Paper Saturasi

8/9/2019 Paper Saturasi

1/10

.,

SPESPE 20095

Saturation Evaluationof Secondary Recovered ReservoirsMN. Hashem, StanfordU.

SPE Member

Cepyfeht lSW, Soclatyof PetmfeumEnginssraho.

Thispaperwaspreparaofw prwantdon attheSOthOelifomlaRagloMlMwtlng M InVeIIfUfa~MwIk W 4+ 1~.

mh~Wtid W~tiby MW-Wmmwfd~ -tilti*-ti hM~*M@@W X8). MtiWdti~.u-td, hmMW~WtMWof Ptim EwlHtimq@~ bytheawtt@a).lha msfertd,eaWtented, downOtMwaaNYrSW0fa =timo&ietyof PstrobumEnglnwrs,Ifsoffkets,ormembefa.PaPWSpreesntsd t WE mestlnrpmsaubjecttornMWon ISI&WfWEditdelOOmmttfeesoffhe9GcIwY

.Mmlsdcmtoc@[email protected] maynotbawpIsdllWJsba&ectahaddconta ncOn@wW$~ofwhereandbywhomthepaperISpreaentad.wrfte PwbfIwtbnsMSIWJW,SPE,P.O.BOX, R~, TX 7ZW?-3W. Telsx,7W9SS-L

ASSTRACT over the zone and from one well to another for thesame

Consider the case of a eand atone reservoir thatzone, depending .n tha posit ionof the well

has been under a water or steam flooding program,from the flood profile ) .

that was not efficient. A lot of effort is cur- This fact was real izedby the indus tryand ratherrently being done to evaluateand recover the oilthat was left in the ground, As the flood flutd

expensivemethods are followed,such as extensive

has now been introducedto the Reservoir element,coring,NuclearMagnetism tests, and EPT logs, etc.

i t becomes very difficult to find the value of thejust to detarmt~e the oil saturation over thoseunswept zones.

water saturation as the salinity of the floodwater is different frorsthe original formationwater, and involves a lot of coring and other rhispaper.offersa solution to this problem thatexpensive operations to come up with the value of could save substantial expenses to answer thatSw; water saturation. particular queetion. The results of this studyThe technique suggested in this paper finds the were compared to other saturationvalues obtainedvalue of the maturation using logs, both old and by core analysis, E PT and GST logs. The resultsnew, that are available for that field ,theoldbeing the original r esistivity l ogs and the new

were agreeable,and will be discussed later.

being the logs of the new well drilled and record- The real data tested is a case in the Wilmingtoned after the flood. field,CA.This techniqueagrees very well wi th the satura-

~is fiald is a typical c ase of a longproducer that underwent waterflooding and the

tion obtained by other methods including otherlogs

chances of bypassed oil are very much there.such as the EPT log, and the core analysis Fig.(1) shows what the problem would look like on

results ,within a tolerance of ~ 7%. a resistivity log,where a new water zone hasformed within or above the oil zone. That watim

INTRODUCTION zone has the characteristicthat its SP curve

In many fields that use water or steam flooding,full deflection d oes not reach the SSP value of

the problem of fingering and bypassing some of thethe clean thick adjacent w et zone that was notmixed with the flood water. Yet, the resistivity

oil zones frequentlyhappen. As a rasult, programs log shows low resistanceindicatingwater in the

are made to recover the oil that ia left behind in formation.fhisndicatesthat those two waters arathese secondary recoveredreservoir, The questionbecomes; Howmuch oi l is lef t behind ? .

different;the newer being fraaher.

The problam now is that the pay zone is partly The solutionsuggestedin this paper will uti lizeflooded, that leaves the old oil zone split by a the conventional Archies (Pickett) crossplot ,new water zone or any other shape that might formdue to tha new presence o f the flood water. The

with some importantmodificationsto suit the newsituation. From there we will arrive at a new

new water zone, however, does not have the same defined 100Q water line ( Ro-Line )which containssalinity as the flood watar or the original format-ion water, but rather somte sa linity inbatweeq,

the new water regardlessof ites mixture, and that

that makes the saturationevaluationfrom resiswill be our base line for evaluating t he satura-

tivity curvas a cotspltcatedroblem. (Rwwill varytions of the adjacent oil zones, ( in this casecould be above or below it, as shown in the

...----.-....e..........-.--References and +llustrationnat end of paper.

figuresattached of walls lB&2B).

