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GEOPHYSICS, VOL. 74, NO. 2 �MARCH-APRIL 2009�; P. WA35–WA50, 19 FIGS., 4 TABLES.10.1190/1.3073760

coustic and petrophysical properties of a clastic deepwater depositionalystem from lithofacies to architectural elements’ scales

oger M. Slatt1, Eric V. Eslinger2, and Staffan K. Van Dyke3

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ABSTRACT

An analysis of acoustic, petrophysical, and stratigraphic heter-ogeneities has been completed at three scales for an outcropping/subcropping deep-water stratigraphic sequence: lithofacies�core/plug�, lithostratigraphic unit �well log�, and architecturalelement �seismic�. Measurement techniques/instruments includ-ed outcrop measured sections; behind-outcrop drilling/logging/coring �and subsequent core and log analysis�; ground-penetrat-ing radar; shallow seismic reflection; and electromagnetic induc-tion. At the lithofacies scale, four rock types are defined: �1�heterogeneous sandstones and �2� uniform sandstones, whichdiffer in their grain composition and sedimentary structures, butdo not differ significantly in average porosity, permeability, andacoustic impedance; and �3� organic-rich shales and �4� organic-poor shales, which exhibit significantly higher acoustic imped-ance than either sandstone type. There is an inverse relation be-tween porosity and permeability versus acoustic impedance of

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he lithofacies at this scale. At the lithostratigraphic unit scale,hree units of interbedded lithofacies are defined: �1� uniformandstone prone, �2� heterogeneous sandstone prone, and �3�hale prone. Successive merging of thinner beds with thickereds results in clear differences in average rock properties be-ween the lithostratigraphic units, but there is insufficient varia-ion about the averages to preclude statistically significant differ-ntiation of the sandstones. Lithostratigraphic unit propertieslso vary laterally. At the architectural element scale, two archi-ectural elements are channel element and lobe element. Onlyellbore acoustic impedance differs significantly between these

wo elements. However, the internal lateral architecture of thesewo elements is quite different. The results highlight the difficul-y in evaluating stratigraphic patterns away from the wellbore.

ore research in this area is warranted. Attempts to quantify lat-ral variability of properties in a geologically realistic manner arencouraged because lateral variability is as important to reservoirharacterization and performance as is vertical variability.

INTRODUCTION

The senior author of this paper was invited to the 2007 Rainbowonference to present an overview of scales and types of stratigraph-c heterogeneities that might occur in oil and gas reservoirs. To dohis for a largely geophysical audience, an attempt was made at theonference, as well as for this paper, to describe the heterogeneitiesn terms of geophysical characteristics rather than stratigraphic de-criptors, such as upward-fining and upward-coarsening sequences,ouma beds, stratigraphic pinchouts, etc. In a geophysical sense,

his is similar to Hart’s �2008� differentiation of physically signifi-ant seismic attributes �i.e., attributes thought to respond to or direct-y image changes in acoustic or elastic properties� from stratigraphi-

Manuscript received by the Editor 1April 2008; revised manuscript receiv1University of Oklahoma, Institute of Reservoir Characterization, Norman2Eric Geoscience, Inc. and the College of St. Rose,Albany, New York, U.S3Nexen Petroleum U.S.A., Inc., Dallas, Texas, U.S.A. E-mail: staffan�vand2009 Society of Exploration Geophysicists.All rights reserved.

ally significant attributes �seismic attributes that capture changes inaveform shape that are caused by changes in stratigraphy�.Because stratigraphic properties, such as thickness, interlayering

f strata, porosity, and permeability, change laterally as well as verti-ally, so will the seismic response. For example, Hart �2008� citeshe wide range of values of net to gross and other characteristics ofrchitectural elements of a submarine fan that can occur laterally andertically, thus affecting the seismic waveform in ways that can beifficult to predict or interpret. Conversely, changes in seismic fre-uency �and other variables� will affect the seismic signature of atratigraphic feature �Zeng and Kerans, 2003; Hart, 2008�. Geosci-ntists and reservoir engineers often resort to geostatistical tech-iques �variograms, etc.� to accommodate the difficulty of character-

vember 2008; published online 11 March 2009.oma, U.S.A. E-mail: rslatt@ou.edu.ail: e.eslinger@gmail.com.exeninc.com.

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zing or quantifying lateral variations in stratigraphic properties foreological and reservoir modeling, Thus, it is important to be able todentify lateral variability of stratigraphic sequences and their seis-

ic response, in addition to vertical heterogeneity �or homogene-ty�, which is a common geophysical focus �i.e., anisotropy: “… lay-red bedding in sedimentary formations…” �McGraw-Hill Dictio-ary of Scientific and Technical Terms, 2003�.

An outcrop stratigraphic interval, which has been studied in detailor more than 10 years, was chosen to provide examples of strati-raphic variability and accompanying variability in acoustic andetrophysical properties. To compare rock properties according toheir scale �and measurement technique�, the stratigraphic intervalas subdivided into three hierarchical scales: lithofacies, lithostrati-raphic unit, and architectural element scale. In terms of remote de-ection �i.e., identification by some means other than whole core de-cription�, these three scales roughly translate into core-plug scale,ell-log scale, and seismic-reflection scale. The scales are definedore fully later in this paper, but it is important to mention that the

erminology of this threefold subdivision of stratigraphic units is not

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igure 1. �a� Topographic map of the spine 1 and spine 2 area in Wyoc� View looking south of the eastern part of spine 1. North-facing sihe spine 1 and spine 2 area, shows two master channels with externahannel sandstones and associated, smaller internal levees. The chan

onsistent throughout the literature. For instance, lithofacies haseen used to represent the well-log scale with a finer scale existing athe core-plug scale �Curtis, 2002�.

STUDY AREA AND FIELD DATA COLLECTION

The data set was compiled from spine 1 outcrop and the immedi-tely adjacent shallow subsurface. Spine 1 is an outcrop of the Creta-eous Dad Sandstone member of the Lewis Shale in Wyoming,.S.A �Slatt et al., 2008� �Figure 1�. The data set has been compiledver 10 years by obtaining more than 120 outcrop stratigraphic sec-ions, a 550-m long behind-outcrop well that was logged and cored,round-penetrating radar �GPR� surveys, a hammer-seismic-reflec-ion survey, and an electromagnetic-induction survey �summarizedn Slatt et al., 2008�. The outcrops provide a degree of ground truth inefining vertical and lateral heterogeneities at a variety of scales thats not usually possible with a subsurface data set consisting only ofell logs �because of a lack of bed form, bed style, and other deposi-

ional features, as well as limited vertical resolution� and seismic-re-

nd location of the CSM strat test #61 well. �b� Spine 1 outcrop area.hannel Sandstone I is labeled. �d� Geological model, developed fors �modified from Slatt et al., 2008�. Within each channel are sinuousosits are underlain by two lobe �splay� sandstones.

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ection lines or volumes �because of limited vertical resolution�Slatt, 2000�.

