2 2 2 2 2 2v ~ 2 ~ 2 2 2

14 H 2 2 2 2 2 2v ~ 2 2 2 2 2

13 H 150 IOG 50 30 12 2v 25 25 25 2 2 ~

11-IZ H S50 100 50 30 12 2v 25 25 25 25 25 25

10 H 150 100 5C 30 22 2v 50 50 50 25 25 25

9H 2 2 2 2 2 2v 25 2s 25 20 2 2

1-S H 2 2 2 2 2 2

.------- .....~EAu~. : . > . l /

Fig. 1 Regional map with the position of thef i aka f%el d i ndi cated.

.


9/14

L a $l?:Lq. 2 The STAR platfor~ usedfor tl-ie Kraka development.

Fig. 3 Kraka field. Depth stru:ture map atTop Chalk level.

DepthIPoro9i ty/ Saturati on Reservoi r(tvdSS) Units50% 25%

Fig- 4 Computer prccessea 10G fromthe A-4 well xith parosities and oilsaturations indicated.

5650

5900

5950

6000

ma~(D1;Oc

Op02

OpM1

!atrix OWC


10/14

- (i,it~.- WA,L ,- .3KU - --l \ -- --.. ._-dne

Xlwu . . .... . .+-$ .,,,,..---, I ,..$,:,,,,,,,,,, , . . i ! j j . .,,,,,,,,,,,g Xmm 1*-- {k ~,/,/ .hj ri f I#L- .,. ,:~e~,,,,.

I,(XM

WmU

0

2!2 qO w l(x) 120 t *O !mTIME SIN!% STARTFig. 5 A-4 pilot hole. lestnos. 1 and 2, sequence ofevents.

- - - - - - . ~/ - - -tmca

.

,.f,%-,r

\


11/14

,. SPE 23082

471

r 1


12/14

W2Q

WYJ

4W0

woc

U2LC

G40(

SPE 23082

.-, ...r --Jx6h Rb\

e00,

X2

Mat ri xOWC

472


13/14

,!

,

473


14/14

890

1LEGEND:400 - BHP SIMLI i . ATI SD+B}i PMEASURED

Fig, 13 Hi story matcl ? of pressures.

SPE 23082

I(C411,, [.:, . *5CFX

01 Hhll*W , . . :i;, , , ,, w *!CCMw m ,(?9

7m .

G\ KKwgJI >,> ,; j

~ w)e

g : (l+ ~ .!2.J ~; Q

5

: J

~ ,(,. ?m :

ml, w , tam

!Iwl,. , .-..,----. 20 , 1(7M.,. .,.. --, .,.lwc , ,-- ..-.. 10 , X0

,-----61 . . . --------0 10 ?0 ?060D:YS PROMPR&lUCTION ST:T 10 w

S?ig. 14 Kraka field production performance.

Integrated study of the Kraka Field - 23082.pdf

Documents