SPE 13894 A Comprehensive Fracture Diagnostics Experiment. Part II. Comparison of Seven Fracture Azimuth Measurements by M. 8. Smlth,*tAmoco Production Company. N.-K. Ren,' Dowell Schlumberger, G. G. Sorrells,' feledyne Georech and L. W.Teufel,* Sandie National Laboratories '

WImbrr SPE-AIHE

ABSTRACT

A great deal of e f f o r t has been devoted recenttj t o f l n d geophysical techniques f o r measurlng tht hydraulic fracture azimuth. This paper discusses I capar ison o f seven d i f f e ren t measurements used t t detennine the rz invth I n 8 sandstone formation at 4 depth of 1,000 ft (320 m). The azimuth was deternlnec as N95E, but s ign i f icant differences tx ls ted betweer some o f the results. Thls I t o f fundamental Impor. trnce Slnce I n developlng MY wasurments, the l l m i t r of these must be found and honored.

Of par t icu lar Interest are the resul ts fron microseismic monitoring. The lack of results suggest! that remote (e.9.. surface) monitoring f o r selsmti events may be Impractical f o r nonnal , sedlnentary, hydrocarbon-bearing fonnatlons.

IWfRODUtTIOW f o r many years It has been accepted, and verlffec

by research, that hydrrul lc fractures rre generall j vert ical , and extend from the w l l b o r e dong 8 Slng14 azimuth. I t was also noted; that planar features, such as f rac tu re , can s ign i f i can t l y a1 t e r reservoir f l u l d flow. However, l l t t l e at tent ion was directed t o t h i s problem u n t i l the development of Uassiue Wdrau- l l c Frrctur lng proved a vlable technlque fo r producing low-pcrmeabfl l t y gas reservoirs. f o r these mmlcro- darcy' fomstions, f racture lengths greater than noms1 drainage rad i t are j u s t i f l e d 0- making It necessary t o deternine the fracture azimuth p r lo r t c d r l l l l n g the l n f i l l wells which w u l d make I t possible t o detennlne the azlmuth using pressure t r r n s l t n t analfifS, such a t discussed In Clnco-Ley.2 I n N- sponse t o th ls , several geophysical techniques have been developed.

References and l l l u s t r a t l o n s a t end of paper. tCutr tnt ly uith llolte-Smlth b Assoclater

These Include core ana lyse^,^***^*^^^ surface tilt measurements,@ e lec t r i c potent ia l measurments9 and Seismlc nonl tor lng fo r aicroseismlc events related t o the propagating fracture.ioBil For each procedure, there ate severdl references rhowlng that lnterpret- able Slgnals, or data, Can be recorded. There are less data where several resul ts are canpared and t h i s I s unfortunate since several techniques are ind i rect , or base t h e i r r n r l y r l r on rssumptions about the phys- i c r l process creatlng the signal. Thus, It should not be expected that every procedure can work i n every case; f o r example, monltoring f o r microseismic events I n a poorly consolldated fornation would probably not y l e l d good results. One older reference i n CO10radO'2 and more recent tests I n Colorado and T e ~ a s 1 3 * ~ * have CCmpatcd several technlques with generally good agree- ment; however, a l l o f these tests #re ConduCteC I n s lmi l r r fonnations - re la t i ve l y deep, hard, lou- porosity sandstones.

Thls paper reports the resul ts from seven d i f - ferent azimuth measuring procedures conducted as part o f an hoco/Dowell Schlumberger/tas Research Inst i tu te f racture diagnostics test. The test was conducted i r the Skinner Sandstone near bunds, Oklahoma. A t this location, the formation was found a t a depth of 1,OS: ft (320 m), with a thickness o f about 80 ft (24 m), porosl ty of 25%. average penneablllty o f f l v e nl l l l - darcles, 1002 water ssturatlon, and nonnally pres- sured. Slnce the prlmary goal o f the experiment was t o measure proppant trmnsport, the test was conducted I n two stages by f l r s t measuring the fracture azimuth t o allow optimum placement o f surfact magnetometers f o r subsequent arapplng of magnetic propprnt i n jec t ion.

The azimuth measurements Included on-site and lrboratory-orlented core analyses, t i l tme te r measure- ments$ downhole te lev ls lon camera logging, remote S t l M I I C monitoring, borehole stlsmic nonttoring. and ca l lper logs for wellbore %reatouts." Table I sum- narlzes the results. Uhlle excellent agrement be- tween borehole logs, tiltmeter rna ly r i s and s t ra in recovery measurements on core concluslvcly shows I n essent ia l ly east-west rzfmvth, the disagrerment i n one SCnSC IS good, mphaslzlng the wed for mult ip le tests I n a n e w area or f o m r t f o n t o guard rgainst mlS1eaQjn9 r tsu l ts .

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

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A COHPREMNSiVE FRACTURE DIAGNOSTICS EXPERIWENt. PART 11. COnPARISON

CORE UULYSlS helrst tc Strrfr kwcry kthod

through the Instrument array.

. . 'C ' .