-.am


2/10

2 S ATU RATI ON E VALU ATI ON OF S ~ ~ ARy R~ ~ ~ ~ .RE D R~ = Rvo~ s SPE 2(X)95-. .-. .. - -- .-. -- --.- .Statementof TheorY and Definitions where there is compaction ,or steam flooda that ~

Our fundamentalequation %s Arcnies eq,:-could desolve some of the grains of the formation,the value of m w ill change and a solution to

Swn - Ro/Rt-~w/Rt . . . . . . ... 1that is also proposed in this study.Shel l proposed for m an equat ionwhich dependa

m on poros ity :Where F- Formation Factor = a/ l . . . . (2) m- 1.87 + 0.019/fJ . . . .(8)

aleo F Ro/RW . . . (3) B/ a : FormationFactor Constant :-

substituting(2) in (3) we getm

1- Surface conductanceand ionic mobflity in wateti

Ro-aRw/fl . . . . . ...(4)films: * Cations Exchange Capacity (CEC).

that leads to* @sntity of water absorbed to clay

particles.

logRo - log (sRw) - m log(~) . . . . . (5)2- Salinityof the formationwater.3- Wettabtlityrelationsbetween particular solid

lhis is a straight l ine on a leg log plot ofsurfaces and the Hydrocarbon.

Resistivity (Ro) vs Porosity , with a slope (-m)4- Presence and distributionof electrical

and intersects $-1 at (eRw).conductive solid minerals.

Ro points are the lowast NE values of the RtHere we can see that a could possiblychange and

points in the original formationwater setup.for tha t reason this paper works wi th the value ofSRw. If an accuratevalue of Rw-new could be

In the case whera there is no sufficientvariationdetermined, then the value of a couldbe calcu-lated. Values of a vary bemieen [0.6 - 2.0]

of porosi ty to const ruct such a plot, then eq. (5)mostly considered-1.0could be rewritten as:

LogRo- -mLog (RHO -RHO )+Log(aRw) . .(6)C/ n: Saturation exponent

ma log 1- Volume percentageof oil.or

Log Ro = -mLog (Dt - Dt )+1.og(aRw) . . .(7)2- Distributionof oil.

log ma3- nettability to 011,4- Degree of interconnectedbodies through pores.

Conventionally this wouldbe a way to determine5- Interracialtensionbetween brine and oil.

the values of the Cementation Factor (m),6- Degree of electricalisolationdue to wetting

and by Oi~.knowingRw, then the constant (a) couldbe deter-mined. nvalues normal ly range between 1.2 - 2.2 taken

This Ro-line would represents100% Sw line, satu-mostly as 2, however this method will allow forvarying the value of n .

rat ion of any point could be calculateds imply by A widely used formula isreading its resistivityRt value, and project i t 2.15vertically (constant~) to the Ro line to get Ro, F-O.62/$fthen the water saturation of this point is the 2value givan by equation (1). or F .81/~

The limitationsof such techniqueare:-called Humble equation for sands.

Other aquations used;2

1- For use in clean reservoirs rock, as shaly F- l/@ for compacted f ormations androcks wil l cause sw to be predicted too high. chalky rocks,

2- Format ionmust have the same minera logy, for The presence of oil and gas produces n valueacomplex ltthology m will vary from one type ofrock and porosity to another.

which vary with saturationand nettability. Inwater wet systems containingwater and oil , when

Figure (2) shows the conventionalArchies cross-oil saturation f s below critical, o il exists inInsular globules.

plot.Theapherity of the globules

Factors Effecting the Values m,a,nwill depend on its size with respect to the size

of the pore, and the inter racial tens ion betwaenA/ m:Cementation,Tortuousity,or Shape Factor:- the reservoirwater and the crude oil . Aa spherity

decreases, the saturat ionexponent n wi ll in-1 . pore Geo~try: ~ surfacearea, vohlme Of ~raill- crease. n increaseefurthetwhen oil saturation

angularity - spherity. is above critical nd insular g lobules of oil ce~nt.ation- compaction. become intcrconnactedthroughouttha porous meclia.* ~ifomity of mtneral mixture. As oil saturation increases,the electrical fnter-

2- Anisotropy ference producedby the oil increases, that causes

3- Degrae of electric isolationby cemantat$on. n to ksep increasinguntil the water volume has4- Occurrence of an open fracture. been reduced to irreduciblefiha.

m valuee will range from 1.3 for fracturedrocks Looking t the factors ffecting m ad m wto 3. nom the factors bove we can see that it find that we could asstwa that m would stay thewould be reasonable assumption for thie paper to same, nd a would clmWe ali@tlY~

conai&r ths value of m to be constant. Xn casee*-


3/10

.