Spine 1, a ridge that stands above an adjacent valley floor �Figure�, is composed of 10 lenticular sandstones, separated by shales,hich are sufficiently resistant to modern erosion processes to formbackbone �Witton, 1999� �Figures 1b and c and 2a�. The sandstonesre interpreted as deep-water �turbidite� channel sandstones encasedn thin-bedded turbidite levee/overbank deposits that form what isommonly termed a leveed-channel complex. In general, channelodies comprise one architectural element and levees comprise aeparate architectural element; both are readily imaged seismicallyn the subsurface and form many important reservoirs worldwideWeimer and Slatt, 2006� �Figure 1d�. Here, net sandstone of the lev-ed-channel complex measured along the spine averages 60%, butaries laterally within the confines of the channel complex owing tohe lenticular geometry of the outcropping channel sandstones �Vanyke et al., 2006� �Figure 2c�.A third architectural element underlies the leveed-channel com-

lex. This element is laterally continuous, deep-water lobes �Figuresd and 2c� that can be traced in outcrop for up to 6.0 km and correlat-d with subsurface wells for many more kilometers �Witton, 1999�.obe bodies �also termed sheets, frontal splays, and lowstand fans�re also readily imaged on the seismic reflection record and formany important subsurface reservoirs worldwide �Weimer and Slatt,

006�.A northwest-southeast 2D hammer-seismic line, shot at the top of

pine 1 �cf. spine 1 in the northwest part of Figure 1a and OU seismicine in Figure 2a� provides an excellent image ofhe internally discontinuous nature of the internalhannels �individual discontinuous seismic re-ections� comprising the leveed-channel depositnd the underlying, more laterally continuousobe sandstones �lobe �splay� in Figure 1 and theontinuous seismic reflections below the yellowhannel deposits in Figure 3�. Acquisition of theine was designed so that it crossed the 550-mell �termed the Colorado School of Mines

CSM� strat test #61 well�, which was drilledrom the top of spine 1 �Figures 1a, 2a and b, anda�. A suite of conventional logs and a boreholemage log were obtained from the well, alongith continuous core from 50- to 180-m depth,

nd a smaller cored interval of 265–275-m depthFigure 2b�. This well was used to calibrate theeismic line and also to correlate the seismic lineo 10 outcropping channel sandstones �details ofeismic acquisition and well-log calibration arerovided by Van Dyke et al., 2006� Figures 2bnd 3�.

From the outcrop, 121 stratigraphic sectionsere measured and described at the cm�scale for

edimentary textures, structures, and stratifica-ion style �Van Dyke et al., 2006�. These sectionsorm the basis for characterizing each of the 10andstone bodies and the entire leveed-channelomplex. Witton �1999� also measured six, long,utcrop, stratigraphic sections that included thenderlying lobe bodies and the leveed-channelomplex �Figure 2c�.

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A critical boundary between the leveed-channel complex and thenderlying lobe bodies occurs at 137 m in the wellbore �Figure 2�nd at 140 ms on the seismic line �at the location of the wellbore�Figure 3�. This boundary is the base of a master channel that con-nes the 10 internal leveed channels within a 0.5-km-wide channelomplex approximately perpendicular to the interpreted channelxes �Slatt et al., 2008� �Figure 1d�.Asecond spine — 1 km south ofpine 1, termed spine 2—also is present but is not part of this studyFigure 1d�.

Spines 1 and 2 are separated by external levee-overbank strataharacterized by alternating fine-grained, thinly laminated sand-tones, siltstones, and claystones. In addition to the external levee-verbank deposits, internal levees associated with each of the 10hannel sandstones are also present. Levee-overbank deposits areess resistant to erosion than channel sandstones so that they formalleys on both sides of spine 1 �Figure 1a� and enhance topographicelief between the channel complexes �Figure 1a-d�.

HIERARCHICAL SUBDIVISIONAND DEFINITION OF UNITS

ithofacies

Lithofacies is defined as “a lateral, mappable subdivision of a des-gnated stratigraphic unit, distinguished from adjacent subdivisionsn the basis of lithology, including all mineralogic and petrographicharacters, and those paleontologic characteristics that influence the

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levation map showing the distribution in 3D space of the 10 channelSandstone I �ChS-1� is labeled. Estimated location of the master

the dashed line. Locations of the CSM strat test #61 and the hammer-e are also shown. Width of the channel complex is approximatelyay log and core gamma scan �gray� of the CSM strat test #61 well.the locations of the lithofacies sampled for petrophysical and acous-hree measured stratigraphic sections along spine 1 �along the trackbrown line� and correlations of the channel sandstones �modified

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ppearance, composition, or texture of the rock” �Bates and Jackson,980�. Lithofacies comprise laminae ��1 cm thick� or beds ��1 cmhick�, which typically are deposited during a single event. Thoughmall in scale, lithofacies and their contained laminae and beds arehe fundamental building blocks of reservoirs that control the stor-ge and flow capacity of fluids by the arrangement and distributionf pores, pore throats, and grain-scale barriers. Properties measuredt the core-plug scale, such as porosity and permeability �and some-imes acoustic properties�, are considered here to be representativef a given lithofacies.

Although standard well logs �i.e., excluding micrologs� generallyave a vertical resolution of about a meter, the clustering procedureshat we use to discriminate differences in rock types break out bedss small as the digitizing interval, which for this study was 0.03 m.hus, herein we consider these thin beds to be at the lithofacies scale.

n this context, the core-plug data and the thin beds that are generatedrom the clustering runs are at the lithofacies scale.

ithostratigraphic unit

A lithostratigraphic unit is a rock body composed of a certainithologic type or combination of types, deposited under a given setf environmental conditions �Bates and Jackson, 1980�. In the con-ext of this paper, it is used to describe thicknesses of interbeddedithofacies, specifically interbedded sandstone-shale intervals, usu-lly several meters thick.

Lithostratigraphic units also exert control on reservoir perfor-ance, such as by the presence or absence of stratigraphic seals

e.g., shales atop sandstones�, lateral pinchouts of sandstones intohale, etc. Lithostratigraphic units are normally measured and de-cribed from whole core or well logs.

rchitectural element

Architectural element is defined as a distinct body or assemblagef sediment bodies with lower and upper confining boundaries that

a)

b)

igure 3. �a� Inverted relative acoustic impedance profile across spination of the CSM strat test #61 well. Numbers refer to the individualb� Interpreted seismic relative impedance profile. Numbers refer toellow is sandstone and light blue is thin-bedded internal levees. Dotradational and lateral migration trends of channel sandstones.

re genetically related to each other and generated in a common dep-sitional setting �Brookfield, 1977; Allen, 1983; Miall, 1985; Pick-ring et al., 1989; Sprague et al., 2002; Sprague et al., 2003�. Theyre the larger features of a stratigraphic sequence with discrete sizes,eometries, trends, volumes, and internal arrangement of lithostrati-raphic units. In this paper, we have imaged and described architec-ural elements using standard outcrop stratigraphic sections, GPRbtained at a frequency of 100 MHz, electromagnetic inductionEMI� obtained at a frequency of 1–20 kHz, and a 2D hammer-seis-ic-reflection line obtained at a frequency of 28 Hz.

ubseismic- and seismic-scale subdivisions

The various scales of measurement described above are subdivid-d into those considered to be subseismic lithofacies and lithostrati-raphic units �beneath normal marine acquisition of 2 to 60 Hz�, andhose that can be seismically resolved, i.e., architectural elements.

e realize that there is not a clear boundary between these twocales, that subsurface features that might not be seismically resolv-ble under one set of conditions �e.g., depth of burial, acquisition pa-ameters, etc.� might be resolvable under another set, and that vastmprovements continue to be made in geophysically resolvingmaller and smaller stratigraphic heterogeneities �Chopra and Mar-urt, 2007�. 3D seismic-reflection volumes, coupled with well data,re the common tools for describing architectural elements in theubsurface.