Flve cubes (rpproxlmately 3.2 on on a r lde) were prepared f o r OSCA tests and the three mutually per- pendlcular faces on each w b e were Instrumented wlth r t r a l n gages. The smplts were then subjected t o hydrostatlc loadlng t o 125 Wa. Straln and pressure were c l c c t r o n l c r l l y logged and the accuracy o f the s t ra ln measurements was 22 mlcrostralns.

S I X dodecahexahedral specimens (rpproxlmately 4.5 an on a r lde) yere r l s o prepared f o r WVA testlng. Canpresslonal waves were transml t t ed through the sample I n nlne directions and velocl t ies were recorded for rnalysls. The accuracy o f the trrvel- t ime nea- suranents was 9 . 0 2 usec.

The OSCA and DWVA resul ts rre sumnarlted i n Table 3. There I s basical ly a good agreement on r t imuth predict ion between DSCA and DUVA. However, the re- su l ts were not conslrtent u i t h other technlques used I n th l r study. Consequently, t h l r encouraged further lnvest lgat lon o f structural features I n the regfon. The fol lowlng dlscusrlon I s based on the tcctonlc structural features and the con f l l c t l ng resul ts fran the d l f fercnt techniques .

OSCA I s a r e l a t i v e l y new technlque, used t o 0 There are no major preexisting l n -s l t u micro- determlne the spat ia l or lentat ion and r a t l o of the cracks. pr inclpal stresses. It I s based on the arrunptlon that a rock core, r t t r l e v t d from I t s dounhole confined I n general, the number o f alcrocrrcks Induced at condltlons, w l l l expand In proportion t o the changes the t lw of corlng rnd the degree o f contrast (abso- I n applled stresses. This cxpanrlon occurs I n part l u t e ragnltude) mong ghe three pr inclpal stresses because o f randanly oriented microcracks tha t are w l l l Increase as the depth Increases. This means that Induced o r reopened upon removal from downhole con- the resolut lon o f the technlque I s f r c l l l t a t e d as finment. Stralns atsoclated with such aicrocracks depth Increases. are r l l t g e d t o be lnd lcat lve of the stress dl f feren- t l r l (l.e., the reduction of stress upon unloading HOwcver, the umplcs studled here are very shal- from tn-sltu condltlons t o Ilnblent condltlons). low rnd, as such, present unlque problms t o the Therefore, by submlttlng an o r l cn t td rock speclnm t o ln tcrpretat lon of DSCA data. The p o s r l b l l l t y of other Irydrostatlc n load lng under laboratory conditions, the types of microcracks or aacroerrcts, such as Pre- d l f f e ren t l a l r t r a l n observed I n vrrlour d l r t c t l ons ex is t ing j o i n t sets or dma e from r c h a n l c a l handling rf l l k a t some relat lonshlp t o the preexlstlng down- ' interferingo wl th the resu!ts. I s great ly enhanced I n Role condltlons. The prlnclples, t t s t l n p proctdures umplcs from t h i s depth cange. Thls Is a canonly and Mpar i sons rrith other measurements can be found encountered problan rnd w r i t s saw fur ther discussion i n Strlckland and Renr6 Ren rnd Rocglers2" and I n t h l s InStanCe.. bntgOmery and Ren.2s

or lentat lon 8s wel l as r a t l o of the pr lnclpal stress stone. Canponents. It i s based on the same 8SSumptlonS about

DUYA, l l k e DSCA, I s used t o detemlne the spat ia l The Skinner Sand I s a r e l a t l r e l y so f t sand- Thin sectlons n r e prepared and ana ty rd for

any obvious sign of preexisting microcracks. Howevere

SPE 19894 )1. B. PlITH. N . 4 . E N , 6. other I n the hor l rontal plane of each con. r)H ve r t l ca l s t r a l n was measured by llountlng a gaugt p r r l l e l to the u t l s o f the con, Dlsplrcanent datc f o r each gauge, roan tmperature rnd the c o n tempera r t u r e e r e recorded every hour. 01s lrcce~lents weft

settlng, m d the aagnltudes 8nd o r l cn t r t l on r o f the pr lnclpal hor l ronta l s t ra ins and the ver t lca l s t ra i r magnltude e r e CrlCUl8ted from the teinperature-cor= rected r t ra ln data. For t h l s f i e l d test, the rccurac~ o f the straln wasurements #re 22 mlcrostralns.

thc a n e d t i c s t r r l n rtcovery wasurments 01 orlcnted core I n the bunds t e s t -11 are sumnarltec I n Table 2. M e aaxlmun horlzontal s t r a l n ( s t n s s ) d l n c t l o n ranged from M9.E 28' t o WM*E No, t d t h I aean or lentat lon o f 186.E $14' f o r a l l four cores, The range I n er ror o f the naxlmm stress d l rect lon car be at t r ibuted t o both the s t ra ln measurement ttchnlquc and the or lcntat lon survey o f the core. It should k notcd that the error associated wlth the stress dfrec. t lons determined for the tm measurements made I n eac? of the coring t r l p r I s much nduced, wi th the near direct ions having an error of less than seven de- grees. f i l s suggests that the range o f error In the stress dlrect ions I s due largely t o the error of thc core or lentat lon survey. The core or lentat ion survej I n t h f s experlment was done as w e l l as posslble u l t t ex ls t lng technology. Accordingly, the accuracy 01 core or lentat lon surveys may be the l l m l t l n g factor I f uslng s t ra in recovery measuranentr t o detemlne ths hydtaullc f racture azimuth, However, It I s r lsc lnterest lng t o note that resul ts fran the second cor4 r r e In perfect agreement tdth dounhole te lev ls lon log4 8nd t l l t raeter surveys. Since the f i r s t core wa$ recovered under extremely adverse weather conditions, It may be that resul ts on the second core more accu. r a t e l y represent the type of resul ts tha t can k achieved under Ideal conditlons.

