The Impact of Fine-scale

8/12/2019 The Impact of Fine-scale

1/34

The impact of fine-scaleturbidite channelarchitecture on deep-water

reservoir performanceFaruk O. Alpak, Mark D. Barton, and Stephen J. Naruk

A B S T R A C T

T h i s a r t ic l e c o n ce n tr a t es o n t h e q u es t i on , W h ic h p a ra m et e rsg o v e r n r e c o v e r y f a c t o r ( R F ) b e h a v i o r i n c h a n n e l i z e d t u r b i d i t er e s e r v o i r s ? T h e o b j e c t i v e i s t o p r o v i d e g u i d e l i n e s f o r t h e s t a t i c

a nd d y na mi c m o de l in g o f c oa rs e r es er vo i r- sc al e m o de l s b yp r o v i d i n g a r a n k i n g o f t h e i n v e s t i g a t e d g e o l o g i c a n d r e s e r v o i re n g i n e e r i n g p a r a m e t e r s b a s e d o n t h e i r r e l a t i v e i m p a c t o n R F .O n c e h i g h- i m po r t an c e ( H ) p a ra m e te r s a r e u n d er s to o d , t h eno ne c an i n co rp or at e t he m i n to s ta ti c a nd d y na mi c m od el s b yplacing them explicitly into the geologic model. Alternatively,o n e c a n c h o o s e t o r e p r e s e n t t h e i r e f f e c t s u s i n g e f f e c t i v e p r o p -erties (e.g., pseudorelative permeabilities). More than 1700 flows i m ul a t io n s w e re p e rf o rm e d o n g e ol o g ic a l ly r e al i s ti c t h re e -dimensional sector models at outcrop-scale resolution. Water-flooding, gas injection, and depletion scenarios were simulatedfor each geologic realization. Geologic and reservoir engineer-i n g p a r a m e t e r s a r e g r o u p e d b a s e d o n t h e i r i m p a c t o n R F i n t oH, intermediate-importance (M), and low-importance (L) cat-e g o r i e s . T h e r e s u l t s s h o w t h a t , i n t u r b i d i t e c h a n n e l r e s e r v o i r s ,dynamic performance is governed by architectural parameterssuch as channel width, net-to-gross, and degree of amalgamation,and parameters that describe the distribution of shale drapes,p a r ti c ul a r ly a l o ng t h e b a s e o f c h an n e l e l e m e nt s . T h e c o n cl u -s io ns o f o ur s tu dy a re r es tr ic te d t o l ig ht o il s a nd r el at iv el y h ig h-permeability channelized turbidite reservoirs. The knowledge

d ev e lo pe d i n o ur e xt en si v e s i mu l at i on s t ud y e na bl es t he d e-v e l o pm e nt o f a g e ol o g ic a l ly c o ns i s te n t a n d e f fi c i e nt d y n am i cm o de l in g a pp r oa c h. W e b r ie f ly d es c ri b e a m e th od o lo gy f or

A U T H O R S

Faruk O. Alpak Shell International Ex-ploration and Production Inc., 3737 BellaireBoulevard, Houston, Texas;[email protected]

Faruk O. Alpak is a senior reservoir engineer inthe IUP/ICP Research and Development andSubsurface Modeling Team, Shell InternationalExploration and Production Inc. He holds a Ph.D.in petroleum engineering from The Universityof Texas at Austin. Before joining Shell, Alpakworked at the Schlumberger-Doll Research Cen-ter as a visiting scientist on mathematical mod-eling and inversion projects and at The Universityof Texas at Austin as a research assistant. Hisspecialization areas are reservoir simulation,upscaling, inverse problems, and computationalelectromagnetics.

Mark D. Barton Shell International Ex-ploration and Production Inc., 3737 BellaireBoulevard, Houston, Texas;[email protected]

Mark D. Barton is a senior geologist in the ClasticResearch Team, Shell International Explorationand Production Inc. His research interests includesedimentology and stratigraphy and their appli-cation to the characterization of hydrocarbonreservoirs. Work experience involves a variety ofprojects ranging from deep-water developmentsto oil sands mining. He worked at the Bureauof Economic Geology at The University of Texas,Austin before joining Shell in 1998.

Stephen J. Naruk Shell International Ex-ploration and Production Inc., 3737 BellaireBoulevard, Houston, Texas;[email protected]

Stephen J. Naruk has more than 20 years ofexperience with Shell, in multiple exploration,production, and research assignments. He iscurrently the principal structural geologist ofShell and leads both the Structural Geology Re-search Team of Shell and the Reservoir ModelingCenter of Expertise within the Expertise andDeployment organization of Shell.

A CKNOWLE DGE M E NTS

We thank Marc Alberts, Ru Smith, and MarkHempton for supporting this work and ShellInternational Exploration and Production Inc. for

Copyright 2013. The American Association of Petroleum Geologists. All rights reserved.

Manuscript received June 15, 2011; provisional acceptance August 16, 2011; revised manuscript received

January 22, 2012; final acceptance April 2, 2012.

DOI:10.1306/04021211067

AAPG Bulletin, v. 97, no. 2 (February 2013), pp. 251 284 251


2/34

g e ne r at i n g e f fe c ti v e p r op e rt i e s a t m u l ti p l e g e ol o g ic s c al e s , i n -c or p or at i ng t h e e ff e ct o f c ha n ne l a rc hi t ec tu re a nd r es er vo i rc o n n e c t i v i t y i n t o f a s t s i m u l a t i o n m o d e l s .

INTRODUCTION

I n r e c e n t y e a r s , o p e r a t o r s h a v e m a d e m a n y d i s c o v e r i e s i n t h eu p p e r T e r t i a r y d e e p - w a t e r p r o v i n c e s o f t h e G u l f o f M e x i c o ,N i g e r D e l t a s l o p e , a n d n o r t h w e s t B o r n e o s l o p e . D i s c o v e r y o f s i gn i fi c an t o i l a nd g a s i n d ee p- w at er d ep os it i on al s et t in gs b eg a na n e r a o f r e s e a r c h i n t o t u r b i d i t e r e s e r v o i r s t o d e v e l o p w a y s o f setting reservoir performance expectations realistically (Chapine t a l. , 2 00 2; B er g a n d K j a rn e s, 2 0 03 ) . E a r ly w e l l p e rf o r ma n cef r o m t h e s e d i s c o v e r i e s h a s , i n m a n y c a s e s , m e t a n d , i n s o m ec as es , s ur pa ss ed e x pe ct at i on s e st ab l is he d a t t he t i me o f p r oj e c t s a n c t i on ( K e nd r ic k , 2 0 00 ; H a mp t on e t a l . , 2 0 06 ) .O p er a to r s i n w e st A f ri c a r ep or te d g oo d c on ne ct iv it y b as ed o ninterference testing and early production from channelized tur-b i d i te r e se r vo i r s t h at f i l l l a r ge s u bm a ri n e v a l l ey s ( H u mp h re y se t a l ., 1 99 7 ; B o uc he t e t a l ., 2 00 4) . M any o f t hese hi gh-p e rf o r mi n g f i e ld s a n d r e se r vo i rs , h o we v er , h a ve n o t r ea c he d alevel of maturity that permits accurate estimation of their ulti-mate recovery factor (RF).

I n o th er c as es , o pe ra to rs h av e e nc ou nt er ed s ev er el y i m-p ai re d r es er vo i rs a mo ng t he se r ec en t d ev el op me nt s. T he

s ho rt fa ll s a re a tt ri bu te d i n l ar ge p ar t t o r es er v oi r c om pa rt -m en ta li z at io n. O pe ra to rs o f c ha nn el i ze d f i el ds , s uc h a s t heS c hi e ha l l io n f i e ld , w e st o f S h et l a nd s ; t h e R a m P o we l l f i e ld i nt he G ul f o f M ex ic o; a nd t he B it te rn f ie ld i n t he N or th S ea ,s us pe ct t ha t c ha nn el a rc hi t ec tu re a nd t he p re se nc e o f s ha led ra pe s h av e a s i gn i fi ca nt i n fl u en ce o n h yd r o c ar b o n r e c o v er y( G o v a n e t a l . , 2 0 0 6 ; B a r t o n e t a l . , 2 0 1 0 ) . I n d i v i d u a l c h a n n e ls t o ri e s a n d t h ei r s h al e a r ch i t ec t u re i n t ro d uc e s i g ni f i ca n t u n -c e rt ai n ty i n to s t at i c r es er vo i r m o de ls b ec a us e t h ey a r e t o o s m al lt o r e so l v e o n c o n ve n ti o n al t h re e -d i m en s i on a l ( 3- D) s ei sm ic

d at a u se d i n f i el d d ev el op me nt s. T hu s, d y n a m i c e f f e c ts o f t h es u bs u rf a ce r i sk s a n d u n ce r ta i n ti e s r e la t ed t o t h es e f e at u re sm u st b e u nd er st oo d i n a dv a nc e ( b ot h i n t e rm s o f u ps i de a ndd ow ns id e r is ks ) s o t ha t p la ns c an b e m ad e t o a cq ui re d at ad ur i ng a pp r ai s al a nd d ev e lo p me nt s u ff i ci en t t o r e du ce t he i runcertainty.

A v a s t l i t e r a t u r e e x i s t s o n c h a n n e l i z e d t u r b i d i t e r e s e r v o i r sa nd f l ow -s i mu l at i on s t ud i es c o nd uc te d f o r s u ch r e se rv o ir s.P r ov i di n g a c om p re he ns iv e l i st o f s u ch s t ud i es i s b ey o nd t h es c op e o f o ur a r ti c le . H av i ng s ta te d t ha t, w e d es cr i be b el ow a

permission to publish this paper. Ciaran OByrne,Bradford Prather, and Carlos Pirmez were in-strumental in the collection of data presentedin the study as well as in the development ofideas presented here. The authors also thankDavid G. Morse and two anonymous reviewersfor helping us enhance the quality of the

manuscript.The AAPG Editor thanks the two anonymousreviewers and David G. Morse for their work onthis paper.

E DI TORS NOTE

Color versions of Figures 1618 may be seen inthe online version of this paper.