PROPERTIES OF SANDSTONEAND SHALE LITHOFACIES

There are four basic lithofacies comprising the Dad Sandstone atpine 1, two sandstones and two shales. A description of the mea-urements made on representative samples from these lithofacies isade first, and then the lithofacies are discussed along with a com-

arison of their properties.Core-plug porosity and permeability measure-

ments were made from the sandstones by routinemethods and at atmospheric pressure. Results aresummarized in Table 1. In addition, four coreplugs from each of the two sandstone lithofacieswere analyzed for acoustic properties. Bulk den-sity was measured directly on the core plugs bydetermining the weight �mass� and volume ofeach plug. Back calculation of grain densitiesbased on the independently measured bulk densi-ty and porosity values for each sample gave arange of 2.68–2.72 g/cm3, with an average of 2.70g/cm3; these values are typical of sandstones withthe mineralogic composition described by Thyneet al. �2003�. Velocity measurements were madeby direct traveltime measurement for the givenlength and density of each plug; berea sandstoneand aluminum were used as standards. Acousticimpedance was derived from these measuredP-wave velocities and bulk densities. Results aresummarized in Table 2.

Measurements of properties from 12 shale coreplugs from the CSM strat test well, reported byCastelblanco-Torres �2003�, are used in thisstudy. Clay minerals �dominantly illite, with less-

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r smectite, kaolinite, and chlorite� generally comprise �50% of thehales, with 25–50% quartz plus feldspar, and �10% carbonate.wo types of shale lithofacies were defined for this paper on the basisf total organic carbon �TOC� content. Seven of the plugs have TOCalues of 0.5–0.7 wt.% and five plugs have values of 1.4–1.7%.hese two types of shales are termed organic-poor shales �OrgP-sh�

�1% TOC� and organic-rich shales �OrgR-sh� ��1% TOC�, al-hough we recognize that such shales are not truly organic rich inerms of hydrocarbon source rock potential.

For the shale plugs, porosities were measured at ambient pres-ures and permeabilities were measured at 500 psi �Castelblanco-orres, 2003�. Bulk density and velocity were measured at 500 psi.o directly compare the shales with the sandstones measured at am-ient pressures, Castelblanco-Torres �2003� measurements were in-reased by 6%, a value determined by two additional stressed mea-urements. Results are summarized in Table 2.

andstone lithofaciesLewis Shale sandstones, of which the Dad Sandstone is represen-

ative, are generally fine to medium grained, poorly to moderately

able 1. Average and standard deviations of porosity andermeability of US and HS lithofacies based upon 109ore-plug measurements. Measurements were made attmospheric pressure.

Lithofacies # n Porosity �%� Permeability �mD�

niform Sandstone Lithofacies �US�

3 64 28�1 188�124

15 30 28�4 421�281

eterogeneous Sandstone Lithofacies �HS�

12 13 29�4 396�25

8 2 25�8 497�702

able 2. Averages and standard deviations of properties measithofacies. Values for shale lithofacies were obtained by Catletmospheric pressure. Shale permeabilities were measured atith sandstone properties.

Porosity�%�

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verage 29.5

tandard deviation �1.1

eterogeneous Sandstone Lithofacies �HS� 4 core plugs

verage 29

tandard deviation �2.3

rganic l � l Poor Shale Lithofacies �OrgP-sh� 8 core plugs

verage 18.4

tandard deviation �2

rganic l � l Rich Shale Lithofacies �OrgR-sh� 4 core plugs

verage 14.6

tandard deviation �0.7

orted, angular to subangular, subarkose to arkosic arenites �Thynet al., 2003�. Framework composition consists of 50–70% detrital,onocrystalline quartz, with lesser amounts of plagioclase, sedi-entary lithic grains, micas, and organic matter. Clay matrix

2–12%� is formed mainly by disaggregation of shale lithic grainsuring early burial compaction �i.e., pseudomatrix�. Cements con-ist of calcite, quartz, and clay.

The two types of sandstones differ primarily in the presence or ab-ence of sand to pebble-sized shale lithic clasts within the beds �Fig-re 4�. When present, the shale clasts occur within a sandstone ma-rix.

A secondary, significant difference is that sandstones that do notontain lithic clasts are often uniformly bedded �i.e., massive� with-ut significant cross-bedded or slumped strata, in contrast to thelast-bearing sandstones �Figure 3�. In this paper, we refer to thelast- and sedimentary structure-bearing sandstones as heteroge-eous sandstones �HS� and the clast-free, uniformly bedded sand-tones as uniform sandstones �US�.

S lithofacies

US exhibit little variability in sedimentary textures, structures,nd stratification at the single-bed scale. Individual sandstone bedsre in direct contact with other sandstone beds across amalgamationurfaces �Figure 4�. Average properties are given in Table 1, basedpon 94 plug measurements of two groups of US, labeled as lithofa-ies #3 and #15 �the reason for this subdivision is explained in a laterection�.

The four plugs from which acoustic properties were measured arerom core depths of 138–140.5 m �log depth 137–139 m� and66–268 m �log depth 264.5–267 m� �Figure 2b� �Table 2�.

S lithofacies

HS exhibit interval variability in textures and sedimentary struc-ures as described above �Figure 4�. Average properties of HS are

n selected core plugs representative of the two sandstone-Torres (2003). All porosity measurements were made ati and corrected to atmospheric pressures for comparison

eabilityd�

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301 �0.49 �294 �193

162 2.69 3735 1896 1.94 9444

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iven in Table 1, based upon 15 plug measurements. The four plugsrom which acoustic properties were measured are from core depthsf 48–50 m �log depth 46.5–48.5 m� and 125–126.5 m �log depth23.5–125 m� �Figure 2� �Table 2�.

omparison of US and HS lithofacies at the core-plugcale

It is apparent from the larger group �Table 1� and smaller groupTable 2� of porosity and permeability measurements that porositynd permeability are about equivalent between the two sandstones.ulk densities are equivalent for the two sandstone types, but-wave velocities, and thus acoustic impedance values, are slightlyigher for HS than for US �Table 2� because of shale clasts in theandstones.

hale lithofacies

rgP-sh lithofacies

The core-plug interval of OrgP-sh lithofacies chosen for analysis135.4–137.5-m core depth; 134–136-m log depth� comprises theaminated shale immediately above the base of the master channelFigures 2b and 5�. Measured parameters for eight core plugs are list-d in Table 2.

rgR-sh lithofacies

The core-plug interval of OrgR-sh lithofacies chosen for analysisomprises the shale deeper within the stratigraphic section �279–85-m core depth; 280–282.5-m log depth� �Figure 5�. Core exami-ation reveals occasional vague lamination. Measured parametersor the four core plugs are listed in Table 2.

138 m

140 m

50 m

48 m

Unstratified Sandstone(US)

Heterogeneous Sandstone(HS)

igure 4. Core of the US and HS sandstones. Black dots on core areocations of core plugs for porosity and permeability measurementsTable 2�. Core depths are in meters. Features in the core of HS in-lude slump, shale-clast conglomerates, erosional scour surfaces,nd cross-beds. Compare this with the featureless characteristics ofhe US core.

omparison of OrgP-sh and OrgR-sh lithofacies at theore-plug scale

Comparing the two shales at the core-plug scale, OrgP-sh exhibitsigher average porosity, two orders of magnitude higher averageermeability, and a greater range of permeability than OrgR-sh �Ta-le 2�. Bulk density, sonic velocity, and acoustic impedance valuesre equivalent between the two �Table 2�.

omparisons of core-plug properties of sandstones andhales

At the core-plug scale, sandstones exhibit higher average porositynd permeability values than shales �Table 2�. Bulk density and son-c velocity values, and consequently acoustic impedance values, are

uch higher for shales than for sandstones.Because porosity and permeability are desirable properties to be

etermined from seismic-reflection data, comparisons were madeetween core-plug porosity and acoustic impedance and from core-lug permeability and acoustic impedance, both from the eight sand-tone and 12 shale core plugs �Table 2�. The resulting trend lines andorrelation coefficients �Figure 6� show that at least at the core-plugcale, porosity and permeability are inversely related to acoustic im-edance.