Further dlrcusslon o f the these aeasuranentr and stress magnltude calculat ions us ln the s t ra ln re-

converted t o s t r a l n frm the I n l t l a e gauge tengt!

covery data are presented i n Teufel. 6(2

D l f f e n n t l r l Strrln Curve k r r l y s l s f e r t n t l r l Y v e Veloclty h n a l p l s

!. SORRELLS AND 1. Ye TEUFEL C ~ U S C S o f microcrackin as I s DSCA. Analysts I s sinllrr t o that used #or N C A except tha t canpres- rlonal rcour t lc wave reloel?#, rather than strain, 1s n a t u r e d I n DNA. The ve loc i ty Of a canpresslonal uave I n a rock speclmen ut11 decrease If r p p r o p r l r t t l j orlcnted RICrOCrrCkS exist, and the degree of re loc l tJ var la t lon I s proportlonal to the denslty o f micro- cracking I n r specl f lc Ulnct fon, Therefore, br submlttlng an oriented rock specimen t o hydrostatic n load lng under laboratory condltlons, the differen= tirl uave re loc l t y observed I n varlous dlrect ions ul11 bear a re l r t lonship t o the preexlst lng downhole stresi condltlons. The prlnclples, test lng procedures anc some prellRlnary resul ts can be found I n Ren anc Hudson .'

I The major 8ssumptlons for OSCA and DUVA include the followlng. a The nlcrocracks ere induced i n the core m a t r l x

as the rock expands In response t o the release of l n -s i t u stress durlng corlng.

A COWREHEWSIVE FRACTURE DIAGNOSTlCS EXPERIMENT. PART 11. COnPARlSON 4 - OF SEVEN FRACTURE A no ae f in l t l ve cletermlnatlon was possible. This I S not surprising conslderlng the postulr ted dlaenslons of induced i i c m r a c k t . HOwevere the n l a t i o n s h l p k- tween the gross tectonic Structural n g l m and the n s u l t s of t h i s m d other stress or lentat lon studlet n u e s s l t r t e s fu r the r discussion.

Structural history o f eastern Oklahana indicates I l i ke l ihood f o r the raxllnun horizontal Drincipal stress U l r u t l o n In &e e t rocks t o be oriented i p - proximattl n o r t h T o + sout t b o Y (evidenced by the thrust f r u f t l n g around &xhlt8 County, Figure 4). stress U l r u t l o n In &e e t rocks t o be oriented i p - Droxlmattlr n o r t h T o + sout t b o Y (evidenced by the thrust f r u h l n g around &xhlt8 County, Figure 4).

However, i n the shallower racks, the aaxlarn horizontal stress d l rect lon may s h i f t t o kcome the mlnlmum horizontal stress d i rec t i on owlng t o the relaxation (evldenced by the notma1 fau l t i ng rround Wuskogee and Wagoner Counties, Figure 4) occurring a f t e r cessation o f the forces responsible f o r the Ouachita thrusting. Thls relaxat ion would make the arlmuth o f the raxlmum horlzontal stress l i e between E160.E and east t o west a t shallow depth (where It 1s postulated that stretching of the rock layers occurred over the Ozark Upl l f t ) .

Several technlques, rl ready discussed, have indicated the maxlmum horizontal stress azimuth a t N85.E ~ 1 0 ~ . These predictions are consistent wl th the interpretat fon o f tectonic and structural informa- tion. It seems possible that the nason DSCA d id not detect the 'shifted" stress f l e l d may be that mlcro- cracks *re Induced during the period o f I n -s i t u tectonic stress relaxatlon, and that these microcracks 'Interfere" d t h laboratory DSCA and DUVA stress state determinations (especir l ly with aeasurments made a t pressures greater than in-si tu confining pressures) . I n fact, i t would seen tha t the gross stress f l e l d (without the e f fec t o f shallow depth relaxation) was detennined by these trro techniques due t o the presence o f mlcrocracks f o m e d p r l o r to the coring operrtlon.

The depth t o which t h l s 'relrxation" has al tered the i n - t l t u stress f i e l d i s not clear. It m u l d be interest ing t o have a complete evaluation of i n -s i t u stresses (or ientat ion and magnitude) from the surface t o a consider&ble depth, such rs 3,000 ft, in order t o lnvet t igate the stress prof i le . A de ta i l discussion o f DSCA and bYVA resul ts on t h i s s i t e can be found i n a 1984 Dowel1 khlunberger Ueport.26

Research connected wlth cvaluatlon of 'hot, dry rock. geothermal resources has denonstrated tha t I n grani te rocks, hydraul IC f r r c t u r l n g lnduces ueak aicroselsmlt r ~ t l v l t y ~ ~ r * ~ d t h s lml lar phenomena observed f o r treatments i n welded t u f f s and, more rectntly, i n l en t i cu la r t i g h t gas sands.28 The sources o f the r c t l v l t y c luster I n a roughly tabular zone surrounding the fracture, rnd thus estimations o f the s p a t i l l d l s t r i b u t l o n o f the mlcrosetsmic sources provldes 8n rpproximate map o f the frrcture. I n order t o fur ther study and quantify the value of t h i s pro- cedure for sedimentary rocks, t h i s experiment included the we of various u i s t i n g microseismic methods t o dcflne the r r imuth rnd g e a c t r y of the hydraulic fracture.