252 Deep-Water Reservoir Performance


3/34

f ew r ef er en ce s r el ev an t t o o ur s tu dy . L ar ue a nd Y ue( 2 0 03 ) c o nd u c te d a c o m pa r at i ve r e se r vo i r d a t ab as es t ud y c on ce nt ra t in g o n d ee p- wa t er r e se rv o ir s t oevaluate the influence of stratigraphy on oil recov-ery. Larue (2004) used outcrop models to quantifyt he u nc e rt a i nt y i n t h e p r ed i ct i o n o f v o l um e s a n d

r e co v e ry i n d e ep - wa t er c h an n el i z ed s l o pe r e se r -v o ir s. L ar ue a nd F ri e dm an n ( 2 00 1, 2 00 5) a nd L a ru ea nd H o va di k ( 2 00 6) a s se s se d, t h ro ug h n ov e l s ta t ic -connectivity evaluation methods and dynamic water-flood simulations, the stratigraphic connectivity char-a c te r i st i cs o f g e ne r ic c h an n el i z ed s e ct o r m o de l sconstructed via a combination of Boolean, variogram-b a s ed g e os t a ti s t ic s , a n d m u l ti p o in t - st a t is t ic s a p -p ro ac he s. D e J a ge r e t a l . ( 20 09 ) e va l ua te d t he r e-lationship between geologic parameters and the flow

b e h a v i o r o f c h a n n e l i z e d r e s e r v o i r s w i t h t h e a i d o f a n e xp er i me nt al d es i gn a pp ro ac h. U s in g t h e e x-a mp le o f 3 -D s ha le d ra pe s a tt ac he d t o c ha nn elbodies in a deep-water depositional setting, Stright ( 2 00 6) d ev e lo pe d a m et ho d ol o gy i n w hi c h s ha l edrapes are accurately upscaled and history-matchedto production data while honoring the geologic con-cept that describes the drape geometry. Li and Caers( 20 11 ) f oc us ed s pe ci fi c al l y o n t he g eo st at i st i ca lm od el i ng o f s ha le d ra pe s a nd p er tu rb ed t he l o ca ti ono f c h a n n e l s a n d e r o s i o n a l h o l e s i n t h e s h a l e d r a p e s

w i t hi n t h e c o n te x t o f a g eo l og i ca l ly b a se d h i st or y -m a tc hi n g w o rk f lo w. R ec en t w or k a l so f o cu se d o nthe definition, derivation of controlling factors, vali-dation, and application of flow-based effective prop-erties (connectivity factors [CFs]) to the dynamicmodeling of channelized turbidite reservoirs (Alpak e t a l . , 2 0 1 0 , 2 0 1 1 ) . T h e s e n s i t i v i t y s t r u c t u r e o f t h eC F s w e re r e ve al ed v i a f l ow s i mu l a ti o n s c o n du c te do n s e c t or m o d e l s a t m u l ti p l e g e o l o gi c r e so l u ti o nsusing fine-scale parent and stepwise-coarsened off-

s pr in g m od el s i n A lp ak e t a l. ( 20 10 ). T he m ai nf o cu s o f t he w or k w as d er iv at io n o f C Fs , w hi ch w er ethen converted to pseudorelative permeability (flow-b as ed e ff ec ti ve p r o pe r ty ) f u nc t i on s t o m i m ic t h ed y na m i c e f fe c ts o f f i n e- s ca l e c h an n el i z ed t u rb i -d i t e a r c h i t e c t u r e i n r e l a t i v e l y c o a r s e r f a s t - r u n n i n gr e se r v oi r - si m u la t io n m o d e l s. S u b s eq u e n t ly , A l p a k et al. (2011) presented a novel method, which usesflow-based effective properties to retain geologic re-a li sm i n h i s to r y -m a t ch i ng w o rk f l ow s . A n a p pl i c a-

t i on o f t he m et ho d w as c on du ct ed o n a d at a s et f r oma w e s t A f r i c a n c h a n n e l i z e d t u r b i d i t e r e s e r v o i r .

T h e c o m p l e x m u l t i s c a l e s h a l e a r c h i t e c t u r e o f c h an n el i z ed t u rb i di t e d e po s i ts r e qu i r es m o de l st h a t r e s o l v e t h e f u l l a r c h i t e c t u r a l d e t a i l . O n l y t h e nc an t he a cc ur at e f lo w a nd t ra ns po rt b eh av i or o f t he

stratigraphic architecture be computed via flow sim-u l at i on s. T hi s i s w hy t h e s e ns i ti v it y s tu d ie s c on -d uc t ed f o r f l ow -b as e d e f fe c ti v e p ro pe rt i es i n A l pa k e t a l . ( 2 01 0) i n vo l ve d f i ne -s ca l e s ec to r m o de l s i m-u l a t i o n s . B e c a u s e t h e f o c u s o f t h e w o r k w a s o n t h edevelopment of effective properties, the sensitivity-s tu dy r es ul ts w er e r ep or te d b ri ef ly a nd o nl y f or t heC F s a s t h e d y na mi c m o de l in g o u tc om e . T he s e n-s i ti v it y s tr u ct u re o f t h e C F a n sw er s t h e q ue s ti o n:Which stratigraphic parameters govern the neces-

s a ry c o rr e ct i o n f o r a c o ar s e- s c al e d y n am i c m o de ls u ch t h at i t w il l a p pr o xi m at e t h e d y na mi c b e ha v io ro f a f i ne -s ca l e m o de l ? T he a ns w er i n ev i ta bl y d e-pends on the stratigraphic resolution of the coarse-s c al e m o de l . T h is q u es ti o n, h o we v er , d i ff e rs f r omWhich parameters govern RF behavior? which isp o s e d o n l y f o r f i n e - s c a l e m o d e l s . I n t h i s a r t i c l e , w ea n al y ze i n d et a il t he f i ne - sc a le s ec t or m o de l s i mu -l at io ns a nd c on du ct a s tu dy t o p ri or it iz e t he p ar a-meters that affect the RF behavior. We predominantlyleave aside the derivation of scaleappropriate flow-

b a s e d e f f e c t i v e p r o p e r t i e s c o v e r e d i n o u r p r e v i o u sp ub l ic a ti o ns . O n ly a b r ie f s um ma ry o f o ur e ff e ct i vep r op er ty a pp ro ac h h as b ee n p re s en t ed i n t hi s w or k b ec aus e i t i s a n i mpo rta nt f act or i n t he w ay w ev a l id a t e o u r s i m ul a t io n s a g ai n s t f i e ld o b s er v at i on so f r e co v er y p e rf o rm a nc e . T h e o b je c ti v e i s t o p r o-v id e g ui d el in es f or t he s ta ti c a nd d yn am ic m od el i ngo f c oa rs e r es er vo i r- sc al e m od el s b y p ro vi d in g ar a nk i ng o f t h e i n ve s ti g at e d g e ol o gi c a n d e n gi n ee ri n gp a ra m et e rs b a se d o n t h ei r r e la t i ve i m pa c t o n R F .

H e re a ft e r, w e w i l l r e fe r t o t h e g e ol o gi c a n d r e se r vo i rengineering parameters together as (uncertainty)matrix parameters for brevity. Simulations are con-d uc te d o n d et ai l ed 3 -D s ec to r m od el s c on st ru ct ed a t the outcrop-scale resolution by representing accu-rately the full-detail channel architecture up to deci-meter scale. Waterflooding, gas-injection, and gas-depletion scenarios are simulated for each geologicr e al i z at i o n . F o r s i m pl i c i ty , w e w il l h er ea ft er r ef ert o t h e g a s- d ep l e ti o n r e co v e ry m e ch a ni s m a s t h e

Alpak et al. 253


4/34

d e p l e ti o n r e c o v er y m e c h a ni s m w h e n ev e r a p p r o-p ri a te . T he e ff ec t o f s tr uc tu ra l d i sc on t in ui ti e s,

s u ch a s f a ul t s a n d f r ac t ur e s, r e ma i n s b e y o n d t h es c o p e o f t h e s e s t u d i e s .

TURBIDITE CHANNEL ARCHITECTURE

A n o v er v ie w o f t ur b id i te c ha nn el a r ch i te c tu re i sp ro vi d ed . I t r ep re se nt s t he v i ew o f t he a ut ho rs b as edo n t he a na l ys i s o f n um e ro us o ut c ro p a n d n e arsea-

floor analogs acquired from a range of depositionalsettings and locations. Our main observations are that

the (1) channel forms occur, with varying character(tributary, trunk, and distributary forms), along pro-files from submarine slopes to basin floors; (2) turbi-d i t e c h a n n e l a r c h i t e c t u r e i s c o m m o n l y m u l t i s c a l e ,d i s pl a y i ng a h i e ra r ch i c al o r ga n i za t i on o f s m al l e rchannel elements confined within the boundaries of larger channel elements; and (3) mudstone elements,which potentially represent low-permeability baf-f l es o r b ar ri e rs t o f l ow , a r e c om m on ly d i st ri b ut e da l on g t he b as e a nd m ar gi n o f t h e c ha n ne l e le m en t s.

Figure 1.Schematic diagramillustrating common scales ofchannelization observed fromoutcrop and nearsea-flooranalog data sets of turbiditechannel systems. (A) Channelstory consists of a relativelyconformable set of beds or bedsets bounded at the base by anerosion surface. Based on bedstacking patterns, two types ofchannel story elements are re-cognized: aggradational andlaterally accreting. (B) A channelstory set consists of a set ofchannel story elements boun-ded at the base by an erosionsurface. (C) A channel complexis defined as a set of channelstory sets bounded at the baseby an erosion surface. A distinctfacies association, referred to asthe bypass facies association,commonly overlies the erosivechannel base. It can occur at alllevels of channelization but isbest developed at the scale ofthe channel story set and chan-nel complex. 1 m (3.3 ft).



5/34

The multiscale stratigraphic architecture of tur-b id it e c h a nn e l s y s te m s i s s c he m at i c al l y i l l u st r at e di n F ig ur e 1. T he s ma l le st s ca l e c ha nn el - fo rm e le -m e n t i s r e f e r r e d t o a s t h e c h a n n e l s t o r y . I t i s c o m -p os ed o f a r el at i ve ly c on f or ma bl e s et o f b ed s o rb ed se ts b ou nd ed a t t he b as e b y a n e ro si on al s ur fa ce .

A c ha nn el s to ry i s t he s tr at ig ra ph ic p ro du ct o f ag e om o rp hi c c ha nn el a nd s c al ed t o t he s iz e o f t h es e d i m e n t g r a v i t y f l o w s t h a t p a s s e d t h r o u g h i t . T h et er m i s c om pa ra bl e t o t ha t u se d b y F ri en d e t a l.(1979), Bridge and Diemer (1983), and Willis (1993)to describe the architecture of ancient fluvial sand-stone bodies. Turbidite channel stories are typically 3t o 2 0 m ( 9 . 86 5 . 6 f t ) i n t h i c k n e s s a n d 5 0 t o 4 0 0 m(1641312.3 ft) in width. Larger scale channel ele-ments include channel story sets (informally referred

t o a s m ea nd er b el ts ) a nd c ha nn el c om pl ex es . Ac ha nn el s to ry s et c on si st s o f a s et o f g en et i ca l ly r e-lated channel stories and associated inner-levee de-p os it s b ou nd ed a t t he b as e b y a n e ro si on s ur fa ce .T he ir d im en si o ns t yp i ca l ly r an ge f ro m 1 5 t o 6 0 m(49.21 96 .9 f t) i n t hi ck ne ss a nd 30 0 t o 1 00 0 m(984.33 28 0. 8 f t) i n w id th . A t a n e ve n l ar ge r s ca le , ac ha nn el c om pl ex c on si st s o f a g ro up o f c ha nn el s to rysets and related inner-levee deposits bounded by anerosion surface. Although differences in terminologyexist, the hierarchical classification scheme is in es-

sence similar to that proposed by some previous au-t ho rs ( Sp ra gu e e t a l. , 2 00 2; M ay al l a nd OByrne,2 00 2; M ay al l e t a l. , 2 00 6) . B y c om pa ri so n, t he u sa geo f t h e t e r m channel story i n t h i s s t u d y i s s i m i l a r t ot he u sa ge o f channel element i n t he s ch em e p ro -posed by Sprague et al. (2002). In a similar fashion,t h e t e rm channel story set i s e qu i va l en t t o channelcomplex, a nd c ha nn el c om pl ex i s e qu iv al en t t ocomplex set .

