A Method for Determining Permeability From Well Log

7/28/2019 A Method for Determining Permeability From Well Log

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.& ME!HOD 1I'OR DE'l'ElOOlfINO FORMATION PERMEABILITY FROM WELL LOO DATA

Jar1 P. Johnson levan.. 011 CompanyOdes., TexasTbe OpiniODs ezpressed in this paper are those o the author and are notnecs_rtl.7 the opinions 01 the Soc1ety ol Prolessional Well Log Analysts or 1taIl8IIberl.

Pub1icat10n Rights Reservad!b1 .-per 18 to be presented at the First Annua1Meeting 01 the Society 01Profe.iS.Ona1 VeU Log Analysta, Hay 16-17, 1960, in Tulsa, Oklahoma, and ie COD-eidered. the property 01' the Soclety. Permission to pub11sh ls hereby restrictedto &t'l abetraot of no more than .300 words, with no illustrations, unleas the :aper

18 apeciticall7 releaaed to the Prese by the Secretar or the Editor ol the Soc-1et7 ot Ptotaa:f.onal Vell Log Analystso


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A METHOD FOR DETERMINING FORMATION PERMEABn.m FROM'WELL LOO DATAJarl P. Johnson Kewanee 011 CompanyOdessa, Texas

AJf)TRACTData trom 10gs whicb are cCIMlOnly employed in salt mud 878tems ~ be usto determine lormation permeabilit,.. An empirica1 correlat1on ot apparent resiual 011 aaturat10ns computed trom we11 log data and permeab111t1es trom -.,bole coanal1'ees has been useful 1n evaluating San Amres tormatiOl1s 1n West TeD;l.

INTRODUCTIOHA simple method for detemining formation penaeabil1t7 f'ram weU log da1s ot cOnsiderable assistance in evaluating the producing potential 01 a ve11in aking reaervoir &tui1es where In core data are ava1lable. In the ~ ~ U o w 1diSCU8110D a pemeabilit1' interpretation tecbnique i l described which use. al 1data aouree logs which are cOllllllon1,. employed in 8&lt mud B18tems. 'lbey. are thlocuaed microdevices (Kicrolaterolog or FoRa) ,an independent poros1 1' , _eur1Ddartce (Sonic or Neutron), and a device lor measuring Rt (taterolog r Guard).

BASIC CONCEPl'SWhen the Microlaterolog was f i rs t introduced, 1t vas eJq>la:1ned that i t v,a dev1ce tor .asur ing the resistivit, . 01 the fiushed zone around tbevell bo(R.xo) am that the lollowing relationship between Rm, Rmt, poroeit". and residuoU eaturat10n in the flU8hed zona (ROO) exists:

2.11 0.62Rmt V::.(,) , Rxo (2 )(1 - ROS)2 (1- ROWhere F = 0.62 Where F :1 .-L- a.lls

'!'ha. equationl are based on the familiar Arcbiete Formula,!

s ~ FR ..Rt,! L

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!he1r appl1cation aaaUl\es that the microdevice la l118aaur.ingRxo an d tba11 the eormate water has been displaced by JIllD 11ltrate. In salt _ud qatewhere the reaist ivi ty 01 the mud fil trate is s1m1l.ar to the .,..a1st1vity 01 tt.PJ.'Ut1bn water, the second aSSllllpt10n 1a relativel,. UDiJIlportU'lt. 'plot~ u a t i O D (2) vith value8 of ReS fran O to 90 per cent ia ahovn aa Fig1U'e l .

en.0a::Oa.

Fig. 1 - R:m/l\at - Poros i y CorrelationSinee no direct method was given for determining ROO, i t 1a neceskrrmake a judicious estimate of thls value in order to cOIIPute poroe1t,. frCa dobtained. fran the aicrodevices.I t is olten ditficult to estimate the residual 011 saturation in the hig17 atratit1ed carbonate rocks of West '!'exas with suf'f1c1ent accuracy to allII

UH al tbC!lse toola lar poroait,. evaluation. Net only does the ~ vart coruti4abl1 t h r o ~ h the producing zonea but i ta ind1cated value 1 . JIluch highe1" m Uperaeab111t7 Iones than the actual ROS 1a generall,. considerad te be.U an accurate parasit,. value can be obtained trom the Sonic 01.' Neut10gs and. Rm 18 available from one of the microdevices , a value tor ~ canccaputed frOll ecuation (1) or equation (2) depend.1ng upon tba tonaation t avhich 1s appl1cable. t J n f ' o r t ~ a t e l , . , aecurate va1uea of por081t,. me! . . ara nalva,.a obtainable in stratified rocks becauH al variationa 1n the petropqa1eharaC'teristics of the roeks as affected by variations in pore geometZ7 and


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limitations of logging devices in detecting these cand1tions. The complexitr bthe problem, of computing an actual value for ROO has prompted the use of a.n a ~pareht RCS factor for the purpose of this d1sCU8Sion. The apparent!lCS lactb-7 1J.80 be considerad as a correction factor for equating Rxo/Bmt to r, tbe fol_t ibn factor. Tbis factor 1s to be obtained traro Figure 1.