The i n i t i a l goal ws t o wqu i re quant i tat ive data about the s t a t l s t l c r l properties of treatment-induced mlcroseirmicity m d the seismic background nolte

lMI.!TH MEASUREMENTS SPE rssociated d t h c n a t l o n of a hydraulic fracture? sedlmentarv rocks. This infomat ion rrrruld be used t o evrluate ?he technlca7 f e a s l b i l i t y of devtioping advanced 4nstrmcntatlon which would u t i l i z e t rcat - Rcnt-induced microseismicity to ~ a p hydraul IC frac- tures. To acquire the desired data, a test was de- signed to seismically monitor the b d r a u l i c fracturing a t t h i s tes t slte. To tnsure rdequate coverage during the treatment, r n extensive rrrry o f stlsmic sensors was deployed both a t the surface and i n observation wells u f t h i n 1,OOO ft (320 a) of the treatment ell (see Figure 5). the sensor array configuration u t i - l i zed f e r the tes t included the followlng.

1. A conventional microearthquake monltorlng network consisting o f nlne t r l a x l a l Seismograph systms d ls t r lbuted more or less randomly wi th in r 1,000- ft radlus c i rc le .

2. Tu0 l i nea r horizontal r r r a s o f exploration geophone groups, each $00 ft !n length, implanted on the surface along perpendicular l i nes In tcr - SeCtlng at the wellhead.

3. An array of exploration geophone groups located along an a x of a c i r c l e wi th a 750-ft radlus centered on the treatment well.

4. Two l l nea r ve r t i ca l arrays insta l led i n observd- t l o n wells SCIO ft from the treatment well and extendlng f ran about 30 t o 500 ft I n depth.

The deslgn goal f o r the horizontal and vcr t lca l r r rays was t o detect signals fran nicroselsmlc sources roughly 10 times weaker than the publlshed strength of sources stimulated by treatments in granites during 'hot, dry rock" experiments.

Analysis o f the data recorded durlng the experl- Rent demonstrated that the design goal was not only met but was exceeded by a factor o f two or three. Nevertheless, despite the re la t l ve l y hlgh s e n s t t l v l t j o f the monitoring system, no obvious alcroseismic signals were detected e i the r by the arrays a t the surface or i n the observatlon wells. )bwever, there was evidence o f creak, coherent, selsmlc energy prop- agating a t apparent ve loc i t ies appropriate f o r source3 near the fracture, occaslonalty observed on processed outputs o f the uer t tca l arrays. Furthermore, selsmlc data, recorded 4ntetmlttently i n the treatment w e l l during shut-in perlods, provided h3Uitional tvidcncc o f weak relrmic act iv i ty . Taken together, these observations imply t h a t the hydraul IC fracturing treatment a t the ?bunds experlment Stlfaul8ted nicro- selsmlc r c t i v l t y wl th maximum signal strengths a t of near the detection thresholds of the monitoring sys tmt .

The strength o f r seismic r lgnal i s proportlonal t o the ament, , of i t s source which I s a convenlent ulated by s iml l r r processes l n two d l f ferent geologlc aedine The published values of % f o r the aicro- s t i ah i c a c t l v l t y observed during the "hot dry rock' ex r inents I t Fenton H i l l , U e w lkxico, were about loP: dyne-cm;* whereas, the ind i rect evldence ci ted above lndlcates t h a t the aax lam strength of the a i c rose lm ic r c t l v l t y stimulated during the Wounds expctlnent ws only about 3 x lo12 dyne-an. Further cmparlson o f i a e n t data frm bunds rnd Fenton H I l l Z s u l t h reference t o m p l r i c a l data presented I n Kanmoriso and theoret ical considerations prcscntcd fn

parameter f o r "SRI c paring mlcroselsmlc a c t l v l t y stim-

' . c . .

SPE 23894 H. E. S I T H . k - K . REN. 6. Tr l~unac ,a1 strongly suggests tha t the n l a t l v e l y lm source strengths o f the selsmlc a c t l v l t y s t inu lat td during the treatment rt )bunds can be la rge ly a t t r l b - uted t o the low i n l t l a l shearing stresses i n the Sklnner Fomatlon, l h l s resul t has lnportant pract l - ca l tapl tcat lons wlth regard t o the f u t o n use of surface-based w n l t o r l n g systems t o detect mlcro- sclmlc act lv i ty .

