High Frequency Characterization of an Outcropping, Sinuous Leveed-Channel Complex, Dad Sandstone Member, Lewis Shale, Wyoming

Reservoir Characterization: Integrating Technology and Business Practices 771

High Frequency Characterization of an Outcropping, Sinuous Leveed-Channel Complex, Dad Sandstone Member, Lewis Shale, Wyoming

Van Dyke, S.University of OklahomaAera Energy LLC

Slatt, R. M.University of Oklahoma

Dodson, J.University of Oklahoma

Valerio, C.University of OklahomaOccidental Oil and Gas Corp.

Buckner, N.University of Oklahoma

Correa-Correa, H.University of OklahomaShell Oil Corp.

Ojo, B.University of OklahomaSchlumberger Inc.

Abstract

This paper presents the results of data collection,analysis, and integration to build a 3D geologic modelof an outcropping leveed-channel complex. Data isfrom more than 120 standard measured stratigraphicsections, behind-outcrop drilling/logging/coring,ground-penetrating radar and electromagnetic inductionsurveys, and 2D shallow seismic reflection acquisition.

This leveed-channel complex, which is part of theDad Sandstone Member of the Cretaceous Lewis Shale,Wyoming, consists of ten channel-fill sandstones, con-fined within a master channel. The complex is 67m

(200ft.) thick, 500m (1500ft.) wide, and has a net sandcontent of approximately 57 percent. Individual chan-nel-fills are internally lithologically complex, but in asystematic manner which provides a means of predict-ing orientation and width of sinuosity. Although it hasnot been possible to completely document the three-dimensionality of this system, the 3D model that hasevolved provides information on lithologic variability atscales which cannot be verified from conventional 3Dseismic of subsurface analog reservoirs. This verticaland lateral variability can provide realistic lithologic

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input to reservoir performance prediction. An outcomeof this study has been knowledge gained of the extent ofmanipulation required to obtain the spatially correct

geometry and architecture of strata when integratingoutcrop and shallow, behind-outcrop data sets.

Introduction Deep-water, sinuous leveed-channel deposits can

form important oil and gas reservoirs worldwide.Because of their lateral and vertical complexity, theycan be very difficult to produce hydrocarbons (e.g.,Kolla et al., 2001; Beydoun et al., 2002; Navarre et al.,2002; Posamentier and Kolla, 2002; Abreu et al., 2003).Using typical subsurface data, it can be challenging tomodel this level of complexity for reservoir perfor-mance prediction. Thus, either modern or outcropanalogs sometimes are sought to provide the requiredlevel of detail for this purpose. There are excellentexamples of leveed-channel systems on the modern seafloor and shallow sub-bottom; for example, the AmazonFan, Mississippi Fan, and Indus fan (Weimer and Slatt,in press). However, these systems are rarely sampled(i.e. rocks and sediments) in detail, although the side-scan sonar and shallow subsurface seismic images areexcellent. By contrast, outcrop analogs provide theopportunity for detailed rock sampling, but they areoften extensively weathered because of their character-istic fine-grained nature. Outcrop exceptions includesome Ordovician strata in Algeria, Cretaceous CerroToro Formation, Chile, and the Miocene Mt. MessengerFormation, New Zealand (Weimer and Slatt, in press).

Part of the Dad Sandstone Member of the LewisShale in Wyoming is an example of a moderatelyweathered, outcropping, leveed-channel system. It hasbeen studied for several years (summarized by Pylesand Slatt, in press; Slatt et al., in press), mainly becauseit is a fine-grained leveed-channel system similar tothose that produce hydrocarbons (Fig. 1). Because goodoutcrops are sporadic, special attention has been paid toacquiring data to capture the fine- to medium-scale het-erogeneity of this system using a variety of techniques,including standard outcrop stratigraphic sections (Wit-ton, 1999; Bracklein, 2000; Pyles and Slatt, 2000;Witton-Barnes et al., 2000; Minton, 2001; Van Dyke,2003; Gonzalez, 2004; Minken, 2004; Soyinka andSlatt, in press), behind-outcrop drilling/logging/coring(CSM Strat Test Well #61) (VanDyke, 2003; Slatt et al,in press); ground-penetrating radar and electromagneticinduction (Young et al, 2003; Stepler, 2003; Stepler etal, 2004; Correa et al, 2006) and most recently, shallow2D seismic reflection (Witten et al., 2005). When com-bined, these techniques can be utilized to develop a 3Dgeologic model amenable to ‘outcrop reservoir simula-tion’ (Slatt et al., 2000; Goyeneche et al., this volume).In addition, these techniques provide data which aremost commonly used in the petroleum industry (i.e.,