C ha nn el s to ry s et s a nd c om pl e xe s r ep re se nt

e ro si o na l f ea tu re s t ha t a re s ig ni fi c an tl y l ar ge r i ns ca l e t ha n t he f lo ws r es po n si bl e f or t he ir f or ma ti o n.T h e y a r e a n a l o g o u s t o a v a l l e y i n t h a t t h e i r d e v e l -o p m e n t i s t h e c u m u l a t i v e p r o d u c t o f e r o s i o n b y as ma ll e r c ha nn el ( S yl v es te r e t a l ., 2 01 1) . T he d i f-f er en t s ca l es o f c ha nn el i za ti on ( ch an ne l s to r ie s,s to ry s et s, a nd c om pl ex es ) a re i nt er pr et ed t o r ec or dr ep ea te d a dj us tm en ts ( re la ti v e f al l s a nd r is es ) i n t hes lo pe e qu il ib ri um p ro fi le o f t he c ha nn el s ys te mthrough time. Downslope avulsions and subsequent

knickpoint erosion and retreat represent a mechan-i sm t ha t c ou ld c au se r ep ea te d a dj us tm en ts i n t hee qu il i br iu m p ro f il e a t m ul ti pl e s ca le s. O th er p ro -c es se s t ha t c ou ld c au se f lu ct ua ti on s i n t he s lo peequilibrium profile include tectonics associated witha mobile substrate and high variability in sediment

discharge and flow capacity (Pirmez et al., 2000).C ha nn el s to ry f il l s d is pl a y d is ti nc ti v e b ed a nd /o r

bed-set stacking patterns that range from verticallya gg ra di ng t o l at er al l y a cc re ti n g ( Fi gu re 1 A) . B ed sand/or bed sets within vertically aggrading fills dis-p la y c on ve rg en t t o o nl a pp in g r el at i on sh ip s w it hadjacent channel margins. Convergent margins arecomposed of thin-bedded successions of sandstonea nd m u ds to n e, w h er ea s o n la p m a rg i ns a re c o m-p o se d o f t h i ck - b ed d ed s u cc e ss i o ns o f a m al g a ma t ed

sandstone. Outcrop observations suggest that con-vergent margins tend to occur on the inside bend oft he c ha nn el , w he re as o nl ap m ar gi ns a re c om mo n o nthe outside channel bend. In vertically aggrading fills,channel erosion (channel deepening), sediment by-p as s ( c ha nn el w id en in g) , a nd c ha nn el f i ll i ng o cc ur i ns e pa r at e p h as e s. T u rb i di t e c h an n el f i l ls c h ar a ct e r-i z e d b y l a t e r a l l y a c c r e t i n g b e d s h a v e a l s o b e e n o b -s e r v e d f r o m o u t c r o p e x p o s u r e s ( L i e n e t a l . , 2 0 0 3 ;A r no t t, 2 0 07 ) a n d i n h i gh - re s ol u t io n s e is m ic d a taf ro m n e ars e a- f l oo r a n al o gs ( A br e u e t a l . , 2 0 03 ;

K o l l a e t a l . , 2 0 0 7 ) . T h i s t y p e o f c h a n n e l f i l l i s i n t e r -preted to record lateral channel migration related tot h e e r o si o n o f s e di m en t f r om t h e o u t si d e b en d o f t h e c ha n ne l f o ll o we d b y r ed ep os i ti o n o f s ed i me n t o n t h e i n si d e b e nd d ur i ng t h e s am e f l ow e ve nt . T h eproduct of this process is lens-shaped point-bar de-posits similar to those observed in fluvial systems.

A d is ti nc t f ac ie s a ss oc ia ti on , r ef er re d t o a s t hebypass facies association, commonly separates thechannel fill (represented by the aggradational stack

o f b e d s a n d / o r b e d s e t s ) f r o m t h e b a s a l e r o s i o n s u r -f ac e ( Be au bo ue f e t a l ., 2 00 0; G ar dn er a nd B o re r,2000). The bypass facies association is typically ane x tr e me l y h e te r ol i t hi c f a ci e s a s so c ia t io n ( c om -p o se d o f u n co m mo n ly c o ar s e- a n d f i ne - gr a in e dsediments) characterized by features suggestive ofs i g ni f i ca n t s e di m e nt r e wo r k in g a n d e r os i o n ( B a rt o ne t a l . , 2 0 0 7 b ; B a r t o n e t a l . , 2 0 1 0 ) . T h e m i x t u r e o f c o ar s e a n d f i n e m a t e r ia l s i s i n t er p re t ed t o r e pr e -s e n t s e l e c t i v e d e p o s i t i o n f r o m t h e h e a d a n d t a i l o f

Alpak et al. 255


6/34

numerous sediment gravity flows that mostly passedthrough the channel during downslope transport.

A n o u tc r op e x am p le e x hi b i ti n g m u l t i pl e s c al e so f e r o s i o n a n d f i l l i n g a r e i l l u s t r a t e d f r o m t h e P o p ochannel outcrop, west Texas (Figure 2). Other out-crop examples include the Beacon channel complex,Brushy Canyon Formation, west Texas (Pyles et al.,2010); Buena Vista channel complex, Brushy Can-yon Formation, west Texas (Rossen and Beaubouef,2007); San Clemente channel complex, CapistranoFormation, California (Chapin and Keller, 2007);c ha nn el c om pl ex es i n t he P ab R an ge , P ak i st an

( E s c h a r d e t a l . , 2 0 0 3 ) ; a n d t h e C o n d o r c h a n n e lcomplex, Cerro Toro Formation, Chile (Barton et al.,2007b).

M ud s to ne a nd h et e ro l it hi c s tr a ta c o mm on l yo v er li e t he b a se o f t he c ha nn e ls . T h es e e l em en tsa r e i n f or m al l y r e fe r re d t o a s c h a nn e l -b a s e d r ap e sa n d r e p r e s e n t a c o n f i g u r a t i o n o f s t r a t a t h a t o v e r l i et h e c h a n n e l - b a s e e r o s i o n s u r f a c e a n d t h a t m a y a c t a s a p ot en ti al b af fl e o r b ar ri er t o f lo w. T he y a rec o m m o n a t a l l s c a l e s o f c h a n n e l i z a t i o n a n d m a y b e

f o rm ed b y s ev e ra l d i ff e re nt p r oc e ss es ( B ar to n e t a l .,2 0 1 0) . ( 1 ) A b an d o nm e nt d r ap e s c o n si s t o f h e m i-

p e l a g i c m u d s t o n e s a n d f i n e - g r a i n e d s e d i m e n t s d e -r i ve d f ro m s u sp en s io n f al l ou t o r d i lu t e t u rb i di t yf l ow s t h at h a ve s p il l ed i n to t h e c ha nn el f r om a n-o t he r s o ur c e. T he y c ou l d p o te nt i al l y f or m i f t h ec h a nn e l b e ca m e t e mp o ra r i ly a b a nd o n ed a n d s u b-sequently reoccupied (Figure 3A). (2) Convergent-m a rg i n d r ap e s d e v el o p a s t h e c h a nn e l p r og r es s i ve l yf i ll s . C o ar se - gr a in ed m a te ri a l i s d ep o si t ed i n t h ea x is o f t h e c ha nn el w he re as f i ne -g r ai n ed m at e ri a l i sd e p os i t ed a l o ng t h e m a rg i n s, c o n ve r gi n g l a t er a ll y

t o f o r m a m a r g i n d r a p e . T h e d e p o s i t i s t h e d i r e c t result of density-flow height and channel-margin re-lief. Laterally, the convergent-margin drapes inter-f i ng er w i th s an ds to n e b ed s i n fi l li n g t he a xi s o f t hec h a n n e l (F i g u r e 3 B) . ( 3 ) B y p a s s d r a p e s a r e m u d d ya n d / o r h e t e r o l i t h i c d e p o s i t s l e f t b e h i n d b y t u r b i d -i t y f l o w s t h a t m o s t l y p a s s t h r o u g h t h e c h a n n e l a n dc o n ti n u e d o wn s l op e (F i g u r e 3 C) . T h e y d i f f e r f r o mc o n ve r ge n t -m a rg i n d r ap e s i n t h at t h ey a r e d e po s -i t ed b ef o re t he m a in p ha s e o f c ha n ne l f i ll i ng a nd

Figure 2.(A) Photograph panel of the Popo channel outcrop looking east. The exposure is 600-m (1970-ft) long and 80-m (262-ft) thick.The north-south orientation of the outcrop is approximately perpendicular to the primary paleoflow direction, which is to the east andsoutheast. (B) Bedding diagram of the Popo channel outcrop. The outcrop can be subdivided into a series of channel story sets (color codedon diagram) that are 25-m (82-ft) thick and 350-m (1150-ft) wide. Internally, the channel story sets are composed of three to five channelstory elements. Channel story sets 1 to 4 appear to infill a larger erosional container that displays more than 50 m (148 ft) of relief (figurefrom Barton et al., 2007a; used with permission from AAPG). The episodic nature of the downcutting phase is recorded as a series of smallerosional terraces and associated remnant channel margins along the left margin of channel story set 4 (green fill). Siltstone drapes locatedalong the base of the channel story sets are highlighted in red.



7/34

are found in close association with facies suggestiveof significant erosion and sediment reworking suchas coarse-grained lag deposits, cross-stratified sand-stones, and shale-clast conglomerates.

A n o u t c r o p p h o t o g r a p h o f a n i n t e r p r e t e d c o n -v e rg e nt - ma r gi n d ra p e l i n in g t h e b a se o f a c h an n els t o r y e l e m e n t i s s h o w n i n F i g u r e 4 A . Convergent-m ar gi n d ra pe s a re g en er al ly l e ss t ha n a m et er i nt hi ck n es s a nd c om po se d o f a b ed de d m ud st on et h a t t h i n s t o w a r d t h e a x i s o f t h e c h a n n e l . A b y p a s sd r a p e a s s o c i a t e d w i t h a c h a n n e l s t o r y s e t i s s h o w nin F i g ur e 4 B. B yp as s d ra pe s t en d t o b e r el a ti v el yt h i c k , a r e c o m p o s e d o f m a n y d i f f e r e n t f a c i e s a n de ve nt s, a nd c om m on l y t h i ck en i nt o t he a xi s o f t h e

c h an n el . B y p as s a n d c o nv e r ge n t- m ar g in d r ap e sare collectively referred to as shale drapes for sim-plicity when dynamic modeling is discussed in thetext.

F i e l d- b a se d o b s er v a ti o n s f r o m n u m er o u s t u r -b i di t e c h an n el e x po s ur e s i n di c at e t h at a b an d on -m e nt d r ap e s a r e u n co m mo n , w he r ea s c o nv e rg en t -m a r g i n a n d b y p a s s d r a p e s a r e c o m m o n l y o b s e r v e da nd m ay o cc ur i n t he s am e c ha nn el e le me nt . Am o de l s h ow i ng h o w t h e t w o e n d- m em b er d r ap et y p e s a r e p o t e n t i a l l y l i n k e d a l o n g a s l o p e e q u i l i b -r iu m p ro fi le t hr ou gh t he c ha nn el s ys te m i s s ho wn i nFigure 5. T he s lo p e e q u il i br i um p ro f il e i s a p ro x yf o r t h e d ow n sl o pe t r an s fe r o f s e di m en t b y s ed i me nt

Figure 3.Schematic illustratingthe distinct types of channel-basedrapes that have been observedfrom outcrop exposures of turbi-dite channel deposits (Barton et al.,2010). (A) Abandonment drapes(gray) form when the channelbecomes abandoned after initialincision and is subsequently re-occupied. They consist of hemi-pelagic mudstones and fine-grained sediments derived fromsuspension fallout or dilute tur-bidity flows that have spilled intothe channel from another source.(B) Convergent-margin drapes(blue) consist of deposits thatpreferentially accumulate on themargin of the channel as thechannel progressively fills. (C)Bypass drapes (blue) are de-posited from the muddy tails ofturbidity flows that pass throughthe channel before the main phaseof channel infilling. They arecommonly interstratified with fa-cies suggestive of erosion and se-diment reworking such as coarse-grained sandstones and shale-clastconglomerates.