LITHOSTRATIGRAPHIC UNITS

dentifying lithostratigraphic unitsLithostratigraphic units represent the next higher scale within the

rilled stratigraphic sequence �Figure 2a and b�. To evaluate vertical

282 m 135 m

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igure 5. Typical core of the OrgR-sh and OrgP-sh. Core depths aren meters.

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stratigraphic� variations in properties at this and higher scales, arobabilistic-clustering procedure �PCP� was used to combine dif-erent lithofacies into successively thicker groups of strata basedpon similarity in properties. Clustering procedures within the PCPan be used to divide samples into probabilistically defined groupsithin which samples have similar properties. Specifics of the clus-

ering methods and ancillary supporting routines for single- andultiwell studies are being prepared for publication �E. V. Eslinger,

ersonal communication,�. Clustering variables can include well-og data and core data plus any other depth-related parameter thatan be digitized �Eslinger et al., 2004a, 2004b; Eslinger and Everett,005�.

The work flow used for this study is described here. First, a clus-ering run was made using three well logs as clustering variables —ulk density �RHOB�, gamma ray �GR�, and inverted sonic transitime �1/DT, converted to m/s�. Fifteen groups �clusters, or modes�ere requested. Because only well-log curves were used as vari-

bles, the resulting 15 clusters could be termed electrofacies, butere we consider them to be equivalent to lithofacies. Contiguousamples assigned to the same lithofacies define a bed, and the thin-est bed possible is the digitizing interval �0.03 m�. The choice of 15ithofacies was somewhat arbitrary; more or fewer could have beensed. However, the intention was to generate a sufficiently detailedlassification that would result in the definition of beds that were ap-roximately the same scale that might be defined in a typical core de-cription. Using more lithofacies results in a more detailed classifi-ation �more thin beds� than use of fewer lithofacies.

The 15 lithofacies are listed in Table 3, arranged according to theirell-log gamma-ray response �increasing down the column�. Data

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3000 4000 5000 6000 7000 8000 9000 10000 11000

igure 6. Crossplots showing inverse the relation between core-lug-measured permeability �logarithmic scale� and porosity versusore-plug-derived acoustic impedance. Linear equations and corre-ation coefficients are shown.

abulated include an assigned lithofacies number, the lithofaciesype �either sandstone, siltstone, or shale based on gamma-ray logesponse�, the percentage of �digitized� samples assigned to eachithofacies, the number of core plugs from each lithofacies, and the

ean gamma-rayAPI well-log response for each lithofacies. Four ofhe lithofacies were also assigned to a lithostratigraphic unit basedn prior study of the whole core. Specifically, lithofacies #3 and #15elong to the lithostratigraphic unit that contains mainly US mixedith shale lithofacies and lithofacies #8 and #12 contain mostly HS

ithofacies, also combined with shale.A bed-thickness filter �BTF� routine within the PCP �Eslinger,

007� was then used to merge lithofacies beds so any bed thinnerhan a user-defined thickness was eliminated. Beds thinner than the

inimum permitted thickness were then added to either the overly-ng or the underlying lithofacies bed, with the decision based on arobability matrix argument. The probability distribution of eachample in the thin bed is compared with the probability distributionsn a user-defined interval at the bottom of the overlying bed and at theop of the underlying bed. Specifically, two dot products are comput-d using the probability distributions as vectors and the resulting dotroducts are treated as a similarity index that dictates whether thehin bed is assigned to the overlying or the underlying bed �Eslinger,007�. Each BTF computation produces a merged or upscaled real-zation of the original beds. A given BTF run can be made on theriginal, unfiltered stack of beds, or on a previously filtered stack. Inhis exercise, each run was made on the original unfiltered stack.uring a series of runs in which the minimum bed thickness is suc-

essively increased, the scale gradually changes from the lithofaciescale to the lithostratigraphic unit scale and then to the architecturallement scale. As BTF thickness is increased with successive BTFomputations:

able 3. Fifteen arbitrarily defined lithofacies for theAMLS clustering run. Shown are the defined lithofacies,

he percentage of each lithofacies of the total stratigraphicnterval, the number of core plugs from which porosity andermeability data were obtained, the mean well-logamma-ray API value for the lithofacies, and the color coden Figures 8 and 17.

ithofacies # Lithofacies % # Plugs GR �mean� Color

15 US 4.25 30 70.2 yellow

1 SS 1.2 0 71.5 gold

3 US 10.98 64 77.5 orange

13 Sltstn? 6.8 0 97.5 lt grn

2 Sltstn? 11.86 30 88.3 med grn

10 Sltstn? 0.66 0 89.3 dk grn

12 HS 5.01 13 94.4 white

9 Sltstn? 0.8 0 101.1 gray

8 HS 12.73 2 111 purple

6 Sh 10.55 0 119.1 gray

11 Sh 6.08 0 123.8 gray

4 Sh 7.17 0 128.3 gray

14 Sh 8.18 0 123 gray

7 Sh 2.27 0 137.2 gray

5 Sh 11.44 0 142.5 black

a

b

F�a

Fbtmaster channel �Figure 2�.

WA42 Slatt et al.

• Fewer beds remain �Figure 7a�.• The average bed thickness for each lithofacies

increases �Figure 7b�.• Some lithofacies disappear.• The original properties of any remaining

lithofacies might change as the original litho-facies are merged.

For example, by adding beds of shale lithofa-cies to a stratigraphic interval that was originallycomposed entirely of US beds, the thickness ofthe lithostratigraphic unit increases while theadded properties of the shales progressively alterthe average properties of the sandstones. In thesame manner, as more sandstone beds are addedto a lithostratigraphic unit originally composed ofshale, then the thickness of the lithostratigraphicunit will increase and the average properties ofthe shale will more closely approach those of asandstone unit.

Identified lithostratigraphic units

As mentioned in the previous section, for theCSM strat test number #61 data set, the BTF pro-cess was applied to the 1D stack of 524 beds de-fined in the initial clustering run. A first BTF runafter the clustering run, beginning with 15 litho-facies �column A in Figure 8� was designed toeliminate beds thinner than 1.5 m thick �column Bin Figure 8�. This BTF run reduced the total num-ber of beds from the original 524 to 115 �Figure7a�. Additional BTF runs were made with theminimum bed thickness permitted increasingwith each run, and with each run operating on theoriginal stack of 524 beds. With each successiverun, the average bed thickness of each lithofaciestended to increase as the number of lithofacies de-creased �Figure 7b�.