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High Freq. Characterization of an Outcropping, Sinuous Leveed-Channel Complex, Dad Sandstone Member, Lewis Shale, WY

subsurface well logs, cores and seismic), so compari-sons can be made between outcrop features and—inthis case—correlative behind-outcrop, shallow subsur-face data. We have found that this comparison providesa key mental link between outcrops and reservoir (Slatt,2000). This is especially true for those people whorarely examine outcrops, but who work routinely withsubsurface data.

This paper focuses on aspects of the outcrop-behind outcrop characterization that have not previ-ously been published for the Dad Sandstone.Specifically, it has been challenging to integrate the out-crop stratigraphy with the 550m (1700ft.) long, CSM

Strat Test #61 behind-outcrop well and the shallow seis-mic line shot over the wellsite and behind the outcrop(Fig. 2). Below, we discuss the various steps required tomatch the diverse data sets to develop a coherent imageof the behind-outcrop stratigraphy and also discuss thespecial processing of this shallow seismic line requiredto make it suitable for interpretation. It is not possible toentirely verify the resulting 3D geological model fromthe studies cited above and described in this paper.However, the various lithologic complexities associatedwith sinuous leveed-channel complexes are identified ina manner amenable to reservoir performance modelingand prediction.

Dad Sandstone levee-channel systemThe Lewis Shale and associated Fox Hills Sand-

stone and Lance Formation form a third-orderprogradational, non-marine to ‘deep marine,’ mud-dominated, depositional system (Pyles and Slatt, inpress). The Lewis Shale forms the slope facies withinthis system, and the Dad Sandstone member comprisesleveed-channel and sheet sandstones.

The Dad Sandstone in the area of study consistsof 10 channel-fill sandstones which form a resistantridge called Spine 1 (Figs. 1-3) (VanDyke, 2003). Onehundred and twenty one (121) closely spaced strati-graphic sections have been measured along the tensandstones. Locations of the sections, the base and topof each channel-fill sandstone outcrop, and significantfacies boundaries are positioned in 3D space with a dif-

ferentially-corrected TrimbleTM Global PositioningSystem (GPS), which has decimeter scale accuracy.From these data, a 3D architectural facies model has

been built in GocadTM which spatially reconstructs thearchitecture and facies distribution of the 10 channel-fill sandstones (Fig. 3) (VanDyke, 2003).

In outcrop, the areal extent and thickness of thechannels decreases from the basal Channel-fill sand-stone #1 to the uppermost Channel-fill sandstone #10(Figs. 2-3). A second ridge, called Spine 2 (Fig. 1),about 1000m (3000ft.) to the south, is held up by fiveleveed channel-fill sandstones (Minken, 2004). Threescales of heterogeneity have been defined for the areaof these two ridges (Fig. 4) (Slatt et al, in press).

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A shallow seismic line has been acquired at thetop of Spine 1 (Fig. 2). The main object of acquiringthis line has been to determine if a basal master channelis confining the 10 channel-fill sandstones within the

relatively narrow area of 500m (1,500ft.) (Fig. 1). Theresults of the seismic survey are discussed below, afterdescribing the channel-fill sandstones.

Channel-fill lithofaciesEight lithofacies were identified from the outcrop

and shallow borehole studies (Table 1):

F1 sandstone with water-escape structures(some cross-bedded);

F2 structureless sandstone (without water-escape structures);

F3 cross-bedded sandstone (without water-escape structures);

F4 parallel to subparallel laminated sandstone(Bouma Tb);

F5 rippled or climbing-rippled sandstone(Bouma Tc);

F6 shale or mudstone (Bouma Td-e);

F7 shale clast conglomerate; and

F8 contorted and re-sedimented beds.

All facies except F7 and F8 are fine-grained, moder-ately well sorted sandstone and siltstone.