SP E 2009s M OH AM E D N . H AW I E M 3

tioweverto account for the disturbance in the clay is the porosity corrected for wet clay.Mstr ibut ion or content of the porous media that If the new point falls on the water line, thiscould influence these parameters, this study will is the EffectivePorositydaal wfth the effective p orosity ($e), and dealwith (sRw) as a term, and leave the value of (n) 8* If the new point crosses the water &_ne, someto the different u sers to apply their imperical Hydrocarboncorrec tion fs then needed . Forvalues. that determine tho Hydrocarboneffect direct-

ion and that is ganerally in the NE direction,TECHNICALAPPROACH so its corracti.onis in the opposite direction

to bring our new point dotinto the water l ine.This paper s approachwill differ from the origi- That is the Effective Porosity corrected fornal Pickett work in the followtngways:- Hydrocarbonand shale effect.

I . Model assumed is the Dual Water Model, 9* If the new point stops before the water line ,~ (3-3a-4) shows the distributionof the then heavymineral correction is needed tofree and bound water, and it couldbe summed bring it up to the water line and that willup in the following form:- give you the effective porosity, corrected for

shale and heavy mineral effect.$lt= ~e +$ne

10* To find the total porosity, one must first11.Porosityused is the Effective porosity (Oe) determine the clay density,thatwould inters-

which is the HydrodynamicallyEffective Poros- ect the extension of the lime connectingthaity. water point(l,l),withthe wet clay point (WCP)

at the Dry Clav Point. Any line drawn paralle lNote in Fig-3A, that the irreduciblewater satura- to the line connectingthe matrix point to thet ion is par t of the free water, while the bound dry clay point, f~om a given originalpoint,water is part of the bound water saturation. will intersectthe water l ine at the

Total Porosityof that point.Fig-4 shows the increaseof shaliness,ina model.

Figure (6) shows actual log values plotted beforecorrection, and figure (7) the same points aftercorrection,on the water line, giving the EFFEC

To determina Pe there are numerous methods, one TIVE POROSITYvalues used in this study.of tha ways could be obtained through computerprograms in the logging unit, provided a dual III. Rt: True FormationResistivitywater modal is used for clay correction.A graphi-cal method will be introducednext. This term is obtained from the DUS1A graphical way to get $e ie :- Water Model, where :-

1* Plot (~ ) or Bulk Density Vs (p ), Rt - f(~e,fie), but @ -$e +flneD N then

and construct the graph shown In Fig.(5),. Rt - f(~t) , and

include in the plot points .:romclean wet Total Water Saturation; Swt- f (Rt,@).zonesa as well as some shaly zo..ws. As we are seeking tha effectiveSw, for bette r

Hydrocarbon saturationdetermination,2* From the origin ,0 draw a ta~gent line to then

to the cluste r of poin ts to touch them at thai r Swe-f(Rt,~e) . . . . . . . . ..(9)lowest point.Point(O,O)is the [matrixpoint].That line is the [Shalinessline]. The material Balance for hydrocarbon volume in

water wet rock:-3* Froa the point(l,l) [Waterpoint] draw two

l ines; one to point (0 ,0) -that will be the ( l-Swt)jZt- (1-Swe)j%e. . . . . . . . (10)effective porosity or clean matrix lina. thenThe second line is a tangent to the cluster of Swe - l-[@(l-Swt)/~e] . . . . . . (11)pofnts to touch them at the most southwest wherepoin t. That is the [Wetness Line]. Swe ~ Swt

A* The intersectionbetween both tangents,thewetnass and the shaliness,will give the

JWET CLAY POINTI.PROCEDIJRBOF SW DETBRHINATION

5* Scale the Shaliness line linearly from ZeroIf old logs, of a near by well that were recordedbefore the flooding took place, are available,

at the (0,0) point, to 100* at the wet clay - then construct the [Resistivity- Porosity] plotpoint. disczsviearlier. If both density and neutron

6* calculate the shale volume Q by any method,logs wede recorded, then follow the proceduredescribed above to coma up with the effective

preferably by the neutron-densitymethod, andapply it to the shale-l inescale, and

porosity, nd evaluate the value of m and (sRw)

measure the equivalentlength on that scale.old. Then follow the following steps from step l.Wa will discuss both situations,but first;

7* maw fr~ eve~ Qoint a parallel ltne to theshale line , and mark the measured length ofstep 6, start ingfrom the point Itself. that

H


4/10

.