Alpak et al. 257


8/34

gravity flows (Figure 5A). Erosional processes dom-i na te u pd ip p ar ts o f t he p ro fi le . A s t he s lo pe d e-

creases in a downstream direction, depositional pro-c es se s t ak e p re ce de nc e ( Pi rm ez e t a l. , 2 00 0) . T het y pe o f d r ap e ( e. g ., b y pa ss , m i xe d, o r c on v er ge nt m a r g i n ) t h a t d e v e l o p s d e p e n d s o n t h e d e g r e e t h a t e ac h o f t h es e t wo p r oc e ss e s a re o pe r at i ve d ur i ngt h e f o r m a t i o n o f t h e c h a n n e l ( F i g ur e 5 B) . E r o s i o na nd s ed im en t r ew or ki ng i n u pd ip p ar ts o f t hep r of i l e f a v or t h e d e ve l o pm e nt o f b y p as s d r ap e s,w h er e as p r es e rv a ti o n o f d e po s it s a s so c i at e d w i t hh i g h l y d e p o s i t i o n a l f l o w s i n d o w n d i p p a r t s o f t h e

profile favor the development of convergent-margindrapes.

A s c he m at i c d i a gr a m i l l u st r at i n g t h e f a ci e s a r -chitecture and sequential development of a channel-b a s e d r a p e a s s o c i a t e d w i t h a s t o r y s e t i s i l l u s t r a t e di n F i g u r e 6. A f a l l i n t h e e q u i l i b r i u m p r o f i l e o f t h ec ha nn el r es ul ts i n t he f lo ws e ro di ng a nd do wn -c ut ti ng i nt o u nd er ly i ng s tr at a (F i gu re 6 A). Elementsa s so ci a te d w i th t he d o wn cu t ti n g p ha s e i n cl u deoverbank or levee deposits, remnant channel mar-g i ns i s ol a te d b y b ed de d m ud st on es , a nd d eb r is -f lo w a nd s lu mp d ep os it s w it hi n t he a xi s o f t he

Figure 4. (A) Outcrop example of a channel story element bounded at the base by a thin succession of bedded mudstones. Some of themudstone beds interfinger with sandstone beds infilling the channel and are interpreted as a type of convergent-margin drape. Thechannel element is approximately 8 m (26 ft) in thickness. Note that sandstones are light colored and mudstones are dark colored in thephotograph. The photograph is from the Tres Pasos Formation, Chile (uninterpreted photograph courtesy of Stanford Project on DeepSea Depositional Systems Consortium, Stanford University). (B) Outcrop photograph showing a relatively thick succession of mudstones(see bracket) lining the base of a channel story set that is approximately 25 m (82 ft) in thickness. The basal erosion surface is highlightedby the red dashed line. The succession thickens toward the axis of the channel where the mudstones interfinger with lenticular sandstonebeds (highlighted by green dashed lines). The mudstone-dominated succession is interpreted to have formed during a prolonged phaseof sediment bypass through the channel. The upper half part of the channel fill is composed mostly of sandstone. The photograph is fromthe Isaac Formation, British Columbia, Canada.



9/34

c h a n n e l . T e r r a c e d e r o s i o n a l c u t s a r e c o m m o n a n di n di ca t e t ha t t he d ow nc ut ti n g p ro ce ss w a s e pi -s o di c . A s t h e c ha nn el a c hi e ve s a s t ab l e e qu i li b ri u mp r of i l e , d o w nc u tt i n g c e as e s a n d c h an n el w i d en i n g

e n s u e s (F i g u r e 6 B) . T h i s p h a s e m a y b e c h a r a c t e r -i z e d b y a p r o l o n g e d p e r i o d o f s e d i m e n t b y p a s sa s t he c ha nn el a ct s a s a c on du it f or t he d ow nd ipt r an s po r t o f s e di m e nt . R e su l t an t d e po s i t c o n si s t s o f a c o m pl e x a s se m bl a g e o f b e dd e d m u ds t o ne s ; l e n -ticular, cross-stratified, coarse-grained sandstones;s l u mp s ; s l i de b l o ck s ; d e br i s f l o ws ; a n d i m b ri c at e ds h al e - cl a st c o n gl o m er a te s . A r i s e i n t h e e q ui l i b ri u mp ro fi le r es ul ts i n i nf il li ng o f t he c ha nn el w it h as e r i e s o f c h a n n e l s t o r i e s (F i g ur e 6 C). Convergent-

m ar gi n d ra pe s d ev el op a lo ng t he m ar gi n o f t hec ha nn el . I t p r og r es si v el y f i ll s w it h c ha nn el s to r yelements. Channel-to-channel connectivity at thes to r y a nd s to r y- s et l e ve ls c a n o cc ur w he re ( 1 ) d r ap es

h av e n ot b ee n d ep os it ed , ( 2) p re vi ou sl y f or me dd ra pe s h av e b ee n e ro de d, o r ( 3) s an ds to ne b ed s a ndlag deposits amalgamate to form a permeable bodya t t h e b a s e o f t h e c h a n n e l .

Architectural elements associated with the ero-s i o n , b y p a s s , a n d f i l l i n g p h a s e s a r e i l l u s t r a t e d f r o ma n e x po su re o f a c ha nn el s to r y s e t a t F i sh er m ensP o i nt , R o s s F o r m a ti o n , I r el a n d ( F i g u r e 7) . P h ot o -g r ap h s i l l u st r at i n g s o m e o f t h e k e y c h ar a ct e r is t i cso f c on v er ge nt -m a rg i n a nd b yp a ss d r ap es a r e s h ow n

Figure 5.Diagram illustrating the changes in channel architecture and drape morphology along an equilibrium profile longitudinal tothe channel system. (A) Diagram showing the distribution of sediments along a longitudinal channel profile after deposition from asediment gravity flow or series of sediment gravity flows (stratigraphic product is a bed or a bed set). In a downstream direction,processes associated with erosion and sediment reworking are gradually replaced by processes associated with deposition and sediment

preservation. Fine-grained sediment (mud) settles out slowly after the turbidity flow has passed, potentially forming a thin mudstonedrape across the length of the profile (modified from Mutti et al., 2003). (B) Schematic illustrating resulting channel architecturesfollowing a series of aggrading and backstepping events. Channels in updip parts of the profile potentially develop mudstone drapesalong the base of the channel, which are related to sediment bypass, whereas channels in equivalent downdip parts of the profile developconvergent-margin drapes as the channel fills. Both styles of drapes (mixed) are seen in intermediate positions of the profile.

Alpak et al. 259


10/34

in F i g u r e s 8 and 9. C o n ve r ge n t- m a rg i n d r ap e s a r echaracterized by an angular basal discordance over-l ai n b y a m ud st on e t h at i s i n te r st ra t if i ed w it h a n

u p wa r d b e d- t hi c k en i ng s u cc e ss i on o f c h an n el -margin sandstones (F i g u r e 8 A , B). Bypass indicatorss uc h a s s h al e - cl a s t c o n gl o m er a te s a r e c o m mo n l y



11/34

Figure 7.(A) Photograph panel of Fishermens Point, Ross Formation, Ireland. The exposure is 100-m (328-ft) long and 20-m (65-ft)

thick. (B) Bedding diagram of the exposure illustrating architectural elements commonly observed at the scale of a channel story set,including (1) a remnant channel margin (green fill) formed during the downcutting phase; (2) a heterolithic assemblage (purple fill) oflenticular sandstones, mud-clast breccias, and mudstone drapes developed during a phase of sediment bypass; and (3) a series ofchannel story elements and convergent-margin drape (blue fill) deposited as the channel filled.

Figure 6. Schematic diagram illustrating the evolution and facies architecture of a channel story set. Deposits associated with the activephase are colored whereas deposits from previous phases are shaded gray. Mudstone is indicated by a blue fill, and sandstone, by

shades of green, yellow, and orange. Other elements are identified on the figure. The architecture of the channel story set can besubdivided into three phases that correspond to erosion, sediment bypass, and channel filling. (A) A fall in the equilibrium profile of thechannel initiates a phase of erosion and knickpoint retreat. Downdip of the knickpoint, slumps, slide blocks, and debris-flow deposits arepreserved in the axis of the channel. If the downcutting phase is episodic, thin-bedded inner-levee and remnant channel margins may bepreserved on the flank of the channel. (B) As a graded equilibrium profile is achieved, the channel acts as a conduit for the downslopetransport of sediment and undergoes a potentially prolonged phase of channel widening and sediment bypass. Deposits include crudelybedded coarse-grained sandstones and mud-clast conglomerates; lenses of cross-stratified sandstone; thin-bedded sandstones andmudstones with wavy-, flaser-, and lenticular-bedding types; and bedded mudstones and siltstones. (C) A rising equilibrium profile resultsin channel filling by a series of aggrading channel story elements and genetically related overbank or inner-levee deposits. Convergent-margin drapes are commonly developed on the margin of the channel story elements. Note that the diagram represents a composite offeatures observed from several outcrops. For illustration purposes, not all features are represented to scale. The approximate dimensionsof the channel story set are 20 to 25 m (6582 ft) in thickness and 300 to 500 m (9841640 ft) in width.

Alpak et al. 261


12/34



13/34

n o t p r e s e n t . I n c o n t r a s t , d r a p e s f o r m e d d u r i n g t h ebypass phase display complex architectures and area ss oc i at e d w i t h d e po s it s t h at d i s pl a y f e a tu r es s u g-g es ti ve o f e r o si o n a n d s e di m e nt r e wo r k in g . F a ci e st h a t a r e i n d i c a t i v e o f s e d i m e n t b y p a s s i n c l u d e i s o -l a t e d b e d s o f c r o s s - s t r a t i f i e d s a n d s t o n e ( F i g u r e 8 C ,

D) ; s t ar v e d r i p pl e s a n d f l a se r -l a m in a t ed s a nd s to n es(F i g u r e 8 E , F); imbricate mud-clast conglomerates(F ig ur e 9 A, B) ; a nd m u lt ip l e, c l os el y s p ac e d e ro -s i on s u rf a ce s (F ig ur e 9 C, D) . I n g en er al , t he b yp as sf ac ie s i nd ic at or s a re m os t l ik el y t o b e o bs er ve dwithin the axis of the channel. However, deepeningo f t he c ha n ne l t hr ou g h t i me c an r es ul t i n n e st edl a g d ep os i ts h i gh o n t h e c ha nn el m a rg i ns . I n di c a-t o r s o f s l o p e r e a d j u s t m e n t a n d l a t e r a l b a n k c o l -l a p s e w i t h i n t h e c h a n n e l i n c l u d e s m a l l - s c a l e ( 0 . 1

1 . 0- m [ 0 .3

3 - ft ] t h ic k ) s l um ps a nd r o ta t ed s l id eb l o ck s . T h i n d e b ri s - fl o w a n d s l u rr y - be d d e po s i tsare also common components of the drape element.In contrast to the complexity observed within theb y pa ss f a ci e s a s so c ia t io n, o v er l yi n g b e ds t ha t i n fi l lt he c ha n ne l g en e ra l ly c o ns i st o f t hi c k r e pe ti t iv es u c c e s s i o n s o f m a s s i v e - t o - g r a d e d s a n d s t o n e b e d s .

