m.-Sodety of PetroleumEngineers _.. ., .SPE 28714

Akal Field (Cantarell Complex) Conditions of Exploration, Analysis,and PredictionA.G.Rojas and A.R. Tomes, Petro[eos Mexlcsnos.SPE Member

Cwww $w Socw 0!petroleumEnglmrs,Inc.Thiswar tifiii.d 10,Pcea-ntatinn al the 3PE 1,,,.,(..! P81;lEum.@nf6?mc9 & ExhlbtUco of M&lw ,,[6 [ Vefaauz, Mexloe, W-13 CCW5W 1994.This paper .8s Wectec for presentation by a. 8PE Program Camm!& Ialiwing mviwaf [km!bn .wn$aln6d In an abs!rati Sibmlwd by the wtiorls], C4ntets 01 lha paw,as presented, hw @ been @vkued @ tha Sod@Iy o! Petroleum En@wwu and am suwt to CWWIICO by th. aiiWI@). The mateial, ai wsented, .dcss not nscassrilY vflectw PoatUmI.t tie SQCkaty.x%-m En@nws, ii%amews, w mwws. PaPms SJffimwd e.tSPE mwwa am wbjaol to FC41kaikc mvw w Edhmid cmrmnws a lh. Scdmy.1Pettiwn EDgineem Pwmiaion 10ccw ISrewrded 1. an ebs+rad of not MS mm 3c4 wwds. Iltiam!bn. may noms cwded. The aE6!naa shou~ wntal. mnsoiwus Xtiovdndgment01 where and by whom lha w., k Presented. W,it. Llbrsrl.w SPC P.O. %3x WSB6, FJch81dSO%TX 75C#W3W6, U.S.A. Telex 1SS245 SPE!JT.

SAEsmA c.

This paper pisserits a dctsiled description of .!lr~ currentconditbrs of exploitations in the &al Field (the most m@murrprcducer in Ca@eche So.d aud M&ico Co.firy].

The AM field, naturally fractured reservoir, began hisexploitation in jurie/79 wiilr ttie well Akal- 1A and 34,000 BOPDof production about 22 API. The field development wssgadm.lly and i @._tiddle of 198&d &l producer wei~, .nOWthe field counts wirh 140 wells and 890,000 BCIPD of productionwith 7500 BOPD per well in aveFage and cumulative productionof 4647 MMSTB; thus we can cltiiify like supergiant reservoir.

This field hm a gocd condition. for the gravity draimgemechmisms like thickness about 23Wl feet, high permeabilitymound of 3-4 Darcy and top reliev about of 60.COf&t.

It-s important to menticir that ibis field has a g&&p wbic&h-wbeen incmssing from 1981, now it risy/94 the @s-oil contact isat 5719 feet and we establish a continuos monitoring with TOTlogs. Based in this monitoring is possible to pr.dct workoverand fecomennd infiil - drilling.

FinsOy, we show the match snd predictioii behavior of the gss-.oil contsct through the time and different Gplotation alt.einativesdone with volumetic model.

G...++ _.....,,,References and illustrations at end of paper

I.mtroduction I

The AM field lies within the Cantarell Complex, Iccated 49.7mines northwest of Ciudad del f&rneq in .tbe GrrIf of Mexico,Figure 1. Thk field has one of the highest daily and cumulativepmdmtion records and is vw important to the overall Mexicanoil production.

The AM reservoir shycture consists of sn ssymme.hic snticliie..~e snticline isbound&fOn the west by a normal faul~) snd byan inverse fault on the orthem snd eastern sides. The soatb ofthe ariticlirte is a low porosity and low permeability region whichis lititcd by sn water-oil centact, Figure Z

The formation is natudy tlacbxed. The se.mndsry w@aIporosity is inter-connected by a complex system of fractures andmicro fractures. The hydreoarbon bearing zone consisk of twornsin intq@s. The upper interval is a Breccii dolomite. of Upper

-C@a:eoys P@e~ne origin and is approximakly 950 ft thick.The lower intqvsl is a dolomitk limestone of Me&rn sndLower .~eta:eous origjn zihdis2700 ft thick approximately.

