Variability in Wave-Dominated Estuary Sandstones: Implications on Subsurface Reservoir Development

BULLETIN OF CANADIAN PETROLEUM GEOLOGY VOL. 50, NO. 1 (MARCH, 2002), P. 118-137

Variability in wave-dominated estuary sandstones: implications on subsurface reservoir development

S.M. HUBBARD1 M.K. GINGRAS Shell Canada Limited Department of Geology 400 - 4 Avenue SW University of New Brunswick Calgary, AB T2P 2H5 Fredericton, NB E3B 5A3

S.G. PEMBERTON M.B. THOMAS Ichnology Research Group Shell Canada Limited Department of Earth and Atmospheric Sciences 400 - 4 Avenue SW University of Alberta Calgary, AB T2P 2H5 Edmonton, AB T6G 2E3

ABSTRACT

Although ancient estuarine deposits are generally characterized by complex facies distributions, their associated sand- stones commonly constitute prolific hydrocarbon reservoirs. Ebb-tidal delta, barrier-bar, tidal-inlet, flood-tidal delta, tidal- channel, tidal-flat and bayhead delta sub-environments can all be associated with sandstones that may potentially have excellent reservoir properties. Distinguishing between depositionally distinctive sandstones is crucial to the accurate reserve and deliverability assessment of reservoirs within estuarine systems. This knowledge can help plan an optimum development strategy for a hydrocarbon play. In this study, the quality and distribution of sandstones from wave-dominated estuaries is compared using subsurface data from the Lower Cretaceous Bluesky Formation of the Peace River area in Alberta. Modern sediments from Willapa Bay, Washington, are used to support observations made in the Bluesky Formation, and fill in information gaps inherent with subsurface datasets. The modern and fossil estuarine systems studied show that tidal-inlet and barrier-bar sandstones are characterized by the best reservoir qualities, followed by tidal delta, bayhead delta, tidal-channel, and lastly tidal-flat sandstones. Variability in preservation potential amongst ancient estuarine complexes can be significant however, and is an important factor with respect to recognizing, evaluating, and ranking the economic importance of individual units from any given estuarine deposit.

RÉSUMÉ

Malgré que les dépôts estuariens anciens soient généralement caractérisés par des distributions de faciès complexes, les grès associés sont communément constitués de réservoirs prolifiques d’hydrocarbures. Les sous-environnements de reflux de marée, de barrière littorale, de passe de marée, de delta d’inondation de marée, de chenal de marée, d’estran et de delta de fond de baie peuvent tous être associés avec des grès qui pourraient potentiellement avoir d’excellentes propriétés de réservoir. Faire la distinction entre ces grès de dépôts distincts est crucial pour l’évaluation de réserves précises et de la productivité des réservoirs à l’intérieur des systèmes estuariens. Cette connaissance peut aider à planifier une stratégie optimum de développement pour une cible d’exploration des hydrocarbures. Dans cette étude, la qualité et la distribution des divers grès situés dans des estuaires à dominance de vagues sont comparés avec les données de subsurface provenant de la Formation de Bluesky du Crétacé inférieur de la région de Peace River en Alberta. Les sédiments modernes de la baie de Willapa, Washington, sont utilisés pour supporter les

1 Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, U.S.A.

118 VARIABILITY IN WAVE-DOMINATED ESTUARY RESERVOIRS 119

observations faites dans la Formation de Bluesky, et permettent de combler les lacunes d’information inhérentes aux jeux de données de subsurface. Les systèmes estuariens modernes et fossiles étudiés montrent que les grès de passe de marée et de barrière littorale sont caractérisés par les meilleures qualités de réservoir, suivis par ceux de delta de marée, de delta de fond de baie, de chenal de marée et en dernier par les grès d’estran. Toutefois, la variabilité du potentiel de préservation parmi les complexes estuariens anciens peut être significative, et est donc un facteur important pour d’abord reconnaître, puis évaluer et mettre en ordre l’importance économique des unités individuelles de tout type donné de dépôt estuarien.