I n s u bs u rf a ce s e tt i ng s , h e te r ol i t hi c b y pa s s d e -p o s it s a r e c o m mo n l y o v e rl o ok e d a s p o t en t i al b a f-f l e s o r b a r ri e r s a f f ec t i ng c h an n el - t o- c ha n ne l c o n -nectivity for several reasons. One reason is that they

are commonly misidentified as channel-margin orc ha nn el -o v er ba nk d ep os it s a nd t he re fo re a re n ot evaluated in the correct stratigraphic context. Crite-ria to differentiate thin-bedded bypass deposits fromthin-bedded overbank deposits using borehole dataare discussed in Barton et al. (2010). Thin-beddedo v e rb a n k d e po s i t s g e n er a l l y l a c k b y p as s i n d i ca to rs

a n d a r e c o mm o nl y d o mi n at ed b y b e ds t ha t d i s-play waning-flow sequences such as well-developedBouma sequences, diffuse graded bedding, or climb-i ng r ip pl es . A s ec on d r ea so n i s t ha t t he b yp as sdeposits are commonly composed of a relatively highproportion of sandstone, as illustrated in the photo-

graphs from Figures 8 and 9, a nd t he re fo re a re n ot viewed as a potential baffle or barrier to flow. Caseswhere the sandstone beds and lag deposits amalga-m at e t o f or m a p er me ab le b od y at t he b as e o f t h ec ha nn el d ef i ni t el y e xi s t. H ow e ve r, o ur o ut c ro pf i e l d w o r k o n t h e i n t e r n a l a r c h i t e c t u r e o f s u c h d e -p os it s i nd i ca te s t ha t t he s an ds to ne b ed s a re c om -m on ly e xt re me ly l e nt i cu l ar a nd b ou nd ed b y o r i n-terstratified with mudstone beds that are relativelyc on ti nu ou s. A s a r es ul t, t he u ni t a s a w ho l e e ss en -

t ia l ly b eh av es a s a b ar ri er o r b af fl e t o f l ow . A t hi rdreason is the assumption that mudstone drapes areo nl y p re se nt o n t he m ar gi n o f t he c ha nn el e le me nt a nd n ot a l on g t he b as e. T hi s i s c om mo nl y t he c as ewith convergent-margin drapes, but outcrop stud-i es o n t he d i st ri bu t io n o f b yp as s d ra pe s i n di c at et h a t t he y c om mo nl y e xt en d a cr os s t he b as e o f t hechannel.

To assess the impact that channel-base drapescould have on channel-to-channel connectivity, thedistribution of channel-margin and bypass-related

drapes were mapped in detail from several channel-ized turbidite outcrops. The percentage of channel-base erosion surfaces overlain by convergent-marginand/or muddy-to-heterolithic bypass deposits is pro-portional to the total length of convergent-margina nd b yp as s d ra pes d iv id ed b y t he t ot al l en gt h o f channel-base erosion surfaces (Figure 10A) . W he n

Figure 8. (A) Convergent-margin drape composed of bedded siltstones overlying an erosive channel story base, Brushy Canyon

Formation, west Texas. Laterally, toward the axis of the channel, the siltstones interfinger with channel-margin sandstones. (B) Beddingdiagram of the previous photograph. (C) Interpreted bypass facies association overlying erosive channel story set base, Isaac Formation,British Columbia, Canada. Lenticular beds of cross-bedded sandstone overlying an erosive channel story set base. Beds are capped bythin but laterally extensive mudstone drapes. A thin succession of flaser- to lenticular-bedded sandstones and mudstones overlies thecross-bedded sandstones. The green dashed line near the top of the photograph marks the base of a succession of thick-beddedsandstones that compose the channel fill. (D) Closeup photograph of cross-bedded sandstone and mudstone drapes. See the dashedblue outline on Figure 8Cfor the location. (E) Closeup photograph of flaser-bedded sandstones and mudstones from the previousphotograph (Figure 8C). The width of the photograph is 50 cm (20 in.). (F) Closeup photograph of lenticular- and wavy-beddedsandstones and mudstones from the previous photograph (Figure 8C). Note the lack of waning-flow sequences. The width of thephotograph is 45 cm (18 in.). (G) Interpreted bypass facies association overlying erosive channel story set base, Skoorsteenberg For-mation, Tanqua Karoo, South Africa. (H) Bedding diagram of the previous photograph. The element consists of lenticular coarse-grainedsandstones, cross-bedded sandstones, and mud-clast conglomerates interstratified with bedded mudstones.

Alpak et al. 263


14/34

Figure 9.(A) Interpreted bypass facies association overlying erosive channel story set base, Isaac Formation, British Columbia, Canada. (B)Bedding diagram of the previous photograph. The element consists of bedded mudstones interstratified with lenses of sandstone and mud-clast breccias. Although the sandstones and mud-clast breccias have erosive bases, they commonly do not fully erode underlying beddedmudstones. (C) Interpreted bypass facies association overlying erosive channel story set base, Brushy Canyon Formation, west Texas. (D)Bedding diagram of the previous photograph. The element consists of truncated successions of thin-bedded sandstone and is bounded bythin siltstone beds. The thin-bedded sandstones are discontinuous and do not appear to provide connectivity.



15/34

Figure 10.The distribution of channel-margin and bypass drapes were mapped in detail from several channelized turbidite outcrops.Mapped outcrops are from a variety of locations and depositional settings including the Brushy Canyon Formation, west Texas; the BellCanyon Formation, west Texas; the Jackfork Group, Arkansas; the Capistrano Formation, California; the Isaac Formation, British Co-lumbia; the Ross Formation, Ireland; the Ainsa Formation, Spain; the Loma de Los Baos Formation, Spain; and the SkoorsteenbergFormation, South Africa. The channel-base drape coverage is calculated as the percentage of channel-base erosion surfaces overlain by amudstone element (bedded mudstone, muddy debris-flow deposit). It is proportional to the total length of mudstone elements (L)divided by the total length of channel-base erosion surfaces (W). (A) An example showing how the average drape coverage was cal-culated for a hypothetical outcrop composed of three channel elements. The elements are named channel 1 (Ch-1) to channel 3 (Ch-3) indescending stratigraphic order. The distribution of mudstone drapes are indicated by blue fill. Drapes are absent on the margins of Ch-1and in the axis of channel 2 (Ch-2), and continuous across Ch-3. (B) Plot of the average channel-base drape coverage for each outcropstudied. The measurements are organized by channel type (story and story set) as well as inferred depositional setting (toe of slope orbasin floor, lower slope, mid- to upper slope). CS = channel story; CSS = channel story set.

Alpak et al. 265


16/34

estimating channel-base drape coverage, note that two-dimensional measurements from outcrop expo-

sures are not biased in a positive or negative mannerfrom the coverage that exists in three dimensions.The same can be said for a series of one-dimensionalm e as u re m en t s o b t ai n e d f r o m b o re h ol e d a t a. T h ec r i te r i a t o r e co g ni z e a n d q u a nt i f y t h e d i s tr i bu t i ono f c ha nn el - ba se d ra pe s u si n g c or e a nd i m ag e l o gsa r e d i s c u s s e d i n B a r t o n e t a l . ( 2 0 1 0 ) .

A plot of the average channel-base drape coveragef or e ac h o ut cr op i s s ho wn i n F ig ur e 1 0B. Measure-m en ts a re o r ga n iz ed b y c ha nn el t y pe ( s to r y a nds to r y s e t) a s w el l a s i n fe rr ed d ep os i ti o na l s et ti n g( to e o f s lo pe o r b as in f lo or , l ow er s lo pe , m id t ou p pe r s l o pe ) . I n f er e nc e s o f s l o pe s e tt i n g w e re b a s edo n t h e t yp e o f d ep os i ts a s so ci a te d w i th t he c ha n-n el s: t oe o f s lo pe c ha nn el s w er e f la nk ed b y l ob edeposits (e.g., Willow Mountain outcrop, Bell Can-yon Formation), lower slope channels were flankedb y l ow -r e li e f c h an n el - o ve r ba n k d e po s it s ( e .g . , P o poc h an n el c o mp l ex , m i d dl e B r us h y C a ny o n F o rm a -t i o n) , a nd m id - t o u pp er s lo pe c ha nn el s w er e f la nk ed

b y s l o pe m u ds t on e s o r h i g h- r el i e f l e v ee s ( C o nd o rc h a n n e l c o m p l e x , C e r r o T o r o F o r m a t i o n ) .

Channel-base drape coverage is extremely vari-a b l e a n d c o m m o n l y e x c e e d s 6 0 % , w i t h a r a n g e e x -t en di ng f ro m l es s t ha n 5 % t o m or e t ha n 9 0% . A sexpected, channel-base drape coverage appears toincrease in depositional settings and stratigraphics i tu at i on s w h er e s e di m en t b y pa ss i s m o re p r ev a -lent. Slope settings display much higher drape cov-erage than basin-floor settings (Barton et al., 2010).Channel story sets display drape coverages that are,on average, 20% higher than channel stories. Pres-e rv at io n m ay a l so b e i mp or ta nt i n d ra pe c ov er ag eb ut i t i s m or e d if fi cu lt t o p re di ct . S ev er al s lo pes et ti ng s, s uc h a s t he W in de rm er e ( Br it is h C o-l u m b i a , C a n a d a ) a n d C e r r o T o r o ( s o u t h e r n C h i l e )outcrops, exhibit significantly high drape coveragea t t h e c h a n n e l s t o r y s e t l e v e l b u t l o w d r a p e c o v e r -a g e a t t he c ha nn el s to r y l e ve l. C h an ne l s to r y d r ap esa pp ea r t o h av e b ee n f o rm e d b u t w er e s ub s eq u en tl ye r o de d a n d r e pl a c ed b y t h i ck s h al e - cl a s t b r ec c i as( B a r t o n e t a l . , 2 0 1 0 ) .

Figure 11.Diagram illustrating stratigraphic elements within the sector models. A surface-based modeling program (Wen et al., 1998;

Wen, 2005) was used to construct the sector models. Models are hierarchical in scale and are composed of channel story sets andchannel stories. (A) Channel complex composed of multiple channel story sets. In the figure, channel story sets are colored red, orange,and yellow in ascending stratigraphic order. The channel-base drape for the last channel story set is shown in purple. The regions wherethe drapes are absent are indicated by white areas. No bias of drapes toward axis or margin exists. (B) Channel story sets composed ofmultiple channel stories. In the figure, channel story sets are colored red, orange, yellow, and green in ascending stratigraphic order. Thechannel-base drape for the last channel story is shown in blue; the gaps in the drape are indicated by white areas. A weak bias in themodel exists for drapes to be placed toward the margins of the channel story.



17/34

SECTOR MODEL

High-resolution sector models are constructed usinga s ur fa ce m od el i ng p ro gr am ( We n e t a l. , 1 99 8; W en ,2 00 5) . L ay e rs w it h a s ur fa ce m od el a re g e ne r at e d b ym i g ra t i ng a s u rf a ce t h ro u gh a s e ri e s o f t i m e s t e ps .