The Cantarell complex was discovered ii 1979 witi the t%st wellA@ IA which. produced 340W BOPD of 22 API. The initialprodu&on w* &ven by ro@luid expansion which was short-Iived ss the reservoir pressure equal to 2375 psi at 3281 ft belowsea-level, was dose to the bubblepoint pressure of 2133 psi,Fiigu* 3. The field produc&d 1.2 MMBOPD in 1981 with 40production wells. Some of these wells produced more than 50

J@OPD each. By mid .1.994 the ye+dy production was 890 ~ L...MBOPD with 140 wells and the cumulative oil production untilmayI1993 was 46.47 MMSTB, Fi@ire 4.

,+

2 AKAL Ff6LD (CANTARELL COMPLEX) Conditions OF EXPLOITATION, ANALYSIS AND PREDICTION SPE 28714

anku

At present there exists a gas cap due to the gravity segregationmechanism present iii the reservoir. The lighter gas, whenliberated flows to the top of the reservoir. ?he reservoircondltiois are favouiable to the formation of this secondary gascap. The large reservoir thickness of 2700 ft, the highpermeability of about 3500 md aod the.kigh structural q+ief of6562 ft, all aid in the forma fioiofthc gas cap.

lltc formation of-asecondary &cap it?.cie%cs tie displacementeffltiency .The oil recovery witl gravity segregation isapprOximateIy 7Q~ r~d i.sw sen~tiv? to the.modu~on ra!e.A drop in flowing pressure due to the.increase in production rateresults in more gas liberation and iis segregation m$e top of theresexvoir.

~ a -0 t

There ae several different methods available to define andmonitor the advance of a gas-oil contact. Some are. based ondirect well observations while others are based on evaluation offluid properties to indirectly detitilne gas presence in tiereservoir.

l ~~, T*

figh gzs.oil &ios. ob&edd&ing production well-ret: U: V.indication of the movement of the gas-oil contacts. Table. 1 listsgas-oil ~atios ~huined during production well-tests, that wereused .to monitor nmvements. inthe fluid !e.v.elsin .diffemnt partsof the field. Welf-head pressure trends are shown in Figim 5 andTable. 2. The wells having well-head pressures higher than theaverage wdue and accompanying gas production problemsindicated iweas with substantial movement of tie gas-oil contact.

l we]f.*~ _.

Neutron Lcu?,%

Newmms are electrically neutral sub:atomic particles which havea mass simka to the. hydrogen atom. The CNT t.fro! bas aradioactive source which emits high energy neutrons. These highenergy neutrons collide .tith the nuclei of ,@grna:iOn._glemen~and lose energy with. each Collision. .~e klrg?st...en%Y 10ssoccurs when the neutron collides with a hydrogen atom since themasses of the two particles are similar. Neutrons which have lostenergy @er several collision:. re+h a sqble level of @ y?r~callti w.be~d emxgy , _and, arg_called !!.h~mal neutrons.?hernwd neutions are..subs.equently captured by oth~, W?ms andthe capture releases gamma radiation.

TIIC CNT tool detects thermal neutrons with two detectors atdtiferent distances t16m the source, When the hydrogen

concentration in the formation is high, most of the neutionsemitted are decelerated quickly and are captured a short distancefrom the source. When the hydrogen concentration is low, theneueom may travel ,a larger distance before being captured. Thetool uses the readings from tie two detectors tm indicate aporosity index cma linear scale.

Liquid hydrocarbons have a hydrogen index similar to water,whereas gas has a. very low index which changes with pressureand temperature. Thus the tool shows a low porosity m gaszones, thus allowing identi~cation of .fbe g--liquid COII~CL

l ~

Like the Cm tool, ihe TDTtoOl emits high em%y n&utiOnsadmeasures the number of thermal neutrons present. The detectionis done using different timeintwals which iiiow determinationof lhe rite of decay of the tbemnal neutron population. Thkdecay is exponential and is dependant on the density ofc@ureelements present

u= of z

The tool provides the following parameter..c. thermal ckcay time constant (W, micrOsec).Z capture cross section (cm, capture units)

where Z = 4550/z

The following are common VSAISfor fluids found in reservoirs.