PERMEABILITY DETERMINATION ,In an o il reservoir, the degree of n U 5 ~ ot the Rm sone by the .ud l i1trat and therefore the residual oil saturation in that zone 1s largelT'dependefuJ?On tbe permeability of the reservoir rock. I t is expected that as the pemebUlt.,. decre&ses tbe amount of residual oil remaining in the Rm zone ,in,crea Th1I,trend cc:btinues in a water wet reservoir mtU the p8l'1leability va1:aes beco$. . . 1, then the residual oil saturat10ns will be 8111&11 because ot th8; eltect .caPillirit,. . However, the apparent ROO tactor as determined lran J'i j lre 1 .continue to mcrease. This phenomenon usually occure in resistiva au1tiple pooeit t type rocks and can be consi(iered to be the result 01 the 11m1tect reepon6

ot the m:l.crodevices to porosity which is no t aS80ciated with pemeabil i t , . re.lCM11l1e, in la zeme with small non"1nterconnected vugs and which perhapJ"has s1dtrgranular porosity, the microdevice will detect only the conditiOns in th1 D ~ . t g r a n u l a r poroeity while the Nutron or Sonic logs will be m e a s ~ g to tapO"otii,.. I t i s clear then that a calculat10n trcm Figm-e 1 would indieate higRaS .ven tbough the vugs may be completely filled with water. 'l'he apparent ~ it.h1a wstance may be considerad to be related to the tortuosit, . ot th'; rock an8l1b\ld. theretore, be correctly indicative of the pemeabi11ty c o n d i t i ~ l l s . .II.- ' ,~

"- ..... 1000"".~ ""'" ..............." '-O .' . .. - . - -_ . . . . . - """" . . . .. .. -- .. ----" 1)-' --_--00- _ ... . - . .-~ .,K .... ~...._- .............---- ......- ........ 1 .. ~" , ~I.n

" ....." ,\. \\ \"- ,0.1 \ \O 10 20 30 50 E.Q 70 80 SIO leAPPARENT ROS (%)

F i g ~ 2 - RaSa -Pe:nneabUi y Correlation - San Andres3


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The solid line in Figure 2 ia a curve resulting trom a plot 01 tbe appent ROS va permeability lrom a limited number o data points from tbe San ADdtomat1on in West Texas. 'fhe apparent Rre values vere determinad trQm figureusing R.m values trom the Microlaterolog and porosit)" values trom wholecore . .ses. '1'he permeabilit)" values. are averages o t12 maximum and 900 air pe1'lJe&b1ties recorded in the core analysis reporteContormance 01 the data to the curve in Figure 2 :1s good betveen:the rangot permeability trom ,0 lid to .3 md and ranges ot ROOa traa .10 to .80 Where tconnate vater saturation is less than 2, per cent and vhere permeable Iones aresutt1cient thicmess to aUow proper resolut.ion ot the logs. "

EFFECT OF CONNATE WATER SATURATIONThe above relationship neceasaril1' applies onl.y to zmes o rl,ftivelT l, connate water saturation. Obviousl1', in a predaninate1y _ t e r til1ea>lcne, trelddual oil aaturation wiU be low regardless o the permeability.::. In tacnear the oil-water contact, zones ot low penneabilit1' can be e:xpectecr"to have lres idal 011 saturations due to capillary forces. Zones ot high 1 t a t e ~ \ e a t u r a t 1can usuall1' be detectad by calculating the water saturat10n using ~ h i e ' s tollUl.a and data rOll the Laterolog or Guard log. Permeab1lity c o n d 1 t i ~ n s in thesones, hovever, are not important to the evaluat10n ot a veU's p ~ u C t 1 v 1 t , .iba,. are usually vater prodootive. Although conformance 18 not gooclj:'tbe dotline in Figure 2 representa an average curve tor water saturat10he lreater tb2S par cant. No deinite deviation trend vas noted for variat10ns 1Pvater aaurat10n vhere the value s o water eaturation vere low because ot th eftect+be p.trophy'sical characteristics o the rock on theae va1uas. .