Additional BTF runs were completed to suc-cessively eliminate beds thinner than 3 m, 6.1 m,12.2 m, 24.4 m, 61 m, and 122 m �columns C, D,E, F, G, and H in Figure 8, respectively�. The finalBTF run �column H in Figure 8� resulted in threeremaining intervals, which basically representlithostratigraphic units that are amalgamations ofthe original 15 lithofacies. These three remainingintervals, from top to bottom, originated �prior toBTF� as HS lithofacies #8 �purple in Figure 8�,US lithofacies #3 �orange in Figure 8�, and Shlithofacies #5 �black in Figure 8�. Figures 7 and9–14 show what happens to the properties ofthese three original lithofacies during successivestages of BTF. Similar plots could be made for theother 12 original lithofacies, but here we justtrack changes in the three main lithofacies, US,HS, and Sh �combined OrgP-sh and OrgR-sh� toillustrate trends that occur during the successive

ee lithofaciesrease in aver-

y eliminatingck, �f� 24.4 me base of the

)

)

igure 7. �a� Crossplot showing the reduction in numbers of beds of the thrUS, HS, and Sh� with successive BTF runs. �b� Crossplot showing the incge bed thickness with successive BTF runs.

igure 8. �a� The initial 15-mode PCP run and results of applying the BTF beds thinner than �b� 1.5 m thick, �c� 3 m thick, �d� 6.1 m thick, �e� 12.2 m thihick, �g� 61 m thick, and �h� 122 m thick. The horizontal line at 137 m is th

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Clastic heterogeneities WA43

TF runs. Below, we apply the terminology US prone, HS prone,nd Sh prone in the discussion of the three lithostratigraphic unitshat we track.

Prior to filtering, the sum thickness of lithofacies #3, #5, #8, #12,nd #15 �Table 3�, identified as belonging to these three lithostrati-raphic units �US prone, HS prone, and Sh prone�, was only 44% ofhe total stratigraphic thickness in the CSM strat test #61 well. Thether 56% of the total interval was initially composed of the other 10ithofacies. These 10 lithofacies were merged into the three finalithofacies �US prone, HS prone, and Sh prone� during the succes-ive BTF runs because of similarities in well-log properties amongets of lithofacies.

The gamma-ray API trends provide the simplest example to showhe effects of merging of beds during the BTF runs �Figure 9�. Theh-prone lithostratigraphic unit exhibits the highest average gam-a-rayAPI values, and the US-prone lithostratigraphic unit exhibits

he lowest average gamma-rayAPI values �Figure 9�. The HS-pronenit lies between these two lithostratigraphicnits because of a combination of the presence ofhale clasts in individual HS beds �termed dis-ersed shale by geophysicists� and because ofhale lithofacies interbedded with the sandstoneithofacies �termed laminar shale by geophysi-ists�. For the same reason, with each successiveTF run, average API values of the Sh-prone

ithostratigraphic unit decrease as more beds ofandstone are incorporated into them, and APIalues of the US-prone lithostratigraphic units in-rease slightly as more beds of shale are incorpo-ated into them �Figure 9�. Although there is aood separation of API values at all BTF runsmong the three lithostratigraphic units, statisti-al variability �standard deviation� indicates theossibility of some potential overlap in API val-es among the units �Figure 9�.

A plot of BTF bed thickness versus well-logverage bulk density �Figure 10a� shows that atll BTF thicknesses, the Sh-prone lithostrati-raphic unit has a significantly higher densityhan the two sandstone-prone units, as is the caset the core-plug, lithofacies scale �Table 2�. How-ver, there is a bulk density crossover at 12.2-mTF thickness where HS-prone average bulkensity goes from being higher than that of theS-prone unit to being lower. Figure 8 helps ex-lain how this can happen. The HS lithofacies isolored purple �mode 3 of the PCP run� in Figure. Prior to any BTF, only about one-third of theection above the horizontal orange line at 137 ms assigned to the HS lithofacies. But, with suc-essive BTF runs, increasing amounts of otherithofacies are merged with the original HS litho-acies so the resulting bulk density of the amal-amated lithofacies changes. It is apparent thatncreasing amounts of lithofacies with lower bulkensities were added to the original BTF facieshrough the first five BTF runs.

A somewhat similar trend is apparent for sonicelocity �Figure 10b�. The velocities were com-uted as the arithmetic mean of the inverse of the

Figure 9. Crostratigraphic ustandard devia

a)

b)

Figure 10. Crvelocity responumbers at easonic velocity

lowness �DT� values. Average velocity of the Sh-prone lithostrati-raphic unit is greater than those of the sandstone-prone units. Aver-ge velocities of US-prone units are higher than those of HS-pronenits, and the spread between values at each BTF thickness above2.2 m is large, even though the standard deviation values suggest ahance of overlap in this property.

The end result of this bulk density-velocity combination is that,or any BTF thickness, the acoustic impedance of the Sh-proneithostratigraphic unit is highest, followed by the US-prone unit,hen HS-prone lithostratigraphic unit �Figure 11�. The spread of val-es between the two sandstones at any BTF thickness above 12.2 ms large, but the standard deviations suggest a chance of overlap inhis property. Shale-prone and HS-prone lithostratigraphic units aretatistically different, but that is not the case for shale-prone and US-rone lithostratigraphic units.

Because the PCP subdivides and combines lithofacies based uponhe combination of well logs, similar computations can also be made

howing the variation in gamma-ray log response of the three lithos-th successive BTF runs. The � numbers at each data point are theout that average data point.

t showing the variation in well-log �a� bulk density and �b� sonicthe three lithostratigraphic units with successive BTF runs. The �point are the standard deviation about that average data point. Themputed as the inverse of the slowness �DT log�.

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WA44 Slatt et al.

ith the core-plug porosity and permeability data because they werencluded in the log ASCII standard files associated with depths, justs were the well-log depths. Figure 12a and b shows that HS-pronenits have lower porosity and permeability averages at thin BTFhicknesses, but reverse trends with increasing BTF. This change ap-ears to be associated with the crossover from higher to lower bulkensity for HS-prone lithostratigraphic units with increasing BTFhickness �i.e., lower bulk density equates to higher porosity and per-

eability �Figure 10a��. Even though there is a good spread of valuest each BTF thickness for porosity, and to a lesser extent for perme-bility, there is sufficient overlap in standard deviation values suchhat the differences are not statistically significant.

In the plots of porosity and logarithm of permeability versus BTFed thickness �Figure 12a and b�, there is only one data point for the

igure 11. Crossplot showing the variation in well-log acoustic imphe three lithostratigraphic units with successive BTF runs. The � noint are the standard deviation about that average data point.

)

)

igure 12. Crossplots showing the variation in �a� porosity and �b� peric scale� of the three lithostratigraphic units with successive BTF r

t each data point are the standard deviation about that average data pf the �horizontal-plug� permeabilities was computed, and then thehese logarithmic values was used.

h-prone lithostratigraphic unit, at the 122-m BTF run. This is be-ause there are no plug samples within the shales �except for thoseisted in Table 2, which were not used in the BTF runs� below a depthf 274 m �Figure 8�, and it is not until the last BTF run that the evolv-ng Sh-prone lithostratigraphic unit incorporated a depth intervalithin which core plugs were taken. Specifically, at the last 122-mTF run, a sequence of lithofacies #15, belonging to the US-prone

ithostratigraphic unit �yellow in Figure 8�, became incorporatednto the Sh-prone lithostratigraphic unit. Between 262 and 267 m,his lithofacies #15 consists of homogeneous sandstone with perme-bilities approaching 1000 mD.

The inclusion of these high-reservoir quality sandstone samplesnto the Sh-prone lithostratigraphic unit caused its arithmetic meanermeability at the 122-m BTF run to actually be higher �at log 10

perm � 2.5� than the mean permeabilities of ei-ther the US-prone �log 10 perm � 2.1� or theHS-prone �log 10 perm � 2.2� lithostratigraphicunits �Figure 12b�. This is perhaps a prime exam-ple of how a thin, high-reservoir quality unit thatis resolvable at the lithostratigraphic unit �well-log� scale might be missed at the architectural ele-ment �seismic� scale.