Criteria for defining inside vs. outside bends of sinuous channelsIn the Dad Sandstone, these eight lithofacies are

distributed within channel-fill sandstones in a mannersuggesting some similarities in processes to fluvialmeandering channels (Slatt et al., in press). In particu-lar, some of the channel-fills are composed of shaleclast conglomerates (F7) and contorted beds (F8) onone side and cross-bedded sandstones (F3) overlain bymassive sandstones (both with and without water-escape structures; F1 and F2) on the other side (Fig. 5).Shallow seismic surveys of deep marine sinuous chan-nel systems show slump scars on the outside bends of

channels (Fig. 6). Combining these characteristics, wepropose that the outside bends of channels are erosional‘cutbank-like’ features, and the slumped facies andshale-clast conglomerates (shale clasts are composed ofthinly-laminated F4 lithofacies) represent the channelmargin and proximal levee deposits eroded andslumped into the channel. By contrast, the inside bends,composed of cross-bedded sandstones (F3), are ‘pointbar-like’ features. The overlying massive sandstonesexhibit downlap patterns suggestive of lateral accretionbedding, which occur in point bar and in-channel beds

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(Fig. 5). In addition, electromagnetic induction andground-penetrating radar surveys over Channel-fillSandstone #1 reveal a sharp bend in the sandstone, indi-cating sinuosity (Fig. 7) (Stepler et al., 2004).

These channels probably have fed sand into thedeeper basin contemporaneously with levee formationby overspill (Peakall et al., 2000; Keevil et al., in press).The channels are backfilled during a significantly laterstage of deposition. Features of similar channel-fill

sandstones in other, nearby Dad Sandstone outcropsprovide evidence for this interpretation. These featuresinclude: (1) sharp, erosional and slumped contactsbetween the thin-bedded levee facies and coarser, sandychannel-fill facies (Fig. 8), (2) onlap of the channel fillfacies onto the thin bedded facies (Fig. 8), and (3) theoccurrence of shale clast conglomerates at the bases ofsome of the channels (Fig. 7) (Young et al., 2003).

Estimation of channel sinuosityThe above characteristics were used as an indica-

tor of orientation of sinuosity (Fig.9). To determine thedegree of channel sinuosity, we confined the channelbend to approximately the lateral limits of Spine 1 (app.500m or 1500ft [Fig. 1]), and estimated a ratio of thethalweg length of a single bend wavelength over theaxial length of the same single bend wavelength(Fig. 10). With this calculation, lower numbers repre-

sented less sinuosity (1.0= straight channel), whileprogressively higher numbers represented progressivelygreater degrees of sinuosity.

These values were applied to the ten channel-fillsandstones, resulting in the curved channels illustratedin Figures 11-13 and 15-20; channel parameters aregiven for each channel on each figure.

Description of channel-fill sandstonesBelow are presented brief descriptions of each of

the ten channel-fill sandstones. Details are provided byVanDyke (2003). Each of the sandstones is separated bythin-bedded, very fine sandstone/mudstone strata

(Fig. 2). These thin-bedded strata are considered to belevee beds associated with each of the 10 channel-fillsandstones (Fig. 4).

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Channel-fill sandstone #1

This sandstone, at 11m (34ft.) thick, is the thick-est of the ten channel-fill sandstones (Fig. 2). It is thestratigraphically lowest channel-fill sandstone withinthe Spine 1 outcrop, although sheet sandstones crop outstratigraphically beneath (Witton, 1999). This sand-stone crops out in three dimensions, so has been studiedin more detail than the other sandstones. The base ofthis channel, as mapped from ground-penetrating radarlines (Young et al., 2003), electromagnetic induction(Stepler et al., 2004), and shallow borehole drilling(VanDyke, 2003), is irregular in shape (Fig. 21), andmakes a sharp bend behind the outcrop toward the

southwest (Fig. 7), indicating it is a sinuous channel.Shale-clast conglomerate beds (F7) are interbeddedwith slumped beds (F8) in the northern part of thissandstone, while cross-bedded sandstones (F3) occuron the southern part (Fig. 5). As stated above, thisasymmetric lateral distribution of sandstones indicatesthe northern part is the ‘cutbank’ side of a channel-fill.The southern part of the sandstone represents the inneror ‘point bar’ side of this channel-fill (Fig. 11). Thenorthern channel margin has been removed by post-Cretaceous erosion.


The northern part of this channel-fill sandstone isdominated by shale-clast conglomerates (F7). Thesouthern part contains laterally continuous, cross-bed-

ded sandstone (F3). On this basis, the interpretedorientation of the channel is shown in Figure 12.


Shale clast conglomerates (F7) occur in thenortheastern and southeastern parts of this channel-fill,representing the outer bend of the channel (Fig. 13).