APPLlCATIONThe applicat:1.on o this techn1que can be 1llustrated t h r ~ ~ h ..:the UNeD1llples. 'fhe examples used will represent vella ot three types t ( l ) a ...which produced with a high 011 rata and 10w water rate aftel' t r a c t ~ , (2)ve11 which prodmed water trom one zone alter stimulat10n and , p ~ u c e d 81&aaounis ot oi1 and water rom another zone alter f'racturing and (3) 1.".U whproduced 100 par cent water w1 thout stimulat1on.

?!!!p1e 1Data trom this vell are tabulated in Table l . Th1s ve11 fiOWd'. alter tiaturing at the ra teo t 36.6 barrels ot 011 per hour with no water. ~ t e l ' f t l . No.01 th1s ve1l i8 ot particular interest in tbat a RelSa ot. O per cent li; c a t A a'1'h1s value 11&)" be indicative ot two reservoir conditionst (1) . ;';tracture

large vug wh1ch ia comp1etely tluahed or (2) a thin ~ o n e vhich dl4 nOto aUow CCplete reso1ut10n ot the poros1ty measuring dertce. E1ther candition ~ ~ u 1 d also,responsible o r the h1gh water saturat10n val\8 indioated. Tbere 18 " ~ 8 ( 1 ) . to blieve that such val\8s ot RC6a ma1' al80 hin t 01 poor _ter-011 ret4:tive periabi1i y condi 10ns in the part1cular zona. .IDiaple II

Data troJll this we11 are shown in Tab1e 11. 'l'he zonea in thia vel1 bAbean divided into tour groups. Group I II vas the t1rst group to b. tested.4


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e:xpected trom the ca1culated water saturation and permeabi1itr, this group produced 100 per cent water atter an acid treatment ot 3,000 gallons. The dottecurve trom Figure 2 was used in estimating K for this group.Group 1 was then testad. This group p r o d ~ e d no tluid prior to stimulatio

and, produced a total ol 1,329 barre1s of oi1 and approximatel1' 7,000 barrels ow a t ~ in 15 months following a fracture treatment. I t 1e pointed out that fiel. ~ r 1 e n c e has ehown that i t is extremell rara that aigniticant production is obtained trom zones where some permeability is not indicated by this method, evethoUgh these zones are subsequent1.y fracturad.. Due to operationa1 difficulties and the marginal possibilities of Group 11

i t n I not testad. This group would probabll have produced some oil with a watecut att.r fracturing but would not have justified the cost of recompletion.EJimPle 111

Data tran th1s vell are shown in Table 111. This weU was clasaified aswiUQ't. Calculations of connate water saturations 1ndicated tbat the well woulpOllibl1 p r o d ~ e 011 with a large water-cut. Good pemeabilitles vere indicatetrbJI the veU log data. The ve1l testad at arate ot 9 barrels of water per houw1ihout a trace ot oil . As mentioned betore, values ot ROOa of the order indicaeel here iaIq be s1gniticant in predicting the behavior o the va11 wi h regard ttha wat.er-oil ratio.

aI'HER CONSIDERATIONS!.nere are factora othar than tbose discussed which Should ba considered imald.b, iD evaluat.ion o this type. One factor ia the etfect ot 'f/ery thin permabUit,4evelopaentl or fractures in non-conductiva rocka on 'falusa read frem th

lO,.. !he microdevice. wUl have a tendency to investigate deepar tban the RxIon. reading Ri or perhaPI Rt. At the same time the porolltt maasurlng deviceViU a.eraga the porosity over the zone. Fortunate13, the tvo cmditiOlls tend tott.. .ach other in their effect on calculatlons 1n an oU lone lDd. wiU accenthe ):)te8ence of vater in a vater zoneoAs ls trua in other quantitative uses of weU log data, the importance oobtaiJ1ing an acourate poroslty measurement cannot be ovar amphaailed. Not only lthil the Dloat iJIlportant measurement to be made but perhape tbe most dUficult'l'h. Srdc log se81llS te ba tlle baBt approach to thia problem il be San Andres tormatioD a t the present time.Sitlce the curves used in th1s diacWllion are empirica1 in nature and deriv

ee! from data obtained from the San Andres fomation in Weet Texaa, thet should b.. i t ied by a largar study betore their appllcat10n 11 extended to other format1