Spcclfically, the apparent absence of t l gn l f l can t tectonlc rhearlng stress canponents l a the Sklnner Sandstone, the antlclpated slgnal mp l l t ude decllne with 8n lncnase In depthzs 8nd the observatlon that slgnals *re only aarg lna l ly detectable a t Hounds, suggest t h a t nlcraselrmlc aonl tor lng a t c a n e r c l a l depths wrlng turface-based Sensor systems uill be unsuccetsf ut unless

e the shearlng stresses I n the candldate fonua- t l o n are substantial; o r

0 s lgn l f lcant reductlons i n real I rable. slgnal detectlon thresholds are made through the use o f Improved instrumentation and aSSOCf8ted s lgnal processing.

The overal l outlook f o r rurface-based nlcro- relsmlc monitorlng methods I s pesstmistlc.

However, It I s posslblc t o circumvent the signal detectlon problem e n t l r e l y by I n s t a l l i n g the sensor system near the fane undergoing stimulatlon. I n most pract ica l sltuatfons, t h l s means that i t must be placed I n the treatment w e l l near the upper or lower boundary o f the fonnatlon o f Interest. Thls ap roact uas ploneered by Sandla Natlonal LaboratoriesP' and presumably has been developed t o the polnt where I t can be used t o provide re l i ab le f racture azlmutt c s t l m a t e s , ~ ~ One o f the souls o f the Mounds experla ment was t o provlde an Independent assessment of t h i l method. In order t o sa t i s f y t h l s goal, a subcontract was l e t t o Fracture Technology, Incorporated, t c acquire mlcroselsmlc data durlng shut-In periods 01 the l n l t l a l water I n jec t i on stage o f the treatment, I n addltlon, they were authorlred t o provide an e s t l - mate of the f racture azimuth uslng the analysls aieth- ods developed by Sandia National LabOr8tOrleSe An Independent analysis o f the data was perfonned by Telcdyne Geotech. The resul ts o f th ls analysis, whlch w l l l be reported I n de ta l l elsewhere, raise rerlous questlons about previous lnterpretat lons of the seismic data recorded In treatment wells. In par- t lcu lar , It was found tha t few, I f any, of the ob- served signals could be unambiguously i den t l f i ed as t i ther d l rec t compressional o r shear body phases. Such an l den t l f l ca t l on I s fundamental t o the Sandia approach t o f racture arlmuth tstimatlon. Woreover, the slgnals tended t o be strongly po lar l rcd a l t h both l l n c a r and e l l i p t l c a l pa r t i c l e motion o rb l t s (F lgun 6). k ld l t l ona l l y , the mp l i t ude spectra o f the rig- nalS uen found t o be CharaCterIted by nunerous sharp peaks. These are propertles which are more t yp l ca l l y r s r o c i e t d with waves tha t are .trapped" In a setsmlc uavegulde, rather than d l rec t compresslonal end shear body phases, Final ly, it was found that the rzlutuths of the l l n e a r l y po l r r l ted, u i t h l n the l l m l t s o f cx- perlnental error, are not distingulshably d l f ferent from the rpparent f r r c tu re atlmuth reported by Frac- tu re Techrol o ~ y , Incorporated (N60E). These rcsul tt suggest t ha t those components o f the selsmlc slgnals observed i n the treatment wells, whlch have been ident l f led as compresslonal waves i n previous Inves-

SORRELLS AND 1. Y. E U F E L t lgatlons, i l g h t well be l l n e a r l y polarized, trapped modes that are character lst lc o f a wavegulde whlch I s functtonally related to the c n a t i o n o f a hydraulfc fracture. This poss lb l l l t y I s current ly under Inves- t i g a t l o n and the resul ts o f that study w i l l be re- ported a t a l a t e r date.

cowcLus10I(s

The pr lnclpal conclusions t o be drawn from thr passlve selsmic experlaents a t (bunds nay be rum- aar l rcd as follows.

The w e o f selsmlc methods which require surface- i ns ta l l ed sensor systems t o monitor hydraul l c fracturr treatments a t c m e r c l a l l y lnterest lng depths I! l l k e l y t o be successful only i n those rpeclal case! where the shear stresses i n the formation undergolns treatment are RUCh larger than those caused by thc overburden load. Since t h l s conditlen I s not l l k e l j t o occur on a wldespread scale i n oil- and gas-bearin! foraatlons, such methods cannot be expected t o play 4 s lgn l f lcant ro le I n rout lnely detemlnlng the arlmutl and dlmenslons o f hydraulic fractures. On the other hand, seismlc methods whtch use sensor systems de. ployed I n the treatment well have the potent ia l foi providlng re l l ab le estlmates o f the fracture arimutt on a rout lne basis as w e l l as estlmates o f othei hydraulic f racture parameters o f Interest. However, t h i s p t e n t l a l cannot be f u l l y rea l l ted u n t i l un- cer ta ln t les about the nature o f the slgnals observec I n the wellbore have been resolved.

The fracture atlmuth at the tes t s i t e was deter. mined as True N9SE, as measured from the wellborc atlmuth (using a downhole te lev ls lon camera). tilt. meter oonltorfng and s t ra in relaxatlon measurements However, the important conclusion relates t o thc d i f f e r i n g resul ts from some o f the procedures. Spe. c l f l c a l l y , DSCA and DUVA analyses, I n t h l s part lcolai sltuatlon, are a l r r o r s o f paleostress regimes canbfnec wfth the current regime.