4 SATURATIO N 13VALUAIfONOF SIKCXQ13ARY R~VRl?l?D RI? W?RVOIRS S P E 2 9s.. --- .... . -- . - -.-

If the old 10KS are not available,using new re- The S@xration determinedby thi method greedcorded logs. the most with the cores with a difference of ~ h

and by -10% to GST Saturation, and =6* to the UPTSaturations. The differencewith the SPT and the

1* Pick a wet zone, on the new log, that would GST Saturations is influenced by the fact thatsti ll show the old formationwater, in the example they investigate in the inva&d zone, and as theshown in Fig.(l) that was the upper water zone, as oil in this case is quit heavy the dffferance isthe most llkely explanation shows that the upper not much. Results were also compared with comput-portion of the otl zone wae sweptby the flood. arized packages of ~gging Service c~aniee and

it agreed with around the seas tolerance.CONCLUSIONS

Cautisn should be noted , in excluding the zonethat the higher resietive wet zone ie not due to * The saturation values can be &termined withless porosity. Read several points in both old reasonable accuracy from the Resistivi.ty Veand new wet zones, as wall as the oil zone to be EffectivePorosity Croesplot.That could raault inevalua ted,p lot them on the Log-Log plot of Rt vs huge savinge due to less cortng needed.~e obtainedby the method explainedbafore.

* Old records of the f ield are very deeirable to2* Pace a line through the lowest NW old water determine the original formationparameter morepoints. Find the slope (ml); and the value of(al*Rwl)at the intersectionwith ~e-1,

accurately , however, if not vailable tha resultscould be still cbtained , as euggasted by thispaper, by searching for a zone that was not flocd-

Slope m - [Lcg(sRw) - Lcg(Ro)] / Log 06 ed and obtaining the originalwater parameters (m).,. (12) and (sRw).

The value of Rol is the value read on the Ro-lineof the vertical projectionof the point (Rtl,$el). * The values of (m) could be accurately deter-

mined, if the effective porosity ie used. That3* The new lowest N Ewet points should fit a will correct for the shale effect, also will leadparallel line to the old Ro-line. This parallel to Swe.line is displacad away due tls difference of6al inity between old and new waters. I f tha mate- * Applicationof such a method is scheduledto berlal balance of the formation was not tested in different lithologies, ndwith differ-maintained;(i.6. injactisn r ate is not equal to ent types of flood recoveries, co test for thethe productionrate) and subsidenceoccurred, the saturations.value of (m) could changa for the new water zone.In that case find the mean ovar the new water zone NO14SNCIATUREp o in t s a n dp a e s a parallel l ine through it , thatwill ba the new Ro-line, for t ha t c a se La t er Bou nd Wa t er : Layer of water h e r i n g to thecompare this l ine and the value of (m) to another shales, describedby Rwb,Swbnwell were the same subsidence problem did not Free Water : All water not bound, describedbyhappen. Rwf - Resistivityof free watar

includtng the irreduciblewater5* That new Ro-line becomes the basis for thenew ttaturationevaluation.Its intersection with Total Porosity :*Fractionof unit volume occupied~e-1, gives (a2Rw2) by fluMs* - ~t

Effective Porosity :Frac tion of unit volume6* Simply for any oil zone point of a value containing the free water(Rti, jlei),rop verticallyto thenew Ro line and and Hydrocarbonsa- ~,read Roi,then the EffectiveWater Saturationis :: Rt - True formationRe6istivity (oh@.

Rw -Resist ivity of FormationWater (ohm).Swen - Roi/Rtl Rwf. Resistivlty of F r ee FormationWater.

Rwb - Reeistivityof Sound Water.7* The value of tha maturation exponent (n)could be elways aesumed the old value as its Swt - Total Water Saturation.change, if ny, will change the maturation values Fractionof total porosity occupiedby

obtained very slightly .water - both bound and free

RESULTS COMPARISON Swe - EffectiveWater Saturation.aFraction of I occupied by water-.

Figures 7A and 8 show ct@ &ta points frOa 2S* . go@ Water Saturation.

di fferent wel16 that showed two different poei-Vrac t ion of ~t occupied by bound wat*rm.

tio-l~for the new water line, one was less resls-t iv~ (fig.-k), and the other more re8istive. n

- Saturation Exponent in Ar c h ie s equstton.

In both cases the Swe wa calculated t o the newm - Ce?aentatfon,Shapa, or Tortuousity Factor.

lines os shown on the ftgures . RNoma=llatrix density (gm/ce).

Reeults were compared to differant sources ofmeasurement, uch e core Saturationvalusa, EPTand GST logs Saturations.