Traduit par Lynn Gagnon

INTRODUCTION preserved ancient deposit is desirable, preferably one that comprises many genetically different sandstones. This paper focuses on a common seaward termination of a fluvial system — the estuary. Although estuarine deposits are ANCIENT DEPOSITS: STUDY AREA AND DATABASE characteristically variable, a common trait is that they contain The database considered in this study is taken from the hydrocarbons in the subsurface (e.g. Reinson et al., 1988; Lower Cretaceous Bluesky Formation in the north-central Barwis, 1990; Howard and Whitaker, 1990; Dyson, 1998). In Alberta subsurface (Fig. 1; Table 1). The Bluesky Formation in this study, ancient and modern databases are used to assess this area was deposited in a large, wave-dominated estuary and the reservoir quality/potential of various sand bodies from is known to contain a significant proportion of the billions of wave-dominated estuaries. Common sub-environments that are barrels of bitumen that comprise the Peace River Oil Sands characterized by sandy, potentially reservoir quality deposits deposit (Hubbard et al., 1999). This extensive heavy oil field include tidal inlet, ebb- and flood-tidal deltas, barrier bar, tidal is currently being developed in Township 85 Range 18W5, channel, tidal flat and bayhead delta. The thickness, distribu- where fluvial-deltaic strata of the underlying Ostracode Zone tion, geometry, and reservoir properties of individual deposits also contain vast reserves of bitumen (Hubbard et al., 1999; are discussed. 2001). The subsurface dataset includes wireline logs from The understanding of ancient estuarine deposits and their approximately 250 wells, 81 of which have core that penetrate hydrocarbon potential has been significantly advanced through the study interval. Reservoir facies are interpreted to include the development of incised valley/estuarine facies models (Roy bayhead delta, tidal-flat, tidal-channel, flood- and ebb-tidal et al., 1980; Clifton, 1982; Roy, 1984; Frey and Howard, 1986; delta, tidal-inlet, and barrier/shoreface deposits. The fossil Boyd et al., 1992; Dalrymple et al., 1992; Reinson, 1992). The estuary in the Bluesky Formation is somewhat exceptional in premise of this study is to provide a relatively simple descrip- that it aggraded over time; a complicated history of fluvial and tion of a series of common estuarine sedimentary deposits for estuarine incision appears to be absent. As a result, units potential application in industry. It is not meant to challenge the deposited in individual estuarine sub-environments across the existing estuarine sedimentological paradigms, but rather to study area are both recognizable and mappable (Fig. 2). demonstrate the application of those models while focusing on The economic potential of many units in the Bluesky the subsurface mapping of hydrocarbon reservoirs. The study Formation is significantly influenced by the presence of water demonstrates that, through estuarine facies identification and zones, especially toward the southern and westernmost edges mapping, a better understanding of reservoir distribution is of the study area. Because this study is not intended to be a case attainable and an effective hydrocarbon development strategy example of the Bluesky Formation reservoir, fluid saturation can be applied. values for each of the different sandstones in the field are not compared. Instead, we focus on a selection of rock/reservoir BACKGROUND AND METHODOLOGY properties and consider all the potential reservoir facies, to offer broader application. Porosity values are primarily from The preservation potential of estuarine deposits is extremely core measurements, supplemented by values derived from variable and normally examples in the rock record are domi- wireline logs. Gamma-ray logs, supplemented by qualitative nated by a limited number of facies. Examples include the estimates during core examination, provide estimates of the Pleistocene succession at Willapa Bay, Washington (predomi- sand/shale ratio in each deposit. The relative abundance of nantly point-bar, tidal-flat and shallow bay facies – Clifton, shale interbeds was also derived qualitatively from core 1983; Gingras et al., 1999), the Cretaceous McMurray observations. Isopach maps, using the constraints of a wave- Formation of Alberta (predominantly point-bar and tidal-chan- dominated-estuary model, delineate the areal distribution and nel deposits – Wightman and Pemberton, 1997; Ranger and geometries of reservoir sandstones. Gingras, 2001), and the Cretaceous Glauconitic Sandstone of Alberta (predominantly point-bar, bay and bayhead delta MODERN DEPOSITS: STUDY AREA AND DATABASE deposits – Broger et al., 1997). To make a legitimate com- The modern database employed in this study is Willapa Bay, parison of various estuarine sandstones, an exceptionally well Washington (Fig. 3). The dataset used is derived from field 120 S.M. HUBBARD, M.K.. GINGRAS, S.G. PEMBERTON, AND M.B. THOMAS

Fig. 1. A, B) Regional study area and paleogeographic framework for the Bluesky Formation in north- central Alberta (modified from Hubbard et al., 1999). C) Well and core control in the study area. observations and recent reports pertaining to this estuary Estuarine sedimentation is characteristically variable (Clifton et al., 1989; Gingras, 1999; Smith et al., 1999). Data (Howard and Frey, 1973; Clifton, 1982; Boyd and Penland, includes textural trends, unit thicknesses, internal hetero- 1984), and hence, no two estuaries are exactly alike. Willapa geneities, and the areal extent of sand bodies. Inferences Bay, although useful as an analog to the Bluesky Formation, drawn from Willapa Bay are predominantly used to bolster has many inherent differences from the subsurface deposit interpretations of the Bluesky Formation, and refine them (Hubbard, 1999; Hubbard et al., 2000). A summary of the main where information from the subsurface is limited by poor core controls on deposition for the Bluesky Formation and Willapa or well control. Sands from Willapa Bay comprise tidal-flat, Bay is presented in Table 2 in order to outline some of the tidal-channel, tidal-inlet and barrier-spit deposits. more obvious differences between the two estuarine systems. VARIABILITY IN WAVE-DOMINATED ESTUARY RESERVOIRS 121

Table 1. Subsurface Lower Cretaceous stratigraphy of the northwest plains, Alberta.