I n developing MY techni ues, It I s important t c determine, and honor, the ~ l m i t a t i o n s o f various measurements. The lack o f d i s t i n c t nlcroscismic events Indicates that there may be a shallow l i m i t t c seismic aapplng. Cor depths above thls, there nay be l nsu f f l c l en t Strain energy stored In t h e rock t c create measurable slgnals. Thls could also be ol concern i n overpressured reservoirs where the port pressure 1s su port lng the overburden, leavlng l l t t l c

Uhl le I n one sense borehole seismic dld yielc resul ts close t o the correct rrlmuth, It should bc noted that f o r f racture azimuth measurements, 30. I s I t l g n l f l c a n t error, Thls i s eas l ly seen fo r a square w e l l pattern, where 45. I s the m r s t posslble error.

energy stored P n the rock.

Another general concluslon relates t o core anal- y s l s for detemlnlng the hydraullc f racture azlnuth. When corlng Oper8tlOnS a n scheduled f o r other pur- poses, the additlonal 8n&lyslS required fo r the rr lmuth tests I s mlnlmal. Also, r lnce corlng I s normally done ear ly I n the l l f e of a f ie ld , the In- fomat lon I s very tlmely. However, the analysis of cores 1s based on rssumptlons about the Internal defomatlon character lst ics o f the rocks. flncc these nay (almost cc r ta ln l y w i l l ) vary from cock type t c

A COWREHEMIVE FRACTURE DIAGISDS

Snith, n. 8.. h b a n , 6. 8.s Fast, C. R., and Colvln, R. 3.: "The k l n u t h of Deep, Pcnctratlng Fractures I n the Mattenberg Fhld,' do Prt. Tech. (Feb. 1978) 185.

Teufel, 1. Y., Hart, C. kD Sattler, A. R., and Clark, 3. A.: 'Determlnatlon o f Hydraullc Frac- t u r e k l a u t h by Gcophyslcal, 6eologlcal, and Oriented-Core )lethods 82 tbe M u l t l w e l l Experlrnent Slte. Ri f le, Colorado," paper SPE 13226 presented a t the 1984 SPE Annual Technlcal Conference and Exhlbltlon, Houston, k p t . 16-19.

Lacy, 1. 1.: .Canparlson o f Hydraullc Fracture Orlentatlon Techniques,' paper SPE 13225 presented a t the 1984 SPE Annual Technical Conference and Gchlbltlon, buston. Sept. 16-19.

Smlth, I!. Be, Rosenberg, R. 3.. and BOWn, J. F.: 'Fracture Yldth, Deslgn vs. kasurement," paper SPE 10965 presented at the 1982 SPE Annual Tech- n lca l Conference and Exhlbltion, N e w Orleans, Sept. 26-29.

60ugh. D. I. and Bell, 3. S.: "Stress Oricnta- t lons from 011 Y e l l Fractures I n Alberta and Texas." Calif. J. Earth %I. (1981) 18, 638.

Plumb, R. A. and Hlckman, S. H.: *Stress Induced Borehole Elongation: A Comparlson between the Four-Ann Dlpmeter and the Borehole Televiewer," accepted f o r J . Ccophys. Res. (Jan. 28, 1985).

OavIs, 9. H.: 'Surface Deformation Associrtcd u l t h a Dipping Hydrofracture,' d. Gcophys. Res.

Yood, R. D., Pollard, 0. D., and Raleigh, C. 8.: 'Determlnatlon o f I n S l tu Geanetry o f &draw l i c a l l y Generated Fractures using Tiltmeters," aper SPE 6091 presented at the 1976 SPE Annual

{echnlcrl Conference and Exhibltlon, k w Orleans,

Yood, H. D., Parkln, C. Y., e t 81.: "Fracture Proppant Mapping by Use of Surface Superconduct- ing Magnetometersr" paper SPE/DOE 11612 presented rt the 1983 DOE/SPE Symp. on Low Penneabillty, Denver, k r c h 14-16.

volght, 8.: 'Detennlnatlon o f the VIrgIn State of Stress I n the V ic ln i t y o f a Borehole from Wea- surunents o f a Par t la l Anelattlc Straln Tensor i n Or111 Cores," Fe la tch rn l k V. Ingmlcurcol (1968)

(July 10, 1983) I, NO. 87.

O c t o 3-6.

6, 201-215.

Teufel, 1. Y.: "In S i tu Stress State I n the lbunds Test Well: As Detcrmlned by the Anelastic Strain Recovery Wethod ," presented SPE/DOE 13896 presented at the 1984 SPf/DOE Symp. on Low-Peme- r b l l l t y Reservotrs, Oenver, Hay 19-22.

Teufel, 1. Y. and Yarplnskl, N. R.: "Detemina- t l o n o f I n S i tu Stress from Anelastlc Strafn Recovery kasuranents @f Orlanted Core: Canpart- son t o hydraulic Fracture Stress kasuranents I n the Rol l lns Sandstone; prE. 1984 Spp. on Rock kchanlcs, Evanston, June.