Water: X=22 -120 c.uOil :.x= 10:22 C.uGas : X= 2-10 C.U

Use of count rates fromdWerent detectorsThe spacing of the near and f= detectors mkhizes the effect offluid in the borehole. The TOTtool provides curves TSCF andTSCN which are the far and near detector count rates. In high oilsaturation zones there is a small separation between these two .curves which are generally parallel to each other. The two curvesseparate in gas zones and allow identification of gas-fluidcbntatts. The curves ale also influenced by Iithology of theformation. ~

Use of the fNPD curveThis cur?e indicates neutron count rates at the far detector and isvw sensitive totbe presence of gas in the formation. It is lesssensitive to Iitho!ogy and porosity and can be used to confirm thepresence of gtiiri-combiiiation with other methods.

Several examples of the use of TOT logs to determine gas-oilcontacts are shown in Figure. 6. Log presentations may differdue to change of the version of softwze used.

.446

. .

SPB28714 ARMANDO GODINA AND ALFON.SO RODMG~ 3

Jiiw~Q -OiI

The movement of the gas-oil contact has been monitored byusing CNL and TDT base logs and then cornpadng these baselogs with logs run at later dates. A summary of the logs analysedto monitor-the advance of the gas-oil contact is shown in Table 3.The most recent logs were recorded. in May, 94 and the resultsare included in Table 3. ... .Figure 7 shows tie tiiwiment of the gas-oil contact wiffi $meusing TDT logs. During the first few yeiwsof field exploitation,the gas-oil contact advanced at 197 ftfyr approximately (Figure10) and was matched using a hyperbolic curve. The presentadvance ii 98 ftlyr aWroximitely mid tbe.d+rease in the rate ofadvance is due to the larger ama available for gas expansion withtime. The matched data may be used to predict that the gas-oilcontact will be located at 6339 VftBRT by the year 2000.20production wells were deepened in order to move away frOm.thegas-oil contact. Wells Cantarell71, 28,55 and 69 were deepenedafter they started to flow gas. The remaining wells were deependin order to prolong their productive life, Some wills witi highgas-oil ratios were plugged without deepening because ofoperational factors Elating to the production cdinplexes now inuse. Among tiese we have Cant&ell- 1A, 3, 1I, 22, 74, 78, 94and 1084.

Table 4 highlights wells @at were deepened to avoid the gs-s-oilcontact and the cumulative production of oil since their workoveroperations. The cumulative production until Jul, 93 attributed iothe wells that were deepened is 4629 MMSl?3,

Pred iction of the movement of the Gas-Clil cow

The data obtained about the gas-oil contacr using TOT logsduring the productive history of the field, wti nm.tched sig ahyperbolic curve in Pig=re 8. The equatlm bflthe matched curiewax

H = 3892.48/ [1+0.01035 ~lnS..,.,..., ...... ...........(l)

where,H the depth of the gas-oil contact (VftBRT)T time i~rnbnths since May, 1981.

Extrapolating this curve until Dee, 1995 indicates that the gas-oilcontact will be located at 595.g VftBRT, a movement of 446VftBRT.since May3 1992. II - - .-

A match of the gas-oil contact movemem versus the cumulativeproduction of oil is shown in Fi@e 9. The matched curve waswell defined ad will help to monitor the advame of tie gas-oilcontact using tie pam.meter Np. It will not be mcessaty to maleadditional periodlcTDT logs in order to monitor the advance ofthe gas-oil contact. The hyperbolic curve which relates tievalueof Np with the ga.-oil contact is:.

H =-3796.36 [1 + 7.115X 104 * Np] 1C5W.............(2)

where,H depth of the gas-oil contact fJVtBRT) =Np Cumulative Production of oil (MMBbls)

JVorkov $rP1mt: .

The preceding predictions provide & estimate of the movementof the gas-oil contact until 1996, it which time it will probablybe. necessary to change the perforated interval. The resultsobtained are listed in Table. 5.

Gas LiFt S-

Based on the declining well-bead pressuk.s and the high back.pressures present in operational surface iintallations in the earlystage of production, it was concluded that it would be necessaryto impkrmnt an artificial pmdction system i order to extendthe productive life oftbe fiefd. The system seIected was the useof gas-lift with ah original design of ijectim rate if 0.5MMSCFD/welI starting in 1986.. At preient -there is a 20 g%pipeline ring; Figure 10 which supplies 128 wells with aninjedion pressure of 995. pi and a rate of 0;3.-05MMSCFD/weO,

The historical pressure and cumulative production were matchedusing a volumetic simulator i order to study difermt recoveryschemes and future pressures trends. The results obtained inFigure 11 indicate a good match with historical pmdwtio rates.The results indicate the ability to maintain a production of 900 ,- ...MBOPD until 1996 and a decline in production rat% followingthat year.