As noted, the lithostratigraphic units are mostvariable up to a BTF thickness of 12.2 m. Abovethis BTF thickness, the properties usually varywithin �10% with increasing BTF thickness. Inother words, above this critical thickness, whichcoincidentally is about the same thickness as aseismically resolvable stratigraphic interval,there is much less change in rock properties thanat BTF thicknesses below 12.2 m.

ARCHITECTURAL ELEMENTS

The three architectural elements comprisingspine 1 are channel-fill deposits, levee deposits�not analyzed in this paper�, and lobe deposits�Figure 1d�. The base of the master channel, at adepth of 137 m �450 ft� in the CSM strat test #61well �Figures 2a and b and 3�, corresponds to theboundary between the HS-prone lithostrati-graphic unit above and the US-prone lithostrati-graphic interval below as defined by the 122-mBTF run �column H, Figure 8�. Shale-pronelithostratigraphic units occur from a depth of279 m to the base of the core. Thus, the boundarybetween the two major intervals defined by the122-m BTF run is coincident with the boundarybetween the two main architectural elements. Atthis scale, the two architectural elements can bedefined by the set of properties that are based onthe well control �Table 4�. Of the properties com-pared, the only one that has a wide spread of val-ues at this scale is acoustic impedance US � HS,which is the opposite of the relationship at thelithofacies scale �Table 2�. Yet as discussed in thesummary, the architectural arrangement of bedsand lateral properties is quite different.

e response ofs at each data

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Clastic heterogeneities WA45

ummary

The above analysis of wellbore data shows variations in verticalroperties at the architectural element scale; however, in the statisti-al sense, most differences are not significant because of overlap intandard deviation values.

LATERAL PROPERTIES OFLITHOSTRATIGRAPHIC UNITS

AND ARCHITECTURAL ELEMENTS

ateral characterization of a single channel sandstone

Based upon field observations, differences in the lateral �as well asertical� arrangement and variability in lithofacies and lithostrati-raphic units are quite noticeable. These differences will affect res-rvoir performance, so in an analog reservoir, it is essential to definehe lateral attributes in 2D, or preferably 3D, space as best as possi-le, and preferably with hard data.Accurately de-ning lateral attributes can be a difficult task ifata, including seismic data, are sparse. In this re-ard, outcrop data may be useful, as demonstrat-d by Sullivan et al. �2000� for a field in the Gulff Mexico.

For our study, sufficient 3D data have been ob-ained from only one of the channel sandstoneshat comprise spine 1. This particular sandstone isamed Channel Sandstone I, the lowermost chan-el sandstone of the 10 comprising spine 1 �Fig-re 2a and c�. This sandstone is composed of USnd HS lithofacies, so it can be considered as aithostratigraphic unit according to our definition.

Channel Sandstone I has been characterizedn 3D space using a variety of geological andeophysical techniques. It is exposed in threeimensions as east-facing �north-south trend� andorth-facing �west-east trend� outcrops �Figurea-d; Figure 14�. The east-facing outcrop is50-m wide and oriented in a direction that is ap-roximately perpendicular to its depositional diprientation �Figures 1d and 13a�. The longitudi-al outcrop extends for approximately 300 m in aorth-facing, east-west �parallel to depositionalip� orientation �Figures 1c and 13a and c�. Theast-facing outcrop is particularly significant be-ause it exhibits a laterally asymmetric distribu-ion of lithofacies �Figure 15b�. Along the50-m-wide face, HS lithofacies occurs on itsorth side and near the base of the outcrop �Figure3b and c�. US lithofacies occurs across the top ofhe outcrop �Figure 13b and c�.Athird lithofacies,rossbedded sandstone, occurs on the south sidef the outcrop �Figure 13b and c�. Because it hasore-derived properties similar to US lithofacies,or the purpose of this paper, it is considered USithofacies. The proportion of US to HS averages0% and 40%, respectively, along this outcrop.owever, HS is not uniformly distributed lateral-

y across the outcrop, but rather decreases in

Table 4. Avelobe architec

Property

Gamma ray �

Bulk density

Sonic velocit

acoustic impe

Core plug po

Core plug pe

Cross-bedde

Southwesa)

b)

c)

Figure 13. �a�cies distributiand debris flocies. To the lelithofacies. Thstones with anthree sandstonbidites and sh

bundance toward the south end of the outcrop �Figure 13b�. There-ore, lithostratigraphic properties are also going to vary laterally.

To illustrate the internal lateral variability of this lithostrati-raphic unit, two behind-outcrop GPR lines �Figure 14a-c�, and 12easured stratigraphic sections �Van Dyke, 2003� were obtained

long the outcrop. These data provided average estimates of 80% USnd 20% HS. Various characteristics of sinuous channel depositslso were imaged by the GPR lines; features include lateral accretionurfaces, slumps, and onlap surfaces �Figure 14b�. Such features areound in larger subsurface leveed-channel reservoirs �Abreu et al.,003�.

Two boreholes �labeled 1 and 5 in Figure 15� were also drilled andamma-ray logged to depths of 3-7 m in front of the east-facing out-rop. These and other boreholes in the same area were used to cali-rate the GPR lines and lithofacies by 1D convolutional modelingYoung et al., 2007�. These boreholes were drilled after an EMI sur-ey had been run and had detected additional sandstone stratigraphi-

and standard deviations of properties of the channel andlements.

Channel architecturalelement

Lobe architecturalelement

106�16 90�20

� 2.27�0.12 2.27�0.06

2327�252 2674�131

��g/cm3��m/s�� 5292�267 6070�347

%� 28.5�4.2 27.6�2.3

lity �md� 175�310 135�115

Red = shale-clast cong. Brown = sandy debrites

tone Massive sandstoneInterbeddedturbidites andshale-clastconglomerates

Northeast

150 m

Massive sands w/fluid escape structures

ed sands

raph of the east-facing outcrop of Channel Sandstone I. �b� Lithofa-g the rock outcrop: to the right, the rocks are interbedded turbiditele-clast conglomerate� beds, here classed as HS sandstone lithofa-rocks are massive to cross-bedded sandstones, here classed as USmetry of lithofacies is typical of sinuous deep-water channel sand-

cutbank-like side and an inner point-bar-like side. �c� Pictures of thes: cross-bedded sandstone, massive sandstone, and interbedded tur-t conglomerates.

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WA46 Slatt et al.

cally beneath Channel Sandstone I, which wascovered by thin soil �Stepler et al., 2004� �Figure15b�. Gamma-ray logs and cuttings from bore-holes 1 and 5 provided estimated sandstone/shaleproportions of 67/23% and 83/17%, respectively.A second EMI survey to the west �Figure 15ashows the location of the survey� revealed a bendof the channel sandstone into the outcrop, furthersupporting the sinuous character of this channelsandstone �Stepler et al., 2004; Slatt et al., 2008�.

Based upon core and outcrop features, thecomplexity of HS lithofacies is interpreted as aresult of slumping and erosional processes thatare common to such channel systems �Weimerand Slatt, 2006�. Specifically, shale clasts that arecontained within HS sandstone in Channel Sand-stone I are generally thinly laminated. They ap-pear to be blocks of associated levee beds that hadslumped into the channel where they probablythen mixed with sandy-sediment gravity flowsmoving down the channel to form the slumpedand shale-clast-bearing sandstones comprisingHS �Figure 4�. This observation supports the seis-mic-reflection images of slump scars along outerbends of sinuous channels, reported by Posamen-tier and Kolla �2003�, and demonstrates a similar-ity in deep-water sinuous channels and fluvialmeandering channels, whereby the outer bend is apoint-bar-like area. By contrast, the US across thechannel from the HS �Figure 13� represents depo-sition along a point-bar-like inside bend of thesinuous channel.