Channel-fill sandstones #4/#5

Channel-fill Sandstones 4 and 5 are amalgamated(Fig. 14). The southernmost part of the lower Channel-fill Sandstone #4 consists of cross-bedded sandstone

(F3) and the northern part contains shale-clast con-glomerate (F7). Overlying the F3 beds along thesouthernmost side is an erosional contact, overlain by

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F7, indicating this is part of separate Channel-fill Sand-stone #5 that is amalgamated to Channel-fill Sandstone

4 (Fig. 14). This dramatic change in orientations of thetwo channels is compared in Figures 15 and 16.


The primary diagnostic facies comprising thischannel-fill is cross-bedded sandstone (F3), indicating

the outcrop is in an area of the inner-side of a channelbend (Fig. 17).


The western part of this sandstone contains faciesF3, and the eastern part contains some slumped facies

F8. The orientation of the channel bend is displayed inFigure 18.


The eastern side of this sandstone is dominatedby shale-clast conglomerate (F7) and the western side

contains cross-bedded sandstone (F3) facies. The orien-tation of the channel bend is displayed in Figure 19.

Channel-fill sandstone #9/#10

These sandstones are small and not well exposed.The northern part contains cross-bedded sandstone (F3)

facies. The orientation of the channel bend is displayedin Figure 20.

Correlation of outcrops with seismic line

Acquisition and processing of seismic line

A behind-outcrop, shallow seismic line was

acquired using a 48 channel Geode recording system

and a sledge hammer and aluminum plate as the source

(Fig. 22). The 28 Hz geophones were spaced 4 m (13 ft)

apart with the source points located between geo-

phones. Two additional sources were established offeach end of the seismic line. The receiver locations and

elevations were mapped with the TrimbleTM differen-tial GPS unit. Source locations and elevations weremapped by interpolating between receiver stations, or

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by extrapolating beyond the stations. This data set wasoriginally processed using a plane-wave technique(Witten et al., 2005). The plane-wave technique wasdeveloped to be fast and easy to use, with less time andexpense than is the case with conventional seismicacquisition techniques (Witten et al., 2005). However,for this seismic line, we applied a more traditional seis-mic data processing workflow, which, althoughrequiring more time and geophysical skill, providesimproved stratigraphic detail to be used in behind-out-crop, shallow seismic studies. Processing was

performed using ProMAXTM software. The sequentialworkflow was as follows:

1. convert from SEG2 to SEGY format, 2. apply geometry, 3. refraction statics, 4. trace balancing, 5. velocity analysis, 6. radon filter (for noise reduction), 7. deconvolution,

8. 2nd iteration velocity analysis, 9. stack, and 10. migration.

After the processing was complete, the logs fromthe CSM Strat. Test #61 well were tied to the seismic

data using Hampson RussellTM software (Fig. 22).

Projection of the channel-fill complex onto the seismic line

In order to spatially project each outcroppingchannel-fill sandstone onto its proper position on the2D seismic line, the following four calculations firsthad to be made for each sandstone:

1. structural dip correction, 2. terrain correction, 3. ground surface slope correction, and 4. depositional dip correction.

Structural dip correction

The structural dip of the sandstones is 12° south-west, so each sandstone must be projected 12° from itsbase to coincide with its actual location on the seismic

line (Fig. 23). Since the seismic line was shot in anorthwest-southeast orientation, the 12° dip does nothave to be corrected for azimuth. Therefore a simpletrigonometric function has been used to calculate theproper depth to which the base of each channel-fillsandstone would project onto the seismic line. Thisdepth also has been converted to two way seismic traveltime (Fig. 22).

Terrain correction

Unlike the structural dip correction, the terraincorrection varies for each channel-fill sandstone. Theseismic line was shot at a ground elevation of (2260m)

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6780ft (Fig. 23). s each channel-fill sandstone crops out

at a different ground elevation, a calculation must be

applied. The outcropping base of Channel-fill Sand-

stone #1 is at an elevation of 2235m (6705ft.) (Fig. 23).

The elevation difference of 25m (75ft.) was converted

to 20ms (Fig. 22) and applied to the seismic line.