T h e m i g ra t io n o f t h e s u rf a ce m i mi c s p r oc e ss e s a s -sociated with erosion and deposition. Surface mod-e l s h a v e s o me a d v an t ag e ou s a t t ri b ut e s. T h ey c a nc o ns tr u ct m o de ls a t t h e b ed s c al e, c re at e s t ra t i-g r ap hi c al l y r e al i st i c l ay e ri n g ( l ay er s o r e l em e nt s a reo r g a n i z e d f r o m o l d e s t t o y o u n g e s t ) , a n d r e p r e s e n t h i e ra r c hi c a l r e la t i on s h ip s . B e c au s e m a ny t y p es o f s h al e s o r m ud st on es o cc ur a t t he i n te rf a ce b et we e nb e d s o r s t ra t i gr a ph i c e l em e nt s , s u rf a c e m o d el i n ga l l o ws f o r a m o re r e al i s ti c r e pr e se n ta t i on o f s t ra t i -

graphic heterogeneity.An ex am pl e o f a s ec to r mo de l us ed i n t hi s s tu dyi s s ho wn i n F ig ur e 1 1. T he l ar ge st s ca le e le me nt s a rechannel story sets (Figure 11A). Elements that mayimpact connectivity at this scale (i.e., between chan-nel story sets) are mudstone drapes deposited alongt h e b a s e a n d m a r g i n s o f t h e c h a n n e l s t o r y s e t a n dt h e d e g r e e o f a m a l ga m a ti o n b e t w ee n i n d i v i du a lchannel story sets. Internal to the channel story setsa re c ha nn el s to ri e s (Figure 11B). Elements that mayi m pa ct c on ne ct iv i ty a t t hi s s ca le a re c ha nn el -b as e

d r ap e s, m u ds t o ne - fi l l e d c h an n el s , a n d t h e d e gr e eof amalgamation between individual stories. Withinthe channel story elements, the frequency and lateralextent of intrachannel shales were varied.

DEFINITIONS, RANGES, AND SIMULATIONLEVELS FORMATRIXPARAMETERS

Reservoir engineering parameters resemble offshore

w es t A fr ic an d at a s et s. I n t er ms o f f lu id s, t he f oc us i son relatively light oils and gas. Three fundamentallydifferent recovery mechanisms are considered forsector model simulations: (1) waterflooding in thea bs e nc e o f m o va bl e g a s, ( 2 ) i m mi s ci b le g a s i n je c-t io n i n t he a bs en ce o f m ob il e w at er , a nd ( 3) p ri -m a r y d e p l e t i o n o f g a s .

A q u i f e r a n d g a s c a p e n e r g y a r e a s s u m e d t o b en e gl i g i bl e w i t hi n t h e s e ct o r m o de l . H e re a f te r , w ew i l l r e f er t o t h e i m m is c i bl e g a s- i n j ec t i on r e co v e ry

m e ch an i sm s i mp l y a s t he g as - in j ec t io n r ec o ve rymechanism.

The primary depletion scenario for a large spec-trum of liquid hydrocarbons involves the decrease of the reservoir pressure below the bubble point in theabsence of external pressure support. The resulting

evolution of gas from liquid hydrocarbons can po-t e nt i a ll y c a us e s i g ni f i ca n t c o m pl i c at i o ns f o r a n a -l y z i n g t h e s e n s i t i v i t y s t r u c t u r e . O f c o u r s e , o n e c a nc l a i m t h a t , b e f o r e r e s e r v o i r p r e s s u r e d e c r e a s e s b e -l o w b u bb l e -p o i nt p r es s ur e , i n g e ne r al , a p r es s ur e -m a i n t e n a n c e a c t i v i t y s u c h a s w a t e r f l o o d i n g o r g a si n je ct i on i s i n it i at ed . H ow e ve r , o u r g oa l h er e i s n ot t o d er i ve R Fs f o r a p ar t ic u la r r ec ov e ry o pt i mi za ti o ns c en ar i o. I n st e ad , o u r o b je ct iv e i s t o q ua nt i fy t h eh yd r oc a rb on t ra pp i ng i n t he r es er v oi r c a us ed b y

t h e e x i s t e n c e o f f i n e - s c a l e g e o l o g i c f e a t u r e s . T h u s ,we choose to investigate the primary depletion sce-n a r i o b y a s s u m i n g a d r y - g a s r e s e r v o i r a n d f o c u s o nt h e R F b eh av i or ( as a n i n di ca to r o f h yd ro ca rb ontrapping and reservoir connectivity), with the pur-p o s e o f u n d e r s t a n d i n g t h e f i r s t - o r d e r p h y s i c s .

A comprehensive list of matrix parameters sub-ject to investigation is shown in Tables 1 and 2. T h ematrix p a r a me t er s a r e a b b re v i at e d f o r p r ac t i ca l i tyi n d o cu me n ta t io n a nd d at a m a na ge me nt . H e re -a ft er , i n t he t ex t, w e w il l a dh er e t o t he n am in g

c on ve nt i on o f T ab le s 1 and 2. We a ls o r epo rt w he th er a g iv e n p a ra me te r i s d i sc re te o r c on t in uo u sb y d ef in it io n ( ch ar ac te ri st ic 1 ) a s w el l a s w he th er ag iv e n p ar a me te r i s q ua l it at i ve o r q ua nt i ta ti v e b yn a t ur e ( c ha r a ct e ri s ti c 2 ) i n T ab l es 1 and 2. Theu n i t s o f t h ematrix p a r a m e t e r s a r e g i v e n i n t h e l a s t c ol u mn o f t he t ab l e. T a bl e s 3 and 4 document in-v e st i ga te d l e ve l s f o r t he matrix parameters. Thesep ar a me te rs a re s e ns i ti z ed s ep ar at el y f o r e ac h r e-c o v er y m e ch a ni s m . B a se - ca s e p a r am e te r s e tt i n gs

a re d is pl ay ed i n t he V 0 c ol um n. L ev el s o f v ar ia ti ona r e l i st ed u n de r t h e f o ll o wi ng c o lu mn t i tl e s: V 3,V2, V1 , V 1 , V 2 , V 3 , , a n d s o o n . U p p e r a n dl o w er b o u nd s o f v a r ia t i on d e f in e t h e i n v es t ig a te dp h y s i c a l r a n g e f o r e a c h p a r a m e t e r . W e e m p h a s i z et h at s o me o f t h e r e se r vo i r e n gi n ee r in g p a ra m et e rsrepresent combined outcomes of several subparam-eters. The parameter description column in Table 4elaborates on such relationships. Additionally, im-p o rt a n t c h a ra c te r is t i c f e a tu r es o f s e ct o r m o de l s t h at

Alpak et al. 267


18/34

r e ma i n u n ch a ng e d a c ro s s s e ns i t iv i t y s t ud i e s e x i st .S u c h f e a t u r e s a r e l i s t e d i n T a b l e 5.

WELL CONFIGURATION

T he p ri n ci p al d i re ct i on o f f l ui d d i sp l ac em e nt i sa s s u m e d t o o c c u r p a r a l l e l t o t h e c h a n n e l a x e s (Xd i re c ti o n) f o r w a te r fl o od i ng a n d g a s i n je c ti o n. Asingle injector-producerp a i r w e l l c o n f i g u r a t i o n i sc o n si d e re d f o r t h e s e n si t i v i ty - s tu d y s i m ul a t i on s .Wells are placed in close proximity to opposing

b o un d in g e d ge s o f t h e s e c t or m o de l t h at a r e p e r -p e nd i cu l ar t o t h e c h an n el a x es . W e ll s a r e p l ac e dp r ef e re nt i al l y i n ( l oc a l) h i gh n e t- t o- g ro s s z o ne s

c o n si s t e nt w i t h f i e l d d e v el o p me n t p r a ct i c es . O n ep ro du ct io n w el l i s p la ce d i n t he v ic in it y o f t hem o d e l c e n t e r f o r d e p l e t i o n s i m u l a t i o n s . O n l y v e r -t i ca l a nd f u ll y p e ne tr a ti n g w el l s a r e c o ns i de re d i nthis study.

F i g ur e 1 2 A d i sp l ay s a r ea l iz a ti o n f o r t h e w a -t e r fl o o d i ng r e c ov e r y m e c ha n i s m. S u p er i m po s e dw e l l l o c a t i o n s a r e s h o w n o n s a t u r a t i o n a n d n e t - t o -g r o ss m a p s. F i g ur e 1 2 B i l l u st r a te s a n a l og o u s p a -n e l s f o r t h e d e p l e t i o n r e c o v e r y m e c h a n i s m .

Table 1.Description of the Geologic Parameters

Parameter

Number

MatrixGeologic

Parameter Parameter Description Characteristic 1 Characteristic 2 Unit

1 BNO Number of meander belts Discrete Quantitative Dimensionless

2 BNG Meander-belt channel-to-nonchannel

ratio (meander-belt net-to-gross)

Continuous Quantitative Dimensionless

3 BNS Meander-belt channel-to-nonchannelratio shift parameter

Continuous Quantitative Dimensionless

4 BSC Meander-belt shale drape coverage Continuous Quantitative Percent (%)

5 BRS Random sequence number for the

meander-belt shale drape realization

Discrete Quantitative Dimensionless

6 BSG Meander-belt shale drape geometry Discrete Qualitative Dimensionless

7 BSH Meander-belt shale drape hole size Continuous Quantitative Element width

8 BDA Meander-belt degree of amalgamation Discrete Qualitative Dimensionless

9 CDT Channel depth Continuous Quantitative Meter (m)

10 CWD Channel widthtodepth ratio Continuous Quantitative Dimensionless

11 CSN Channel sinuosity Continuous Quantitative Dimensionless

12 CCN Channel-continuity number(frequency of mud plugs internal

to the channel)

Discrete Quantitative Number of plugsper kilometer

13 CSC Channel shale drape coverage Continuous Quantitative Percent (%)

14 CRS Random sequence number for the

channel shale drape realization


15 CSG Channel shale drape geometry Discrete Qualitative Dimensionless

16 CSH Channel shale drape hole size Continuous Quantitative Element width

17 CDA Channel degree of amalgamation Discrete Qualitative Dimensionless

18 FAR Channel-infill architecture Discrete Qualitative Dimensionless

19 FSF Channel-infill shale frequency

(thin-bedded channel margins)


20 FSC Channel-infill shale drape coverage Continuous Quantitative Percent (%)

21 FRS Random sequence number for the

channel-infill shale drape realization


22 FSG Channel-infill shale drape geometry Discrete Qualitative Dimensionless

23 FSH Channel-infill shale drape hole size Continuous Quantitative Element width



19/34

CHARACTERISTICS OF THE BASE CASE

A 3 -k m ( 9 84 2. 5 -f t) (X) b y 2 -k m ( 65 61 .7 -f t) (Y) boxw it h a t ot al th ick ne ss o f 5 0 m ( 16 4 f t) h ous es at yp ic al s ec to r m od el . H er ea ft er , i n t he t ex t, ( 1)

c ha nn el s to ry s et s a re a ls o i n fo rm al l y r ef er re d t o a sm ea nd er b el ts a nd ( 2) c ha nn el s to ri es a re a l so r e-f er re d t o a s c ha nn el s f or s im pl i ci t y. T he b as e- ca sesector model contains three meander belts exhibit-i ng a m ed iu m d eg re e o f a ma lg am at io n. O ve ra ll ,