Summarizing all of this information leads tothe conclusion that there is significant lateral vari-ability in US and HS lithofacies, and between thesandstones and shales along and across ChannelSandstone I. Most important though is the com-plexity of the stratification as revealed by theGPR lines �Figure 15a-c�. It is these variationsthat will play a significant role in fluid flow be-havior in a subsurface reservoir analog, yet maynot be considered important if the properties mea-sured at the wellbore are mainly considered influid-flow modeling.

Comparison with a seismically definedleveed-channel deposit

A cross-sectional seismic image of a Gulf ofMexico leveed channel �Figure 16b�, which is ofa similar width as Channel Sandstone I �Figure16a�, provides an example of variability within achannel fill that is similar to that of Channel Sand-stone I. This line shows an asymmetric leveedchannel with thicker levee wedge and steeperlevee margin on its right side than on its left side,suggesting the right side is the outer cutbank-likeside of a sinuous channel �Weimer and Slatt,2006; Slatt et al., 2008�. Thus, the more steeplydipping seismic reflections that downlap toward

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b

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igure 14. �a� Aerial photograph of Channel Sandstone I showing the locines a-b and b-c that show the key architectural features of Channel Sandars for a-b and b-c are shown in those figures. �b� Base of channel, overllast conglomerate beds �encased in red�, slumped beds, and dipping lateeds. �c� Base of channel and overlying radar-transparent shale-clast conglencased in red�, and bedded sandstones.

Channel Sandstone 1Sandstone

Shale

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GPR lines

Top surface of ChannelSandstone 1

5 1

0 60API

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Gamma ray loboreholes 1 an

EMI Survey 1

Shalier

Sandier

1400 001000 00900 00800 00700 00600 00500 00400 00300 00200 00125 0075 0025 00

–100 00–400 00–800 00

c)b)

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igure 15. �a� Same aerial photograph as in Figure 14, but with the addition of two EMI surveys and the positions of boreholes 1 and 5 �labeled dots�.ween wells 1 and 5 is approximately 150 m. �b� EMI survey image beneaurface in front of Channel Sandstone I showing the termination of that sanray color, and a second sandstone in the lower left �bright colors�. �c� Gamm

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Clastic heterogeneities WA47

he channel floor on the steep, outer side of the channel are interpret-d to be slumped HS beds and the more gently dipping beds to theeft are point-bar-like sandstones. It is anticipated that reservoir fluidow would vary across this channel because of these differences.his example illustrates the point made by Hart �2008� that whenvaluating potential fluid-flow properties of a reservoir, attentionhould be paid to its seismic-reflection �stratigraphic� patterns asell as its rock properties, measured at a wellbore. A basic under-

tanding of the type of deposit comprising the reservoir, and its for-ative processes, is quite useful for interpreting such significant

tratigraphic features.

haracterization of leveed-channel and loberchitectural elements

eneral

The 2D seismic line across the top of spine 1 indicates consider-ble lateral stratigraphic variability within the entire leveed-channelomplex �Figures 1d, 2c, and 3�. The 10 channel sandstones appearo be at least partially offset-stacked and they have associated inter-al levee beds alongside, above, and below them. Without more thanne 2D seismic line, it is not possible to quantify the lateral variabili-y of the entire leveed-channel complex, although the approximateistribution of sandstone and levee deposits is interpreted in Figureb. However, one way to partially quantify the combined effect ofateral and vertical attributes of a leveed-channel complex is by cal-ulating its effective vertical permeability, as described below.

alculating effective vertical permeability �Kve�

Schuppers �1993� published the following equation, which relatesateral and vertical attributes of an architectural element:

Kve � �Kss��A�/�1 � Nsh�L/4��2,

here Kve � effective vertical permeability, Anet/gross, Kss � standstone �horizontal� per-

eability, Nsh � number of shales per meter oftrata, and L � average shale length or width �m�Note: all shales are assumed to have K � 0.�

Kss, A, and Nsh are values that can be deter-ined at the wellbore. For the leveed-channel

nd lobe architectural elements in the CSM stratest #61 well, Kss used is the respective values athe BTF of 122 m �Table 4� and A was estimatedrom the gamma-ray log �Figure 4�.

To obtain estimates of Nsh it was necessary toetermine the number of shale beds along corednd uncored portions of the CSM strat test well.o do this, the PCP was used to determine thetratigraphic distribution of US, HS, and Sh litho-acies in the well for the leveed-channel and loberchitectural elements. This PCP analysis wasnitialized �calibrated� using six short intervalsithin the overall cored interval of the well by re-

ating the lithofacies to their respective well-logignals, using the bulk density �RHOB�, neutronNPHI�, gamma-ray �GR�, and sonic transit time

a)

b)

C

100ms

Figure 16. Coposit as imagebounded on bothe channel arping reflection

DT� logs. Because there were six intervals from the core used forhe model, the clustering results generated six lithofacies �two eachor US, HS, and Sh� and this was done throughout the depth rangesed in the clustering run. That is, the model developed betweenell-log signal and the six short-cored intervals permitted lithofa-

ies to be predicted for the noncored intervals. This supervised �i.e.,alibrated using core data� initialization contrasts with the unsuper-ised �i.e., core data not used for calibration� initialization used forhe clustering run discussed above in which 15 lithofacies were de-ned prior to the BTF filtering.For the CSM strat test well, the resulting cluster run over the depth

nterval 11–275 m identified the stratigraphic �vertical� distributionf the lithofacies throughout the well �Figure 17�. It is worth notinghat the PCP independently verified outcrop observations �Slatt etl., 2008� that HS is the predominant sandstone lithofacies above the37-m depth of the master channel �i.e., the leveed-channel architec-ural element�, and US is the predominant sandstone lithofacies be-eath the master channel �i.e., lobe architectural element�.

ve of leveed-channel architectural element

For the leveed-channel architectural element, the equation wassed to calculate Kve for a variety of shale lengths �L� from 10 m upo 200 m, which is the maximum cross-sectional width of the lev-ed-channel architectural element �i.e., at its top, flattened on 0 msWT �Figure 3�. The measured parameters that were held constantre Kss � 175 mD, A � 0.64, and Nsh � 0.53 �73 shale beds in37-m total thickness of leveed-channel complex; from Figure 17�.he lengths can be considered possible lengths of shale within theaster channel that might affect fluid flow in an analog reservoir of

quivalent size �such as shown in Figure 18�. Results of the calcula-ions �Figure 18� show that as L increases, Kve decreases exponen-ially, which illustrates the effect of shale lengths on the internal ar-hitecture of this element and potential effects on reservoir perfor-ance.

dded sandstonet-bar side)

Shale-clast conglomerates(cutbank side)

150 m

250 m

on of �a� Channel Sandstone I and �b� subsurface leveed-channel de-ertical seismic line from the Gulf of Mexico. The seismic channel iss by levee wedges. The steeply dipping reflectors on the right side ofpreted as slumped, shale-clast conglomerates and the shallow dip-e left side of the channel are interpreted as bedded sandstones.

ross-be(poin

mparisd on a vth sidee inters on th

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FsOu�wmcDyke et al., 2006; Slatt et al., 2008�.