Slope correction

This slope correction and the following deposi-

tional dip correction are made to project the proper

location of the channel-fill sandstones as seen in out-

crop and the GocadTM 3D architectural facies model to

their position on the seismic line. Since the seismic line,

by its nature, only records the events directly beneath it,

it does not take into account the depositional dip of the

beds that it records. Since we are trying to project dip-

ping bedding planes that are laterally offset from the

seismic line’s location, these corrections must be calcu-

lated so that their proper location can be determined;

i.e., a sloping bed will occur at different X, Y, Z loca-

tions as its lateral position shifts – this is the

fundamental basis for this correction. This calculation

takes into account the 2° south depositional dip of the

depositional slope (Pyles and Slatt, in press). The far-

thest point from all outcropping channel-fill sandstones

to the seismic line is ~443m (1329ft) (Fig. 23). The

same equation has been used to correct for the 12°

southwest dip was applied for this 2°. Since the seismic

line trends northwest-southeast, an azimuth correction

of 1.5° south has been applied, so that the equation used

is: tan 1.5° x 443m = 11.6m (34.8ft) or ~20ms.

Depositional dip correction

This next correction is superfluous; however, its

recognition is important to mention. Because the struc-

tural dip of beds is 12° southwest, the outcrop face is at

an angle to true depositional dip. The thickest part of

Channel-fill Sandstone #1 from its base to its top is

11.6m (34ft) in the stratigraphic plane, so the calcula-

tion to determine the true vertical depth is (cos12o x

11.6m) = 11.1m (33.25ft) or ~20ms. Since this correc-

tion is 97.8 percent of the original value for the

maximum thickness of any channel-fill sandstone, this

calculation is discarded. For example, the average

thickness of the other channel-fill sandstones is 3.3m

(10ft) or 10ms (Fig. 2), which is equivalent to the thick-

ness of a wavelet exhibited on the seismic line. Thus,

the wavelet approximates the thickness of all of the

individual channel-fill sandstones with the exception of

the thicker Channel-fill Sandstone #1.

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Projection of the master channel and Channel-fill Sandstone #1 onto the seismic line

The seismic line was acquired principally todetermine whether a master channel was present whichwould have confined the ten channel-fill sandstones to anarrow portion of the sea floor during deposition. Basedupon calibration of the CSM Strat Test #61 well syn-thetic seismogram to the seismic line (Fig. 22), and thepresence of truncated reflections on the seismic line, amaster bounding channel was identified across the seis-mic line (Fig. 24). The master channel is beneath thebase of Channel-fill Sandstone #1, which is the strati-graphically lowest channel-fill sandstone in outcrop

(Figs. 2 and 24). Witton (1999) showed that the base ofChannel-fill Sandstone #1 occurs at approximately 83m(250ft) (90ms TWT) at the outcrop. However, the cal-culations for all projection corrections presented in thispaper indicated that the base of Channel-fill Sandstone#1 could occur as deep as 110-120ms TWT [e.g., 25m(~30ms) + 80m (~80ms) = 105m or 315ft ~ 110ms].Coupling these two interpretations allowed us toapproximate the basal portion of Channel-fill Sandstone#1 between 90 and 120ms TWT) (Fig. 24).

Projection of the other channel-fill sandstones onto the seismic line

For the projection of the other channel-fill sand-stones onto the seismic line, a 30:1 width:height ratio isused (Clark and Pickering, 1996). The sinuosity of eachchannel-fill sandstone is projected to the location of theseismic line (Figs. 11-13 and 15-20). The thickness ofeach sandstone is converted to two-way travel time, andthe assumption is made that this thickness remains con-stant over the distance of the outcrop. Since each

sandstone (except Channel-fill sandstone #1) is aboutthe thickness of a wavelet peak (3.3m or 10ft. or 10ms),wherever a peak crosses the seismic line, it shouldclosely represent the X,Y, Z position of one of the chan-nel-fill sandstones seen in outcrop, at that same two-way travel time (depth). Crossing points of each chan-nel-fill sandstone at the seismic line are listed inTable 2.

3D geological model of the Spine 1 leveed-channel systemDetailed interpretation of 3D seismic horizon

slices has documented the laterally offset and verticallystacked characteristics of subsurface sinuous leveed-channel systems (Fig. 25). What is more difficult toevaluate from seismic intervals is the lithologic vari-

ability that is imaged, since closely spaced wells are notdrilled within these systems, nor is their sufficient seis-mic resolution to image small-scale features, eventhough such features can effect reservoir performance.Overlay of the ten Dad Sandstones channel-fill sand-

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stones comprising Spine 1 shows similarities tosubsurface examples, but adds knowledge of the litho-logic variability at multiple scales (Fig. 4).