Table 2.Description of the Reservoir Engineering Parameters

Parameter

Number

MatrixReservoir

Engineering Parameter Parameter Description* Characteristic 1 Characteristic 2 Unit

1 BXL Well-spacing parameter (fx) Discrete Quantitative Dimensionless

Well-spacing parameter (lx) Discrete Quantitative Dimensionless

Well-spacing parameter (fy) Discrete Quantitative Dimensionless

Well-spacing parameter (ly) Discrete Quantitative Dimensionless2 dipX Dip angle inXdirection Continuous Quantitative Degree ()

3 dipY Dip angle inYdirection Continuous Quantitative Degree ()

4 CR Rock compressibility Continuous Quantitative One over pound per

square inch (psi1)

5 Pref. Reference pressure (Pref.) Continuous Quantitative Pounds per square

inch (psi)

Reference depth (Href.) Continuous Quantitative Meter (m)

Initial reservoir pressure at the

reference depth (Pini)

Continuous Quantitative Pounds per square

inch (psi)

6 APIvalue PVT parameter: Hydrocarbon

fluid density (APIvalue)

Continuous Quantitative Degree API (API)

PVT parameter: average oil

density (densO)

Continuous Quantitative Pounds per cubic

foot (lb/ft3)

PVT parameter: average

water density (densW)

Continuous Quantitative Pounds per cubic

foot (lb/ft3)

7 acidNb SCAL parameter: acid number Continuous Quantitative Dimensionless

8 asph SCAL parameter: asphaltene

percentage

Continuous Quantitative Percent (%)

9 sal SCAL parameter: water salinity Continuous Quantitative Parts per million

(ppm)

10 sgc SCAL parameter: critical gas

saturation

Continuous Quantitative Fraction

11 sorg SCAL parameter: residual oil

saturation to gas

Continuous Quantitative Fraction

12 permX Horizontal permeability

(of sands)

Continuous Quantitative Millidarcy (md)

13 kvTokh Permeability anisotropy Continuous Quantitative Dimensionless

14 prRat Production rate Continuous Quantitative Reservoir barrels

per day (rbbl/day)

Injection rate (inRat = 1.2

prRat)

Continuous Quantitative Reservoir barrels

per day (rbbl/day)

15 BVS Model size in the vertical

direction

Continuous Quantitative Meter (m)

*PVT = pressure-volume-temperature; SCAL = special core analysis. The SCAL parameters determine the correlation-based relative permeability and capillary pressure

relationships.

Alpak et al. 269


20/34

Table 3.Levels of Variation for the Geologic Parameters*

Parameter

Number Parameter Parameter Description Unit V 3 V2 V1 V0 (Base C

1 BNO Number of meander belts Dimensionless 0 3

2 BNG Meander-belt channel-to-nonchannel

ratio (meander-belt net-to-gross)

Dimensionless 25 35 50 65

3 BNS Meander-belt channel-to-nonchannel

ratio shift parameter

Dimensionless No variati

(65-65-64 BSC Meander-belt shale drape coverage Percent 0 30 45 60

5 BRS Random sequence number for the

meander-belt shale drape realization

Dimensionless 1

6 BSG Meander-belt shale drape geometry Dimensionless Random

7 BSH Meander-belt shale drape hole size Element width 0.2 0.6

8 BDA Meander-belt degree of amalgamation Dimensionless Low Medium

9 CDT Channel depth Meter (m) 6 12

10 CWD Channel widthtodepth ratio Dimensionless 10 20

11 CSN Channel sinuosity Dimensionless 1.2 1.5

12 CCN Channel-continuity number

(frequency of mud plugs internalto the channel)

Number of plugs

per kilometer

0

13 CSC Channel shale drape coverage Percent 0 30 45 60

14 CRS Random sequence number for the

channel shale drape realization

Dimensionless 1

15 CSG Channel shale drape geometry Dimensionless Random

16 CSH Channel shale drape hole size Element width 0.2 0.6

17 CDA Channel degree of amalgamation Dimensionless Low

18 FAR Channel-infill architecture Dimensionless Layered Converge

19 FSF Channel-infill shale frequency

(thin-bedded channel margins)

Dimensionless 0 5

20 FSC Channel-infill shale drape coverage Percent 0 30 45 60 21 FRS Random sequence number for the

channel-infill shale drape realization

Dimensionless 1

22 FSG Channel-infill shale drape geometry Dimensionless Margin

23 FSH Channel-infill shale drape hole size Element width 0.2 0.6

*The unit element width is the average meander-belt width for erosional holes in meander-belt drapes. However, the unit element width is the average channel width for erosio

shape is assumed for the erosional holes in shale drapes in this study. Thus, the hole diameter is equal to the hole size (width) by definition. Base-case parameter settings a

listed under the following column titles: V3, V2, V1, V1, V2, V3, , and so on.

270

Deep-WaterReservoirPerformance


21/34

Table 4.Levels of Variation for the Reservoir Engineering Parameters*

Parameter

Number Parameter Parameter Description** Unit V 2 V1 V0 (Base Case)

1 BXL Well-spacing parameter (fx) Dimensionless 1

Well-spacing parameter (lx) Dimensionless 100

Well-spacing parameter (fy) Dimensionless 1Well-spacing parameter (ly) Dimensionless 100

2 dipX Dip angle inXdirection Degree 0 5 10

3 dipY Dip angle inYdirection Degree 0

4 CR Rock compressibility One over pound per

square inch (psi1)

1 105 2 105

5 Pref. Reference pressure (Pref.) Pounds per square

inch (psi)

3000 4500

Reference depth (Href) Meter (m) 2000 3000

Initial reservoir pressure at the reference

depth (Pini)

Pounds per square

inch (psi)

3000 4500

6 APIvalue PVT parameter: hydrocarbon fluiddensity (APIvalue) Degree API (API) 20 30

PVT parameter: average oil density

(densO)

Pounds per cubic

foot (lb/ft3)

f(P, APIvalue)

PVT parameter: average water density

(densW)

Pounds per cubic

foot (lb/ft3)

Reference value =

67.77; f(p)

7 acidNb SCAL parameter: acid number Dimensionless 0.7 1.0

8 asph SCAL parameter: asphaltene percentage Percent 0.465 0.7 0.727

9 sal SCAL parameter: water salinity Parts per million (ppm) 40,000 120,000

10 sgc SCAL parameter: critical gas saturation Fraction 0.02 0.05

11 sorg SCAL parameter: residual oil saturation

to gas

Fraction 0.05 0.1

12 permX Horizontal permeability (of sands) Millidarcy (md) 250 1000

13 kvTokh Permeability anisotropy Dimensionless 0.001 0.100 1.000

14 prRat Production rate Reservoir barrels

per day (rbbl/day)

5000 10,000 15,000

Injection rate (inRat = 1.2 prRat) Reservoir barrels

per day (rbbl/day)

6000 12,000 18,000

15 BVS Model size in the vertical direction Meter (m) 50

*Base-case parameter settings are displayed in the V0 column. The levels of variation are listed under the following column titles: V3, V2, V1, V1, V2, V3, , and so o

**PVT = pressure-volume-temperature; SCAL = special core analysis. The SCAL parameters determine the correlation-based relative permeability and capillary pressure rel

Alpak

et

al.

271


22/34

meander-belt net-to-gross is assumed as 65%, withchannels exhibiting a low degree of amalgamation(Figure 13A). Meander-belt, channel, and channel-i nf i ll d ra pe s a re a t 6 0% c ov er ag e l ev el a s s ho wn i nF i g u r e 1 3 A , B , a n d C , respectively. Meander-belt a nd c ha nn el d ra pe s a re d is tr ib ut ed r an do ml y ,

whereas channel-infill drapes are concentrated alongthe margins of the channels. Each channel containsfive channel-infill drapes. Commonly observed (in

Table 5.Common Characteristics of the Sector Models that Remain Unchanged over the Course of Simulations

Parameter Number Parameter Parameter Description Unit V0 (Base Case)

1 Model size Xdirection total size Kilometer (km) 3

Ydirection total size Kilometer (km) 2

Xdirection grid-block size Meter (m) 30

Ydirection grid-block size Meter (m) 20

Zdirection grid-block size Meter (m) Variable2 Wells Rate constrained Yes

Well geometry, producer Vertical

Well geometry, injector Vertical

3 flowDir Displacement (or flow) direction Dimensionless X

4 Porosity Sand porosity Fraction 0.25

Figure 12. Geology and (recovery mechanism driven) well-placement strategy used in flow simulations. Two example sim-ulation snapshots are shown: one for waterflooding and the

other for primary gas depletion. The former snapshot is takensubsequent to water breakthrough in the producer well. Thelatter snapshot is taken right after the initialization of the dy-namic model but before the producer well is opened for pro-duction. Color scheme: ([A] oil saturation [So], upper panel)So=0.093, dark blue; So = 0.91, red; ([A] net-to-gross [NTG], lowerpanel) NTG = 0.22, orange; NTG = 1.0, red; ([B] mass of gas inthe model [mg; pore volume gas density], upper panel) low mg,dark blue; highmg, green; ([B] NTG, lower panel) NTG = 0.22,orange; NTG = 1.0, red. In the above figure panels, the text boxespoint to the exact locations of the injector (INJ) well and theproducer (PRD) well.

Figure 13. (A) Base-case sector model with three meanderbelts. Horizontal slices taken from this model by peeling off thestratigraphic surfaces (and the layers between these surfaces)are used to illustrate the drape layers and the erosional holes inthese layers. (B) Plan view of the first meander-belt base layer(from the top of the model) illustrating the geometry of an examplemeander-belt drape (light green) with 60% coverage (BSC =

meander-belt shale drape coverage), including randomly distributederosional holes (dark green). (C) Plan view of the first channel-baselayer (from the top of the model within the first meander belt) il-lustrating the geometry of an example channel drape (light blue)with 60% coverage (CSC = channel shale drape coverage) andrandomly distributed erosional holes (darker blue patches in thechannel track). (D) Plan view of the first channel-infill layer (fromthe top of the model within the first channel story, which is in turnwithin the first meander belt) illus trating the geometry of anexample channel-infill drape (orange) with 60% coverage (FSC =channel-infill shale drape coverage), including erosional holes(red) distributed preferentially near the axis of the channel bed.



23/34

outcrops) convergent channel-infill architecture isa da pt ed i n t he b as e c as e. T he e nt ir e d et ai l o f t heshale architecture is modeled explicitly.