These results contirm the med to implement enhanced oilrecovery methods to increase final oil recovery.

Conclusions

L The Akd Field-from C&tareO Complex ha.i favorableconditions to. the .pvity segreg~ion mechanism, Thisconditions are large reservoir tMckness, high permeabilityand high structural relief which @d in the fongation of thegas cap presetitkt the reservoir.

2,, Based on hyperbolic curve. match of the movement of thegas-oil contact with time using TDT logs, during the fityears of field exploitation, tbe contact advanced was 197ft/y~ approximately, at tie current time the @vanm is 98ftlyear. The rate of advance is due to; ~e larger avdlablearea for the gas expansion wiib time.

447

,,

4 AKAL FE3LD (CANTARELL COMPLEX) CONDfllONS OF EXPLOTATfON, ANALYSIS AND PREDICTION SPE 28714

3. One correlation of the gas-oil contact movement versuscumulative production of oil was done. The match of thiscurve was well defined and helps to- follow monitoring theadvance of the contact using the parameter Np and will notbe necessary to make TOT logs in frequently way.

4. Extrapolating both curves until 1996.we know at which timeany well probably will be invaded and be .PW?SSWYtopredict his workcmer for change the perforated interval.

Nomenclature

CNLDftRRTDftDTGORHINFOMMBblsNPNPH1%PmRHOBTTDTTSCFTSCNVftBRTVftx

T

..Compensate Neutron Lag.+Developed feet below rotary table: Developed feet

= ~z-Wave sonic velocity, @%lft)=..

.-

( ,I /1 -Q.

Fig. 1.- Akal field location

,,..-a

.i_4 3.r

,..

Fig. 2Wucture map of Akal FieId,top Br?.cciaFormadon :449

SPE28714

0 lW Z,cia 3,CW 4.CQ3 !-W w,

J..rls$m2Mms+m2m. w. . . . . . . ---- --

1,800

Fig, 3,- Behavior static pressure versus depth ,,

Cumulative PRODUCTION, OIL RATEVERSUS TIME

6 0 A-cm-alWats(w -)

Fig, 5.- Well-head pressure behavior wsus tl~e

GOR VERSUS TIME

I

0J,,m JUw,m ,!.3,, ..Am .w,a, ,.?4 JUw m.. ,.., Mm ,,.!4 Ju,no ,,)+9, ,,., ,..,, mm ,

TIME (YEAR)

Npc!o

,,

Fig. 4.- ~kal Field, cumulative production, oil rate and GOR versus time,,

,11,

! ,,,,,1,,, {:$, !I

.,-

I .- ---! I I

I I 1

,H, m, ,s.

Fig. 6.- TDT logs eXaMpleS.461

m.. __. . . w .!-0 I

.--, .

.& :.L.,,.

. . . . . . . ..... . ..- .-

o00.0

0-

00..

00 :..=

0 ...... .....- .

452

. . .

.. .

;TP=,~..= SPE28714

GAS LI~ FACILITIES

Fig. 10.- Configuration 8f gas lift facilities

,,, ,.!, ,. ..! .,. ,., $ ,,1 1 I

1992 1994 1938 1998 2000 2002 2064 2006 2008 2010

Time

Real Prediction+ ...*..

Fig. 1.- Akal field, production profile with volumetric model

453

- . .-!. -, .

TABLE 1 WELLSW,T!+ H,@l GOR -

W@J mm mm ., m mm . .

m Ww, IlM4Sc80, . .

-,,4 =JW. 1 0 27.!24 .- ,%

w.,. !WAm . . ,,,,,, ,,n,

w. m ,Wvw , ,2s ,o,m4 m, ,*

W.ff , MU , ,,m ,,,72 ,* ,,=,

UW. ,W 21WU4. , , ,,$,, a,= ~, .

Cim. w *- , am ,?.! ,C4 .

W.78 2WW86 m ,,6X ,,,,2 ,*, .

W.!4 WWMS7 ,,,, .- ,.,, . .