In this case, the ten channel-fills are confined lat-erally within a 500m (1500ft.) swath owing to thepresence of a master channel during their deposition(Fig. 24). Both the lateral (Fig. 25) and vertical(Fig. 26) distribution of the channel-fill system is verycomplex. Most of the channel-fills are vertically com-partmentalized owing to the presence of intervening

thin-bedded, finer grained, internal levee deposits; thiscompartmentalization comprises Level II heterogeneityin Figure 4. Similarly, the lateral lithologic variabilitywithin any one channel-fill has been documented, andis expressed as Level III heterogeneity in Figure 4. Thelithologic detail provided at both levels can not bereadily obtained from subsurface data, so this outcropprovides an analog for in-putting realistic lithologic het-erogeneities into a 3D geologic model for reservoirperformance prediction.

Conclusions

This paper presents the results of data collection,analysis, and integration to build a 3D geologic modelof an outcropping leveed-channel system. Although the3D model has only been partially documented, it pro-vides the basis for inputting realistic lithologicparameters into production performance simulations ofsubsurface analog reservoirs. It is important to note thatthe scale of the model is of the same magnitude as sub-surface leveed-channel deposits and reservoirs (for

example, Fig. 25). To build the outcrop model from adiverse outcrop and behind-outcrop, shallow subsurfacedata set requires considerable manipulation of the X, Y,Z coordinates of outcrop and behind-outcrop points toobtain the spatially correct geometry and architecture ofthe system.

This extra effort is essential for building realisticgeologic models from outcrop/behind-outcrop charac-terizations for subsurface application.

Acknowledgements

All of the authors except R. M. Slatt and J. Dod-son contributed research presented in this paper whilegraduate students in the School of Geology and Geo-physics at University of Oklahoma. Funds for theresearch were provided by Conoco-Phillips Co., ShellInternational Exploration and Production, and Total

Exploration and Production Inc. Seismic processing

was performed under an academic license agreement

with Landmark Graphics, Inc. for ProMAXTM. Logs

from the CSM Strat Test #61 well were tied to the seis-

mic data using Veritas DGC's Hampson RussellTM

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package. Andrew Slatt completed many of the graphicsand Carol Drayton edited the paper for clarity, style,and format.

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Slatt, R.M., H.A. Al-Siyabi, C.W. VanKirk, and R.W. Will-iams, 2000, From geologic characterization to “reser-voir simulation” of a turbidite outcrop, Arkansas,U.S.A., in A.H. Bouma and C.G. Stone, eds., Fine-Grained Turbidite Systems: AAPG Memoir 72/SEPMSpecial Publication 68, p.187-194.

Soyinka, O.A., and R.M. Slatt, in press, Identification andmicro-stratigraphy of hyperpycnites and turbidites inCretaceous Lewis Shale, Wyoming: Sedimentology.

Stepler, R., 2003, Three-dimensional imaging of a deepmarine channel beneath outcrop with electromagnetic

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induction and ground penetrating radar; CarbonCounty, South-central Wyoming: University of Okla-homa M.Sc. thesis.

Stepler, R.P., A.J. Witten, and R.M. Slatt, 2004, Three dimen-sional imaging of a deep marine channel-levee/over-bank sandstone behind outcrop with electromagneticinduction and ground penetrating radar: The LeadingEdge, p. 974-978.

Van Dyke, S., 2003, Fine scale 3D architecture of a deepwa-ter channel complex, Carbon County, South-centralWyoming: University of Oklahoma M.Sc. thesis,.

Weimer, P., and R.M. Slatt, in press, Introduction to thepetroleum geology of deepwater depositional systems:AAPG Special Publication.

Witton, E.M., 1999, Outcrop and subsurface characterizationof the Lewis Shale, Carbon County, Wyoming: unpub-lished M. Sc. thesis, Colorado School of Mines, 214p.

Witton-Barnes, E.M., N.F. Hurley, and R.M. Slatt, 2000, Out-crop and subsurface criteria for differentiation of sheetand channel-fill strata: Example from the Cretaceous

Lewis Shale, Wyoming: GCSSEPM Foundation 20th

Annual Bob F. Perkins Research Conference, p. 1087-1105.

Witten, A.J., B.R. Witten, and R.M. Slatt, 2005, Seismicreflection processing by plane-wave synthesis: Journalof Geophysics and Engineering, v. 2, p. 1-7.