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WA48 Slatt et al.

ve of lobe architectural element

For the lobe architectural element, the measured parameters thatere held constant are Kss � 135 mD, A � 0.90, and Nsh � 0.56

79 beds in 140 m from Figure 17�. Separate Kve calculations wereade for the same Lvalues as for the channel sandstone architectural

lement. Lobe sandstones near spine 2 extend for lengths up to20 m �Minken, 2004�, but the Kve calculated for this L is onlylightly smaller than that for L � 200 m so is not included in Figure8. Results show a similar relation between Kve and shale length asas computed for the leveed-channel architectural element; Kve de-

reases exponentially with an increase in shale length �Figure 18�,gain demonstrating the potential importance of lateral attributes inffecting reservoir performance.

CONCLUSIONS

In this paper, we have documented the variability in importantroperties at three different scales within a deep-water leveed-chan-el/lobe outcrop analog of a common deep-water reservoir type. Thehree scales — lithofacies, lithostratigraphic units, and architecturallements — correspond to core-plug, well log, and seismic scales inerms of properties measured �using different techniques and instru-

ents�. A generalized plot showing the process used to describe thehree scales is shown in Figure 19. The concepts developed from theesults reported here can be directly applied to better understandeep-water reservoir characteristics from seismic-reflection vol-mes.

� Lithofacies scale. Two sandstones comprise the lithofacies inthis stratigraphic sequence, one that is uniformly bedded�termed US� and one that is internally complex and heteroge-neous �termed HS�. At this scale, porosity and permeability areabout equivalent between the two sandstones. Acoustic imped-ance values are also equivalent for HS and US �Table 2�.Two shale lithofacies are also present within the stratigraphicsequence, one �OrgR-sh� that contains more organic matter andis more massively bedded than the other �OrgP-sh� that is finelylaminated and probably slightly coarser grained. The OrgP-shlithofacies exhibits higher porosity, two orders of magnitudehigher average permeability, and a greater range of permeabili-ty than the OrgR-sh lithofacies.

igure 19. Schematic illustration of the method of characterizationnd upscaling used in this paper. Lithofacies scale data are obtainedrom core plugs. Lithostratigraphic unit data are defined by a cluster-ng procedure that divides samples into probabilistically definedroups within which samples have similar well-log properties, thenuccessively adds thinner beds to thicker beds and calculates theirverage properties.Architectural element data are obtained by the fi-al merging of beds into the dominant types within the thicker strati-raphic sequence. In terms of scales, the lithofacies scale covers aery small range ��1 m�, the lithostratigraphic unit covers a rangef meters to tens of meters, and the architectural element covers aange of �100 m.

ithofacies

Six lithofaciesfor calibration

GAMLS-predictedlithofacies

GRD (Raw)

0 (GAPI) 200

US-2

US-1

HS-2

HS-1

OrgP-sh

OrgR-sh

0 ft

500 ft

1000 ft

0 ft

500 ft

1000 ft

(91 m)

(183 m)

(274 m)

igure 17. Gamma-ray log from the CSM strat test #61 well and thetratigraphic positions of the lithofacies �US, HS, OrgP-sh, andrgR-sh�. Based upon calibration of well-log patterns to core datasing the geologic analysis via maximum likelihood systemGAMLS�, the lithofacies were identified in uncored portions of theell. The HS lithofacies dominates in the channel interval above theaster channel and the US lithofacies dominates below the master

hannel. These trends were verified by outcrop observations �Van

igure 18. Calculated effective vertical permeability �Kve� for differ-nt values of shale length �L� for channel and lobe architectural ele-ents. The two trends are virtually identical.

2

3

NwppMafhi�Snch

A

A

B

B

C

C

C

E

E

E

E

H

M

M

M

Clastic heterogeneities WA49

Sandstones are more porous and permeable than shales �as ex-pected�. Shales exhibit much higher acoustic impedance valuesthan sandstones. Good inverse correlations are established be-tween acoustic impedance, and core-plug permeability andporosity.

� Lithostratigraphic units. Lithostratigraphic units are combina-tions of lithofacies. Three lithostratigraphic units are defined,termed US prone, HS prone, and Sh prone, because of the typeof lithofacies that dominate each unit. A cluster analysis pro-gram was used to evaluate the effects on properties of thelithostratigraphic units by combining different lithofacies, be-ginning with 15 different lithofacies defined by specific re-sponses of a combination of gamma-ray, sonic velocity, andbulk density logs, and ending with three lithofacies also definedby combined log responses. This merging or upscaling processresults in the following trends: �1� average bed thickness in-creases while the number of beds decrease because of sequen-tial merging of beds of given thicknesses; �2� gamma-ray APIvalues follow the pattern: Sh � HS � US, the relation betweenthe two sandstone types being a result of the presence of shaleclasts within HS sandstone beds �dispersed shale� and mergingof shale beds with sandstone beds �laminated shale�, which in-creases the average API value of sand-prone lithostratigraphicunits; �3� acoustic impedance follows the pattern Sh � US �HS owing to systematic variations in bulk density and sonic ve-locity as beds are merged; and �4� average sandstone porosityand permeability values follow the pattern HS � US. In mostinstances, there is a wide spread in average properties at a givendegree of merging of beds, but there is the potential for somestatistical overlap based upon standard deviation calculations.Cross-channel variability of one channel lithostratigraphic unitis quite obvious in outcrop in terms of the distribution of HSand US, and the net sandstone content. This lateral variability isdifficult to quantify in a meaningful fashion owing to nonsys-tematic average variations in the rock properties that resultfrom depositional processes and limited wellbore control.

� Architectural element. Architectural elements are combina-tions of lithostratigraphic units. In this example, there are threearchitectural elements, channel complex, lobe sandstone, andlevee complex; only the first two were investigated for thisstudy. Comparison of lithostratigraphic units that are merged orupscaled to the architectural element scale exhibit meaningfuldifferences in properties that are measured from wellbore data,but only acoustic impedance averages are significantly differ-ent statistically. However, the two architectural elements are in-ternally quite different in arrangement of lithofacies and lithos-tratigraphic units. Our results show that when evaluating poten-tial properties of a reservoir, attention should be paid to strati-graphic patterns in addition to physical or petrophysical pat-terns that are measured at the wellbore.The results of this study show that standard rock propertiesmeasured at the wellbore vary depending upon their internalcomposition, but there is sufficient variability in measurementsthat most differences are not statistically significant. Lateralvariability at the lithostratigraphic and architectural elementscales are important parameters that will affect the flow of flu-ids in a reservoir, and thus, the performance of the reservoir.At-

tempts to quantify lateral variability of properties in a geologi-cally realistic manner are encouraged because this variability isas important to reservoir fluid flow and performance as verticalvariability.

ACKNOWLEDGMENTS

The authors extend their sincere appreciation to David R. Pyles,eil F. Hurley and the many other people and supporting companiesho R. M. Slatt has worked with for several years on the Lewis Shaleroject. Much has been learned about this formation since theroject began in the late 1990s while Slatt was at Colorado School ofines. Slatt would also like to thank Andrew M. Slatt for compiling

ll of the statistical and other information into informative graphicsor this paper. S. Van Dyke would like to thank John DeLaughter foris critical review of geophysical material and his continued mentor-ng over the years. E. V. Eslinger would like to thank Alan CurtisBHP-Billiton� for numerous discussions concerning upscaling.eismic interpretation was accomplished on Seismic Micro Tech-ologies Kingdom 8.2 software. Core-plug measurements wereompleted in the Poro-Mechanics facility at the University of Okla-oma by YounaneAbousleiman and John Brumley.

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