OF SEVEN FRACTURE ZVDC. m a m e u) mace. IS i s imporrant t o cnaireng 4

'

7 r - w - core rnalysls I n rG crm-ana. A t r alnlnun, severa di f ferent rnalysls procedures should be mployed .I both t o detennlne the best procedure8 and to t es t t h rs tmpt lons used In the r n a l y ~ i s .

Finally, It was not& t h a t a t least f o r t h l depth, t l l tme te rs were capable o f measuring not on1 the fracture rrlmuth, but r l s o ldent l fy lng othe aspects of r complex f racture geometry.

REFEREEES *

1. Elklns, 1. F. rnd Skov, A. H.: 'Detewlngtlon c Frrcture Orlentatlon from Pressure Interference,

2. Clnco-Ley, H. and famanlego, F.: 'Detemlnatlc o f the Orlentation o f a F l n l t e Conductlvil Vertlcal Fracture by Translent Pressure Anal) StsD" paper SPE 6750 presented a t the 1977 SI Annual Technlcal Conference and Exhlbitlor Denver, Oct. 9-12.

3. Komarl C. A., Overbey, Y. K. 3r.r and Yatts, I 3.: Predlctfon o f Fracture Orlentatlon frc Orlented Cores and Aerlal Photos. West Polsc Splder f l d d , Casper, Yyanlng," Morgantom Eneq Research Center Report No. )IERC/R1-76/1 Morgantoun, Uest Vlrglnia (March 1976).

4. Logan, 3. W. and Teufel, 1. Y.: 'The Predictlc o f Wasslve Hydraullc Fracturfng f ran Analyses c Orlented Cores," Proc. 1978 U.S. Rock Hect fymp., Reno, 340-344.

5. Teufel, 1. Y.: 'Predlctlon o f &draullc Fractur Azimuth f ran Anelastlc Straln Recovery Measure ments o f Orfented Core," Proc. 1982 U.S. Natl

6. Strlckland, F. 6. and Ren, N.-K.: 'Use o f Dlf ferent ia l Straln Curve Analysis I n Predlctlng In Si tu Stress State f o r Deep Yells." I n Rock & chrnics, A State o f the M, Proc. 1980 Rock We chrnlcs symp., Rolla.

7. Ren, N.-K. and HIdson. 0. 3.: 'Predlctlng the I n Si tu State o f Stress uslng Dl f ferent ia l Yav Velocity Analyslr," Proc. 1985 U S . Rock #c $flp., Rapid city, South Dakota.

8. Snlth, H. B., Logan. 3. H., 8nd Yood. H. 0. 'Fracture k l m u t h - A Shallow Experlment,' d Energy llrroufces Tech. (June 1980) 102.

9. Power, 0. V Schuster, C. Lo, Hay Re, ar f m b l y , 3.: o''Oetectlon o f ttydrrul IC Fractur Orlentatlon and Dlnenslons I n Cased Ye l lsD0 pap( SPf 5626 presented rt the 1975 SPE Annual Technl cr l Conference and EXhlbltfOn, Dallas, k p t . 2E O c t o 1.

10. Pearson, C.: 'The Relatlonshlp between H i m s e l m l c l t y rnd Pore Pressures during Hydraull Stlmulatlon Expcrlnrents , i n Low-Permcab11 I t Granltlc ROCkS, d. EhOphs. &So (Sept. IC 1981) 86, NO. 89, 7855-7864.

11. khuster, C. 1.: 'Dctettlon u l t h l n the k l l b o l Of k l v n i c Slgnals Created by Hydraulic Frrc tu i

frwf., AIME (1960) a9.

Rock WeCh. SYIIIP., 2380246.

3 EXPERIHENT. PART X I . COnPARISON . . IMUTH MEASUREMENTS SPE 13894

io!ier$m r ~ ' E x t h % O ? k % O ~ Oct. 1-3. nuai iechnicai n - rescn e a e

12 .

13.

14

IS.

16

17.

18.

19.

20 .

21 .

22 .

23.

._ !#E 13894 n. B. S I T H . k - K . REN. 6. 24. Ren, I.-K. and Roegiers, 3.4.: eDifferentlal

f t ra ln Curve Analysis - A New k t h o d for Deter. mining the Pnexlstlng In Sltu Stress State from Rock Con Heasurenents,' 5th Congress Int. Soc,

25. Wont Qnery, C. 1. rnd Ren, W.-K.: .Dlffepntlal US6S Uorkshop on I(ydraul1c Fracturing Stress &a. ctrment , knterey (Dec. 1981 ) .

26. '01tftnntIal Straln Cuwe Analysis and D i f . ferentia1 'Wave Velocity Analysis on WPunds Tesl l a 1,' Dowel1 Schlunberger Research and pevelop ncnt Report (Uay 1984).

27. Batchelar, A. S., Barla, Kern and Hearn, K.: 'Won, ltorlng Effects of Hydraulic Stimulation bj Wicroselmlc Event Location: A Case Study,' papei SPE 12109 presented a t the 1983 SPE Annual Tech. nlcal Conference and Exhibition, $an Frrncisco, O c t o

28. Hart, C. If., Engl, 0.e Uorrls, H. E., enc Fleming, R. P.: "Fracture Diagnostlc Results foi the W l t i w e l l Experlment's Paludal Zone Stlmulal tlon," paper SPf/OOE/6RI 12852 presented a t thc

QOCk k C h . (Uay 1983) Fllt-Fl27.

t t r i 0 n Curve Analysis -- Does I t York?, Proc,

SORRELLS AND 1. W. TEUFEL

29.