Young, R.A., R.M. Slatt, and J.G. Staggs., 2003, Applicationof ground-penetrating radar imaging to deepwater(turbidite) outcrops: Marine Geology, v. 20, p. 809-821.

Table 1. Facies Descriptions (applies to any one channel).

Facies Description and Average Abundance (%)

F1 (blue) Sandstone with water-escape structures (average: 20%)

F2 (yellow) Structureless sandstone (without water-escape structures) (average: 53%)

F3 (magenta) Cross-bedded sandstone (average: 21%)

F4 (dark gray) Parallel to sub-parallel laminated sandstone (average: 4%)

F5 (dark green) Rippled or climbing-rippled sandstone (average: 1%)

F6 (blue-violet) Shale or mudstone (average: trace)

F7 (red) Shale clast conglomerate (average: 4%)

F8 (white) Slumped beds (average: 1%)

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Table 2. Shot-point locations of channel-fill sandstones across the seismic line.

Channel-fill sandstone Shot point locations of channel margins

Master channel Entire seismic line

#1 215-257

#2 203-250

#3 Does not intersect seismic line

#4 209 -251, while the crossing points for #5

#5 257-295

#6 248-294



#9/10 204-257

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Figure 1. (C) shows the north-south trending Lewis Shale outcrop belt in Wyoming (A). Arrows are dominant pale-ocurrent directions measured from sedimentary structures. Red box shows the main location of the study, which is

enlarged in (D) and (E). Beds dip 12o to the southwest. The locations of the Spine 1, Spine 2, and Rattlesnake Ridgeoutcrops are shown in (D). (B) An orthophoto projection in 3D showing Spines 1 and 2 and the distribution of the chan-nel-fill sandstones (E).

A

B C

Sheet (FrontalSplay) SS

Thin-beds

Channel SS

12o

D

E

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Figure 2. 3D digital elevation model of Spine 1 with the different colors representing elevations (see bar scale at bottomof figure). The 10 channel-fill sandstones are shown in brown in their spatially-correct positions. Maximum thicknessesof each channel sandstone and intervening shale are tabulated, from which Net Sandstone was calculated. Vertical yel-low line is the location of the CSM Strat Test #61 well. Orange line is the location of the N-S trending 2D seismic linediscussed in this paper. Red dashed line is the position of a master channel predicted prior to seismic acquisition.

Channel Max. Max. Sand. Sh.Thick. (ft.) (ft.)

10: 8

9: 8

8: 12

7: 1019

6: 8

4/5: 16

3: 822

2: 1022

1: 34

Thick.

6

3

9

3

Total Sandstone = 114 ft.Total Shale = 85 ft.

199ft.Net Sandstone = 57%

OU Seismic Line

CSM Strat Test #61

6600’ 6620’ 6640’ 6660’ 6680’ 6700’ 6720’ 6740’ 6760’ 6780’6600’ 6620’ 6640’ 6660’ 6680’ 6700’ 6720’ 6740’ 6760’ 6780’

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Figure 3. (A) 3D spatial orientation of the 10 channel-fill sandstones. (B) Facies comprising each sandstone. Faciescolor code is provided in Table 1.

Erosional remnants

N

A

B

6600’ 6620’ 6640’ 6660’ 6680’ 6700’ 6720’ 6740’ 6760’ 6780’

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Figure 4. Depositional model for the Dad Sandstone Spine 1-2 area. Two sheet sandstones that outcrop there are shownas two yellow bars underlying the leveed-channel deposits. Figure modified from Mayall and Stewart (2000) andBeaubeouf (2004).

1km

Scales of heterogeneity Dimensions Applications to drilling

(I) Leveed-channel system 1-2km wide Channel complexes separated by levees; not connected.

(II) Leveed channel complex 0.5km wide; Channel sands not connected.50-70m thick

(III) Leveed-channel sand <0.5kwide Internal variability in facies 3-12m thick and reservoir quality.

70m

Sheets or splays

levees

Channel fillChannel fill

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Figure 5. (A) Channel-fill Sandstone #1 looking toward the northeast; downlap surfaces can clearly be seen. (B) Samesandstone looking west. C = ‘cutbank-like’ side of sandstone. P = ‘point bar-like’ side of sandstone. Red dashed line isestimated depth to base of the channel. Note the interpreted asymmetry of the channel-fill.

Downlap surfacesDownlap surfaces

~150 m

C

C

P

P

A

B

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Figure 6. Amplitude extraction map on interpreted horizon showing raised channel-fill due to differential compaction.Of particular importance here are the small slump scars which appear to be concentrated on the outside bends of sinu-ous channel. After Posamentier and Kolla (2003).