-,=

WW87 , m !,0,$ ,2.3ss 94, ,,,

m.., 2W,87 2 ,,,2+ ,,m . .

m.,, *,U.M ,,. W, ,.,, mm ,!6

w.!> M,?/#13 ,,, ,24 ,U4, ,,,s ,,0

.Mm-me. m

,.

SPE28714

~~sw 2 MLL.HEA6 PREs.suP.E 6E.HAWOR

Illw.

/,0,,0,.wm vmw m,m vmm ffiwm>c-.. . . . . .. . .

u I 55 I SEE I ,, ,-! I 7A ., !.., ,.., ,., , ,,.1 ,1.1 , ,.$. L-H 63

-- . .. . . . . . . . . . . . . . . . . 1

F I 14F ?4F I 14

D 37 1 JUU93 IN 108?

1

m,,-,. ,

F t4[ 25E. 93 , AU(! 25 t !#t C,., ,77s 7751 1 598, 57,, 1 ,.. . . .

E. 93 MAYn4I I 8104 6939 I w 5719I mrm

454

.,-. .

WELL PRCCUCER INTEWAL CEFW WORKCNER DATE1(

NP, N~ [JUU93) A NP@EFORE $nBv . PRESENT MMBLS) fMMBL31 (MMBLS)

6A 55e4. 5e56 6?4,.7382 sEP/33 31-309 S2.385 52.076

7A 5020- =43S ml .7300 JUN188 31.544 53.616 27,072

8 5872. S489 7s85 .77$3 AG0134 31.372 74.292 42,420

14 4557. 474t 6868.8995 AUG163 35.332 62.144 26,812

17 5157.54X m -6795 0cT188 30.094 45.400 45.309

19 6365.6398 7877-7954 JUU88 60.299 73.609 13..310

25 S4C0, S571 725i.73z3 JANf87 43.075 626!9 19.604

20 5823. 5C@8 WC. 742i FEB/34 25.4T9 62,324 36,905 .. .

28 6K35- 6257 6509. 66C4 JUN/90 50.921 60.54i 9.62a

31 %27 -5676 6650.6722 JUN186 37.179 S5,892 28.703

35 4M4 -5203 67ffi.6857 AU(5,82 13.0Q5 62,689 49,6e4

39 8237-6434 65,? .8621 0EC!90 53.074 59.901 6.827

51 4259. 440% 702$.7419 JUN135 17.476 30.535 13.109

53 5,94-5751 6539 .6s31 SEP185 38.8T2 65.983 27.111

55 5377 :s73s ,509.6578 SEP189 48.936 58,058 9.120

59 5630. 58s6 6808.??73 FEB190 51.443 60.543 9.095

71 3570.3658 S305 5SS JU!J81 10-562 27.919. 77.357

71 5305. S%4 %46 -5755 0CT139 27.919 33.163 5244

73A 535t. s548 6539 .C611 AUG186 42,203 34.052 27.769

94A 4+99.4403 5248-5495 SEP130 8.956 52U24 a 43.068

34 %7, .,,88 64,0 ..$5!6 NOV/90 53.056 59,714 6.055

TOTAL 462.9~3

ANo = PWUCTlON lNW.EASE-WZTC REDW-LW (ND, NP, }No, = CUMULWVE PROOU~~ AT WRf@J~ ~No, - TOW CU1.WLKWE w.OCK!rXON .7 J&W -. .. XT AG,&S0 ., AT .0485

TABLE 5 wELL INVASION FORECAST_

PRODUCER lNTERV41WELL PLATFORM

PROBASLE ~@jp~~,o~ LASTrC&G M~ORINVAS!ON DATE WORKOVER

DRBRT vfiBRT

37 AKAL-D 6670.6969 5790- 5@66OPENAPRlU95 HOLE 4 3/2 NO

57-A AKAL-D 5787- S83D 5187-5330 9FRIU9+ yo~ 7 YES

95.. PJCAL-E 8300-.8399 580.0 .5804 MAW95 cH.&D 4 (/2 NO

46 AKAL-G 676.8..6978 %03 6Q63- MARCH!96. ;;~ 9 5/8 YES

24 AW-F 6926-7090 5892-6027OPEN

APRIL% HOLE 7 YES

- HO*,ZONTAL WELL

455