T h e m o d e l i s i n i t i a l l y s a t u r a t e d w i t h a 3 0 A P Io i l a t i r r ed u ci b l e w a t er s a tu r at i o n f o r w a te r f lo o d in ga n d g a s- i n j ec t i on r e co v e ry m e ch a ni s m s a n d w i t h

d r y g a s f o r t h e d e p l e t i o n r e c o v e r y m e c h a n i s m . A ni n it i al r es er vo ir p re ss ur e o f 4 50 0 p si ( 31 M Pa ) i st a ke n a s t h e r e fe re nc e p re ss ur e f o r p r es su r e, v o l-u m e, a n d t em pe ra tu re ( PV T) c al cu la ti o ns . O nl y t hei so the rm a l f l ow o f i n -s i tu a n d i n j ec t ed f l ui d s i sinvesti gated. A conventional black-oil formulationwith standard correlation-based PVT relationshipsi s u s e d t o d e s c r i b e r e s e r v o i r f l u i d s a s a f u n c t i o n o f ( v a ry i n g) r e se r v oi r p r es s ur e d u ri n g s i m ul a t io n . Ahomogeneous and isotropic sandstone permeability

of 1000 md and a homogeneous sandstone porosityo f 0 .2 5 a re c on si de re d i n t he b as e c as e t o m or ec l e a r l y d i s t i n g u i s h b e t w e e n t h e e f f e c t s o f s h a l e a r -c h i te c tu r e a n d p e tr o ph y s ic a l p r o pe r ti e s . S h a le s o f a l l t y pe s a re a s su m ed i m pe rv i ou s. B ei n g s uc h, t he ym a y p o t e n t i a l l y f o r m p r e v a l e n t b a r r i e r s t o f l o w i nt h e r e s e r v o i r d e p e n d i n g o n t h e a r c h i t e c t u r a l c h a r -a c t e r i s t i c s o f a s p e c i f i c g e o l o g i c r e a l i z a t i o n . A t o t a ll i q u i d ( o r g a s ) p r o d u c t i o n r a t e o f 1 5 , 0 0 0 r e s e r v o i rbarrels per day (rbbl/day) (2385 reservoir m3 p er d ay[rm3/day]) is used as the production rate constraint.

I n j e c t i o n r a t e c o n s t r a i n t i s s e t a t 1 8 , 0 0 0 r b b l / d a yo f w a t e r ( 2 8 6 2 r m3 /day) (or equiv alen t gas) ford i s pl a c em e n t- b a se d r e co v e ry m e ch a n is m s . A ninjectiontop r od u ct i on r at e r at i o o f 1 . 2 i s m a in -t a i n e d c o n s i s t e n t l y e v e n w h e n t h e p r o d u c t i o n r a t ei s v a ri ed i n t he s en si ti v it y s tu dy . I n a dd i ti o n t o r at ec o n s t r a i n t s , w e l l s a r e a l s o c o n s t r a i n e d w i t h r e a l i s -t i c m a x i m u m a n d m i n i m u m b o t t o m h o l e p r e s s u r eb o un d s. L o ng p er i o ds o f r e co v er y a l lo w r e as o n-a b l y a c c u r a t e e s t i m a t i o n o f t h e u l t i m a t e u n s w e p t

h y dr oc a rb o ns c a us ed s o le ly b y t h e e f fe c ts o f s t ra -t i g r a p h y . A l l s i m u l a t i o n s a r e r u n f o r 5 0 y r . D e p l e -t i o n s i m ul a ti o n s t y p ic a l ly t e rm i n at e e a rl i e r b e c au s eo f t h e m i n i mu m b o t to m ho l e p r es s ur e c o n st r ai n t i m po s ed o n t h e p r od u ct i on w e ll . T h e i n je c ti o nw el l i s p la ce d d ow nd ip a nd t he p ro du ct io n w el l i sp l a c e d u p d i p i n t h e r e s e r v o i r f o r t h e w a t e r f l o o d -i n g r ec ov er y m e ch a ni s m i n a l l s i mu l at i on s t h at i n vo l ve a d i pp in g s ec to r m od el . T he w el l -p l ac em en t

c o n fi g ur a t io n i s r e v er s ed f o r t h e s i m ul a ti o n s p e r-f o r m e d f o r t h e g a s - i n j e c t i o n r e c o v e r y m e c h a n i s m .

I n t he s en si t iv i ty s tu di es , t he e ff ec t o f t he s pa ti alrandomness is only evaluated for the placement oferosional holes in the shale drapes. Three realizationso f t he b as e c as e a re g en er at ed f or e ac h d ra pe t yp e.

T he p ar am et er s B RS , C RS , a nd F RS r ep re se nt t heerosional holeplacement randomness for meander-belt, channel, and channel-infill drapes, respectively.T he e ff ec t o f t he v a ri a bi l it y i n t he s pa ti al l oc at i on s o f other reservoir elements between wells (e.g., chan-nel stories) on RF has been investigated via simula-t io ns o f a v er y l im it ed n um be r o f a dd it io na l g eo -m o de l r e al i z at i o ns . I n t h es e r e al i z a ti o n s, c h an n els t or y l o ca ti o ns a r e d i f fe r en t t h an t ho s e i n t h e m o de l su se d f o r t he s en si t iv i ty s tu dy , w he r ea s a l l o t he r

c ha r ac te ri s ti c s o f t he s ec t or m od el s r em ai n u n-c h an g ed . C l e ar l y , t h e e r os i o na l - ho l e p l a ce m en t v a r i e s s i m u l t a n e o u s l y w i t h c h a n n e l s t o r y l o c a t i o n si n t h e s e o n e - o f f r e a l i z a t i o n s . W e o b s e r v e d t h a t t h ec ha nn el - st or y r an d om ne ss e f fe ct s o n R F a r e, i ng en er al , q ui t e c o mp ar ab l e t o t h os e o b ta i ne d f o r t h eerosional holeplacement randomness. This obser-v a ti o n s te ms f ro m a n o ne x te ns i ve s tu d y. A d i ff er en t c o m bi n at i o n o f c h an n el s t or y a n d e r o si o n al - h ol ep l ac em e nt n ot c a pt u re d i n o ur l i mi te d s tu d y m a yy i e l d a d i f f e r e n t r e s u l t .

RESULTS OF SENSITIVITY STUDIES

A d i me ns io n le ss n or m al i ze d i m pa ct v a lu e, N I, i sdefined to establish a quantitative sensitivity struc-ture among sensitizedmatrix parameters. The def-i n i t i o n o f N I i s g i v e n b y

NIi j maxRFi minRFi j

RFbase; i

where i 1;. . .; n: 1

In the above equation, RF denotes the vector of RFsobtained from the sensitivity simulations conductedf o r t h e v a ri a ti o n o f a s i ng l e p a ra m et e r;RFbase, t h ebase-case RF for a given sensitivity study; andn, t h en u mb e r o f p a ra m et e rs i n v es t ig a te d w i t hi n a g i v en

Alpak et al. 273


24/34

sensitivity study. Example RF, water-cut, and gas-oilr a ti o p r of i l es f o r w a te r fl o o di n g - a n d g a s i n j ec t io nbased hydrocarbon recovery mechanisms are respec-t iv el y s ho wn i n F ig ur es 1 4 and 15 a s a f un ct io n o f t hechannel shale drape coverage (CSC) parameter. TheCSC parameter significantly affects the recovery pro-f i l e b e yo n d a p pr o xi m at e ly 6 0 % c o v er a ge l e ve l f o rwaterflooding and 75% coverage level for gas injection.

T he r an ki ng o f t he matrix parameters in terms of t he ir i nf lu en ce o n R F f ol lo ws f ro m t he ir N I v al ue s( Fi gu re s 1 618) . W e e mp ha si ze t ha t s en si ti vi tycharts are not Tornado charts. For the variation of a

given parameter, a sensitivity chart does not reflect adownside or upside variation of outcomes with re-spect to a base case. Instead, it displays a normalizedr an ge o f o ut co me s i n r es po ns e t o t he v ar ia ti on s o f t he

matrixparameter under investigation. The process isr e pe a te d f o r e a chmatrix parameter subject to thesensitivity study. The magnitude of the normalizedrange serves as the criterion for determining the re-l at iv e r an ki ng o f a g iv en p ar a m et e r . A n a l y si s i s t h e ns i m p l e: t h e l a r g er t h e s pr ea d, t he m or e s en si ti vethematrix parameter is. For waterflooding and gasi n je c ti o n, R F s e ns i ti v it i es a r e a n a l y ze d a t t h e t i m eo f b re ak t hr ou gh a nd a t t he t i me o f u l ti m at e r e-c ov e ry , a s uf f ic i en tl y l o ng t i me a ll o wi n g t he a s-s e ss m en t o f t h e h y d ro c ar b on v o l um e l e ft b e hi n db e ca u se o f s t ra t ig r ap h i c r e as o ns ( t y p ic a l ly 5 0 y r i n

t h i s s t ud y ). T h e t i m e o f u lt im at e r ec ov er y i s a ls oreferred to as the trapped-hydrocarbon time in ther e ma i nd er o f t hi s a rt i cl e . R e co v e ry f a c to r s e ns i t iv -i t ie s a r e e v al u at e d a t t h e t r ap pe d- h yd r oc ar bo n

Figure 14.(A) Recovery factorand (B) water-cut profiles simu-lated as a function of the chan-nel shale drape coverage (CSC)parameter for the waterfloodingrecovery mechanism. The base-case CSC value (60%) corre-sponds approximately to themost likely (P50) value in thecumulative probability distribu-tion shown in Figure 10B. FCindicates that the fine-scale case(full-detail model without up-scaling) is flow simulated. STOIIP =stock tank oil initially in place.

Figure 15.(A) Recovery factorand (B) gas-oil ratio profiles sim-ulated as a function of the chan-nel shale drape coverage (CSC)parameter for the gas-injection

recovery mechanism. The base-case CSC value (60%) corre-sponds approximately to the mostlikely (P50) value in the cumulativeprobability distribution shown inFigure 10B. FC indicates that thefine-scale case (full-detail modelwithout upscaling) is flow simu-lated. STOIIP = stock tank oil ini-tially in place. MSCF/STB = 1000standard cubic foot per stock-tankbarrel.



25/34

time in the sensitivity study conducted for thedepletion recovery mechanism.

Sensitivity charts are displayed in Figure 16for waterflooding, inFigure 17for gas injection,and inFigure 18for depletion. Statistical informa-tion that emphasizes the central tendency (mean andmedian) and significance (p= 0.85) of simulationresults is superimposed on sensitivity charts. A

joint analysis of sensitivity charts for RF at thebreakthrough time (RFbt) and RF at the trapped-

hydrocarbon time (RFth) yields a grouping ofthe matrix parameters into high-importance (H),intermediate-importance (M), and low-importance(L) categories for a given recovery mechanism(Table 6). In this analysis, a parameter is assignedH if it exceeds the p= 0.85 significance criterioneither in the RFbtor the RFthsensitivity chart. Inother words, the joint set ofmatrixparameters that

exceedp = 85 significance level in RFbtor RFthsen-sitivity charts constitutes the set of H parameters.

Figure 16. (A) Sensitivity of the breakthrough-time recovery factor for waterflooding simulations. (B) Sensitivity of the trappedhydrocarbontime recovery factor for waterflooding simulations. See Tables 1and2for descriptions of the parameters. (Median [p=0.50; dashed line in the left-hand side]; [p= 0.85; dashed line in the right-hand side]).

Figure 17. (A) Sensitivity of the breakthrough-time recovery factor for gas-injection simulations. (B) Sensitivity of the trappedhydrocarbontime recovery factor for gas-injection simulations. See Tables 1and 2 for descriptions of the parameters. (Median [p=0.50; dashed line in the left-hand side]; [p= 0.85; dashed line in the right-hand side]).

Alpak et al. 275


26/34

Intermediate importance parameters are selectedanalogously but using the median as the criterion.The remaining parameters form the set of Lfactors.

DISCUSSION OF RESULTS

Sensitivity Structure

It is crucial to underline that the set of importantmatrix parameters that affect the recovery effi-ciency are also a strong function of the recoverymechanism applied to extract hydrocarbons fromthe subsurface. Therefore, before constructing astatic model, one has to pay special attention to thetype of fluidextraction process that will be si-

The Impact of Fine-scale

Documents

Transcript of The Impact of Fine-scale