Raised channelRaised channel--fill is due to differential compactionfill is due to differential compaction

Small slump scarsSmall slump scars

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Figure 7. Spine 1 outcrop, looking south, showing six of the ten channel-fill sandstones. Channel-fill Sandstone #1 islabeled. The red rectangle shows the location and orientation of a ground-penetrating radar line which imaged thebase of Channel-fill Sandstone #1, and the position where it emerges at the ground surface (near shot-point 175). TheEMI horizon is horizontal, and images the bend in the channel sandstone toward the south, where the sandstoneemerges at the ground surface. Proximal levee beds occur in outcrop adjacent to the position of the channel-fill bend.

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Figure 8. (A) Ground penetrating radar line shot behind a channel-fill sandstone at Rattlesnake Ridge (B) which showsthe downlap of the channel base and the onlap of the channel-fill. (C) The contact zone shown in A. The red dashedarea is composed of thin-beds which are contorted and slumped toward the base of the channel. (D) Interfingers ofchannel-fill sandstone into the siltier slumped beds at the channel margin.

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Figure 9. (A) Conceptual diagram showing the asymmetric distribution of facies with respect to the inside and outsidebends of a channel. (B) The five major sub-environments associated with a leveed-channel system: E1) non-sinuous lev-eed-channel, E2) outside bend of sinuous channel, E3) inside bend of sinuous channel, E4) proximal levee, and E5) dis-tal levee. (after VanDyke, 2003).

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Figure 10. Schemitic illustration of a sinuous channel in plan view. The numerical value of sinuosity is determined as:thalweg length of a single bend wavelength (red arrow) / Axial length of a single bend wavelength (black arrow). Forexample, is red = 1036m (3399 ft) and blue is 764m (2507), then sinuosity = 1.36. Figure is modified from Keevil et al.(in press).

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Figure 11. Summary of channel geometry for Channel-fill Sandstone #1. Details are provided in the inset.

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Figure 14. Amalgamated Channel-fill Sandstones #4 and #5, showing the distribution of key facies. The red dashed linemarks the erosional surface which amalgamates the sandstones.

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801



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803



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Figure 20. Summary of channel geometry for Channel-fill Sandstones #9/10. Details are provided in the inset.

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Figure 21. Base of Channel-fill Sandstone #1 based upon shallow borehole drilling, electro-magnetic induction andground-penetrating radar surveys. Colors on the lower figure refer to the facies filling this portion of the channel(Table 1).

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Figure 22. (A) Hammer seismic acquisition. (B) CSM Strat Test #61 logs and resultant synthetic seismogram. Time-depth conversion is also shown. (C) Fully processed post-stack time-migrated seismic section recorded behind the out-crop across CSM Strat Test #61 well. The gamma-ray log and synthetic seismogram are superimposed at the properposition on the seismic line.

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Figure 23. Graphical illustration of Terrain and Elevation Corrections. Various elevations are shown, from which thecalculations were made.

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Figure 24. Seismic line showing the projection of the master channel (orange dashed line) and each of the channel-fill

sandstones that are predicted to cross the line. Positions of the channel-fills are based upon the projections shown in

Figures 11-13 and 15-20. Yellow is Channel-fill Sandstone #1; Dark blue = Channel-fill Sandstone #2; Gray-blue =

Channel-fill Sandstone #4; Red = Channel-fill Sandstone #5; Lime green = Channel-fill Sandstone #6; Brown = Chan-

nel-fill Sandstones #9/10. Dashed turquoise line represents an unidentified channel with faint reflections downlapping

onto the base (red arrows). A set of downlapping reflections (red arrows) are apparent beneath the master channel to

the north of the CSM Strat Test #61 well.

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Figure 25. (A) Separate channel-fills interpreted from a sinuous bend in a subsurface channel (B and C). The channel-fills are vertically separated based upon the seismic interpretation. After Kolla et al (2001).

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Figure 26. Plan view of the interpreted sinuosity of the 10 channel-fill sandstones shown in Figures 11-13 and 15-20.The position of the CSM Strat Test #61 well is shown by the white circle. Color scheme for each channel-fill (CF) is pro-vided.

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Figure 27. 3D inclined perspective of the 10 channel-fill sandstones shown in Figure 26. The position of the CSM StratTest #61 well is shown.