-


5/10

- ..VV. LV8US lruvu lx. Ku-Aim SsaLra

RHOlog- Log density value (bulk density) - gin/cc. 5- Fricke,H. :llm Electric Conductivityand Cap-acity of Disperse Systems

Dt -Matrix transit time (u/ft). Physics,Volume 1. August 1931a

Dt = Log intervaltransit t ime, 6- Norris ,R.L.and Biggs ,W. Using Log Derivedlog Values of Water Saturationand Porosity,

Trana., SPWLA, 1967REFERENCES

7- Pirson,S. :FactorsWhich Effect True Formation1- Archie,G.E.: The ElectricalResistivityLcg Resistivity. Oil & Gas Journal Nov.-1947

es an Aid in DeterminingSome ReservoirCharacteristics.AIMME Ott.1941. 8- Porter,C. and Carothers,J.:FormationFactor -

PorosityRelation Derived from Well Log Data ,2- Ransom,R. :Tha Bulk Volume Water Concept of Trane. SPWLh 1970

ResistivityWell Log Interpretation.Lag Analyst - Jan.197& 9- Wexman,M. and Smits,L.:ElectricalConductivi-

t iee in Oil Bearing Shaly Sands. SPEJ June 683- Serra,O. :Fundamentals@fWell Log

InterpretationPart Two, ELSEVIER 10- Wyllie,M. and Gregory,A, : FormationFactorsBook Ser ies - 1989 of UnconeolidstedPorous Media: Influence of

Particle Shape and Effect of Cementation.4- Atkinson and Smith :The Sigrdficanceof Parc- Paper 223-G, AIMS, Houston,TexasOctober 19S2

icle Shape in Formation ResistivityFactor -Porosity Relationship. JPT 1961 11- Serra,O. SedimentaryEnvironmentsFrom Wire-

line Logs Schlumberger 1989

m


6/10

SPE 20095

/

+-n

p 1 1 I I I

1 I I I Jeao

EEkuI 1 I I I

tsoot

%1 Iit

I 4 i l t

1S&l =EbtlmHFw H-el=t

I 1 I 1 I I I

I

l+ , I I 1f:fi

1 m I Iesoo

2700

l++

I I 1 1

ll~ T.EF


7/10

Simple ARCHIES Cross PlotLog Ro Log (aRw) - m Log

100

10

1

0 w-4--- I I I I I I

I I I

. SPE 20095

0.1 I II I I 1 1 , 1

0.1 1Porosity

FIG 2

DUAL WATER MODELFREE & BOUND WATER

rs Sw I SwHC F B

ar

FIGURE -3

EFFECTIVE & TOTAL POROSITYSHALY SANDS

b TOTAL

EVOLUTION OF TOTAL POROSITYWITH SHALINESS

FIG. 4

m


8/10

1.0

Buk

gin/ccD

NEUTRON - DENSITY CROSSPLOTEFFECTIVE POROSITY DETERMINATION

Water poin

\

gas correction ;O z

N.

2

1,1)

\o 0. 1 0. 2 3 4

d

6 6 7 8 9 1

NEUTR POROSITYeavy$~i},

/

\/DllYCLAY R?iNT

qg. s4nphkdrnbthodc+f 6@urA%th.

YHX1=KHUB (&-c3> Y} Ull=llmlt0.0 .16667 .33333 .50000 .66667 . e3333 1.0

1.0

1.4

10s

EGz .

2.2:

.

2.6

~,:y,./

3*O ,-----------

~lE JTRON pOFiOSlry~ - -- xrUtl-l DEtlW1=I PIII (Ssfw)

PLOT OVER DCPT,HS 2666 TO t?154 fTPtm IS wtc..m=T:v= puRusITVS

Fb.-- d dbUtdm*b-h~* ~

no

00


9/10

rlii~ a OS-MY-ES 10:03

1.0

1.4

1.s:

6zIllo

e.25

ii

2.6 J

3.0

YAX1=RHOB (WC3> YrUH=I0.0 .16667 3

. .

PLOTPHIE

:?4133 .s0000 .66

r

67 . e3 33

[email protected]@**.

ARCHIES CROSSPLOTWELL lB

sPE 2009s

.0000

KFUN=lDEN

100

Rt10

1

0.10.1

EFFECTIVE POROSITY

Ro LINE1 + HC VALUES * new Water

R3.7a-mmm@90fRo (Ilmv)do(om

1


10/10

wELL 2BOLD/NEW WATER

I , 1I 1 1t \\ f

1&

III

I I I m= i I Im .2.0 I I I I I

I0.11 I I IW

0.1EFFECTIVE

1

POROSTY

ORIGINAL + NEW WATER

m. M*>RO*.

I

an

Documents

Paper Saturasi