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SUMMARYThe use o calculated values o' the residual 011 saturation in the lluShed lone around the we11 bore as a key to pemeabU1ty determination in an.011 produoing zone 1s simple and can provide quantitative valuea o rook pemeabilitwhich are he1pt'ul in predicting we11 pert'ormance. Curves such a8 the one show

in Figure 2 should prove he1plul in making rapid evaluat10D8 ot re.. voir permeability from well log data. Care should be taken to proper],y eval18te coJlditionwhich l imit the accuracy o ' the measuring dartce. or natural oondi t ion 8 in thereservoir which mAy attect the calculations.ACKNONLEDOEMEN'l'

The aut.hor wishes to thank Mr. D. E. Hockaday tor his helptul s u g g e e t ~ o n sin pre:arat1on 01 this apere

REFERENCESlo Doll, H. O., The Microlaterolog, .Petroleum Transactiona AIME", Vol198, 19S3, po 27.2. Pirson, S.J. , Formation Eva1uation by Log Interpretation, "World Oi1" AprU, 19S7.3. 'Winsauer, Shearin, Masl!IOn and WUJ.iams, Resiativity 01 Brine-8aturatedSands in Relation to Pore GeOll8tl'1, "BuUetin 01 'lhe American Associat10n o Petroleum Geologists", Vol. 36, No. 2, Feb., 19S2.

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TABLE 1ELDER NO. 7

~ BmInterva1 Rt Sw th Km J;t B(S K lb- - - - -No. Ft.-1 5 125 24.0 9 45 17 5S0 S2 S.8 29.2 4 115 14.h 15 60 11 3S6 6S 2.9 11.3 10 11S 18.8 12 120 11 3% S2 S.8 S8.4 4 192 17.7 10 40 18 S80 59 4.0 16., 3 40.4 20.0 19 ,7 6 19, 62 3.S lO6 4 115 20.5 11 4h 10 325 50 6.4 25.7 2 29.4 55.5 8 16 4 129 O SO.O 100.8 8 66.2 21.2 14 112 7 226 51 5.8 46.9 2 99.6 24.2 10 20 21 680 62 3.5 7.

10 4 66.2 29.7 10 40 21 680 62 3.5 14.11 8 116 28.0 8 64 18 580 50 6.4 51.12 4 u6 22.4 10 40 25 810 65 22 11.Total 58 658 380.Rw = 058 On potentia1 atter fracture, velfloVed 100.66 BO aD4 no vater 111Rmr = 031 2 h ~ l . 45 mina. through 28/64"choke.Average 11.3%Average K 6.6 md.Average S. 23.1%


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TABLE 11UNlVERS!TY "O" NO. 1

Interva1 lit Sw (JI Rxo RxoBit ROO 1 Kh- - - -o. r t.1 6 210 50.0 4.2 ::>50 .1* .2 .3 286 43.2 4.2 >50 .1

l . .3 2 828 24.8 4.3 45 1250 32 2.0 4.4 4 550 31.0 4.2 >50 .1* .5 4 550 29.2 4.5 >50 .1* .6 4 148 49.0 5.0 38 lOSO 48 .7 2.,7 4 165 23.7 10.5 3S 97S 70 2.1 8.8 3 165 23.7 10.$ 2S 695 61 3.7 U.9 6 148 23.8 10.$ 27 7SO 6S 2.8 16.

I I . 10 4 92 32.0 10.$ 1$ 417 $2 .h 1.11 6 92 42.11 7.$ 18 $00 40 1.2 7.12 3 70 30 3 12.0 10 278 SO .S 1.13 3 50 43.0 10.0 12 333 46 .7 2.14 4 32 SS.o 9.8 6 167 20 3.0 12.nI. 15 4 65 38.4 9.8 14 389 48 eS 2.16 4 16.7 71.0 10.5 3 83 O S.O* 20.

IV. 17 6 18.4 59.0 12.0 4 III 20 3.0 18.18 6 25.1 52.6 11.5 6 167 30 2.3 13.Total 76 123.Bw 0.092Bmt : 0.036AV8rae t = 8.6A.verage K 11 1.6 md.Average 8v 11 41.5%* Eatimated


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IntervalNo. !1:.1 22 33 64 85 46 107 4

Rv 0.06Rtat. .Oh

Rt46.246.016.720.033.310.013.3

TABLE I I ImnVERSI'I'Y nsn NO. 1

s" e Rxo36.1 10 836.2 10 14150.0 12 252.1 lo! 329.1, 14i 348.4 16 1146.4 lb! 2

RxoB;t ROO K- - -200 305ao 60 .250 o75 o75 2038 oSo o

*hi le tl'B H 10De. oannot be alligned a pe:nneab111ty value, 1t 18 c l . r that thpermeabill'ty ie euf1'ic1entq hi,h to prod\ee nuid.

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A Method for Determining Permeability From Well Log