30.

31

32.

33.

1984 SPE/M)E/GRI Spp. on Unconventional 6as Recovery, Pittsburgh, Hay.

Sorrells, 6. 6.: 'High Frequency Wicrosefrmlc knl tor lng Clethods, Yydraul IC Fracture Dlagnos- tics Research, Annual &port (July 1984 - Ju ly 1985),. 6ar Research Znstltute, Chicago ( i n preparation) . Kanamori, H. end Anderson, 0. 1,: 'fheoretlca? Basfs of Sane tnplrical Relations In Seismology, (Lull. S t l ~ . Sot. k. 6, 1073-1095.

Trlfunac, U. D,: 'Tectonlc Stress and the Source Uechanlsm of the pperlal Valley, Callfornlc Earthquake of 1940, Bull. Seis. Sac. k. 62, 12834302.

kavey, R. Y.: 'Borehole Selsmic Unit," Sandit Wational Laboratories Report No. SANO:2-0373 (Ua)

Dobecky, f. 1.: %ydraul i c Fracture Orlentatfor usin9 Passive Borehole Seimics," paper SPE 1211t presented at the 1983 SPE Annual Technical Con. ference and Exhibition, $an Francisco, Oct.

1982)

I

TABLE: 1

awuRY Q AZfaLKH RESULTS

PROCEDURE 'IRE KIMUTH I

BOREHOLE LOGS Oownhol e le1 ev 1 s i on Callper Logs

TILTMETERS Tiltmeters

CORE ANALYSIS Core Straln Relaxation Laboratory Core Analysis

(DSCA and DWVA)

SEIStlIC )30NITORING Borehole Seismic Remote Selsmlc

N95E -

N95E

N86 E

N30W

N70E

,

TABU 2

sI))uRI Q lWEUfff t STRAIN RECOVERI IEMutMEHTS Q aRIEKKD W D S T O M CORE RUM THS: SKINNER FUWTION

11 nE Iof TEST ell'

g n u Win k l m u t h *a*

W p t h (4 ev (Ye) (ut) (4 -/cv #in/cY c H i n / r H a x Coring Trip 1 321 -9 148 126 4 8 0.95 *, 0.14 4 . 4 9 f 0.15 -0.53 2 0.14 N69'E 28'

324.3 214 162 112 0.72 0.18 0.39 2 0.19 0.47 ? 0.16 R81°E ?ioo

All Data H75'E 26'

Corlng Tr ip 2

329.0 142

329.6 174

A1 t Data

136

144

46

92

1.02 f 0.23 0.28 f 0.21 0.26 f 0.19 194OE 29'

0.91 0.15 0.45 0.17 0.51 2 0.13 W100'E fg0

U97'E $3'

Coring Trlps 1 and 2

All Data NB6'E t14'

The principal s t r a i n magnitudes ate the f inal magnitudes r u c h e d during recovery. The r a t i o s o f the pr lncipal strrlns and the azimuth of the naxlnum horizontal s t ra in &re the mean t one rtrndard dev18tlOn whicl occurred durlng recovery.

TABLE 3

OF DSCA A#) WA RESULTS FROn THE SKINNER FORKMIOH I N ll€ W)UWDS E S T YELL

,

Type of lest

DSCA

DSCA

DSCA

DSCA

DSCA

DWVA

DWVA

DWVA

DWVA

DWVA

OUVA

AVERAGE

321 e9

328.3

328.5

328.8

328.9

321.9

324.3

328.3

328.5

328.8

329.5

N25'Y 25"

N25'W 24'

1144% 23'

N5.Y 26'

N40'Y 920'

N30'U *so N25.Y 24'

N38.W 23'

N47'W *lo

N86'Y 230'

IY5O.Y $2'

1 U o o Y t15' 'armax: I(axiaiun horizontal principal stress.

. .

DIP - 90' VERTICAL FRACTURE

DIP - 30'

DIP - 60'

DIP - 0" HORIZONTAL FRACTURE

Figure 1. (A) Theoretical surface dltplacments for several gMnetry fractures (after Davirl8). (6) Tilt vectors fo r the hori- zontal and vertical fractures ofl(A); t i l t vectors are always drawn to point 'downhill.

-. .

.-

*

Flgure 2. (A) Actual t l l t vectors matured durlng f irst water lnjectlon lnto well; (8) mdel-generrted t l l t vectors for N95E fracture.

I

THEORETICAL 4 OBSERVED

.N

:

:

? X

2 z

Figure 3. (A t h

Raw data recorded durfng gel injection; ( B ) actual and oretical t i l t vectors for gel fnjectlon.

. . I --

.

I

I

L

FIgure 4. Structural features o f eastern Oklahm (from Pennuell wpr).

. "

MOUNDS, OKLAHOMA HYDRAULIC FRACTURE TEST SEISMIC ARRAY

. Figure 5. Array map of seismic lnttnmentation.

. ,

Figure 6. Polarization o f "single-phase" events recorded with downhole three-axis geophone package