Some of the major differences are related to depositional realm and coastal configuration, tectonic regime, and sediment sources. Despite these differences, common sedimentological and stratigraphic elements link the two deposits, as demon- Fig. 2. A) Schematic diagram of the wave-dominated estuary strated herein. facies model interpreted for the Bluesky Formation in the study area. Lines A–A′, B–B′ and C–C′ reflect locations of cross-sections pre- sented in Figures 5 and 9. B) Gross sand map of the Bluesky Formation. C) Areal extent of the estuarine sandstone reservoirs in the ESTUARINE SANDSTONES Bluesky Formation.

BLUESKY FORMATION sand, for the purpose of this study, includes bitumen-saturated Hubbard et al. (1999) interpreted the Bluesky Formation at sandstone, water-saturated sandstone, interbedded sandstone Peace River as a wave-dominated estuary; a modified version and mudstone where sandstone is the predominant component, of this model is presented in this paper (Fig. 2A). Gross sand and muddy or silty sandstone. distribution within the Bluesky Formation was particularly Table 3 describes the individual reservoir facies in the influential in arriving at this interpretation (Fig. 2B). Gross Bluesky Formation. Figure 2C summarizes the areal distribu- 122 S.M. HUBBARD, M.K.. GINGRAS, S.G. PEMBERTON, AND M.B. THOMAS tion of each of the main facies in the subsurface. These were 60 km south of Willapa Bay. The sand is transported northward determined using the 10 m gross sand contour (Fig. 2B) to by longshore currents. Tides then bring the sediment through delineate the outer boundary of each deposit. The areas of tidal- the inlet at the north end of the estuary (Figure 3; Luepke and channel and tidal-flat deposits were not calculated, because Clifton, 1983). Fluvial input into the bay is limited to the dis- associated sandstone units are typically <10 m thick. Individual charge of 5 small rivers that originate on the northern and east- reservoir deposits are defined on the basis of sedimentary tex- ern sides of the Willapa Hills watershed. Fluvially derived ture, sedimentary structure, geographical position, and overall sands are present in the uppermost, landward reaches of the geometry. estuary in river-dominated channels (Luepke and Clifton, 1983). Table 4 summarizes some of the sedimentary character- WILLAPA BAY, WASHINGTON istics of various sandy deposits at Willapa Bay. As an analogous system to the Bluesky Formation, Willapa Bay (Figure 3) is significantly influenced by both waves and FACIES DESCRIPTIONS tides. Most of the sand in the bay is derived from the Columbia Prior to discussing the sandstone deposits from the various River, which discharges into the Pacific Ocean approximately estuarine sub-environments of the Bluesky Formation and

Fig. 3. Location map of Willapa Bay, Washington. A) Landsat image of the estuary. The arrows refer to photographs presented in the paper. The labels represent the figure numbers where the photographs are located. The arrows labelled 10D and 11D point in the view direction of those photographs; the arrows labelled 4D, 7D and 8D point to the areal outline of photographs and diagrams. B) Sediment texture of modern deposits in the bay (modified from Clifton, 1983). Inset map shows the location of Willapa Bay in southwestern Washington. VARIABILITY IN WAVE-DOMINATED ESTUARY RESERVOIRS 123

Table 2. Depositional controls that influence(d) sediment accumulation and preservation in the Bluesky Formation and at Willapa Bay. The controls result in differences in the nature, type, and quantity of facies and facies associations preserved.

Table 3. Sedimentological characteristics of reservoir facies from the Bluesky Formation at Peace River. HWB = heterolithic wavy bedding; IHS = inclined heterolithic stratification. 124 S.M. HUBBARD, M.K.. GINGRAS, S.G. PEMBERTON, AND M.B. THOMAS

Table 4. Sedimentological characteristics of sandy facies from Willapa Bay, Washington. (Note*: Tidal inlet/delta deposits are analyzed from Pleistocene outcrop at the northern edge of the current bay-mouth at Willapa Bay; these sediments are interpreted to have been deposited in an analogous setting to those of the modern bay: see Clifton et al., 1989 for further discussion).

Willapa Bay, clarification of the term tidal channel as it is progradational ebb-tidal delta deposits interfinger with used in the context of this paper is necessary. Tidal channels marine mudstones (Fig. 5A). are present throughout wave-dominated and mixed (wave- Ebb-tidal delta deposits of the Bluesky Formation at Peace and tide-influenced) estuaries; however, their importance as River encompass approximately 44 sections, or 1.1 x 108 m2 reservoirs is more or less limited to bay mouth facies associ- (Fig. 2). Where their average gross thickness is 15.5 m (Table ations (tidal inlets and tidal deltas) in wave-dominated 3), sandstones up to 20 m thick accumulated in inferred ebb- estuaries (Roy et al., 1994). As tidal channels translate into tidal channels proximal to the fossil tidal inlet (Fig. 2B). the inner estuary they commonly become increasingly het- Comparison with deposits at Willapa Bay is speculative, erolithic or muddy (Smith, 1989; Gingras et al., 1999). In this because the ebb-tidal delta deposits are largely inaccessible. study, economically significant tidal channels are grouped However, the ebb-tidal delta platform extends up to 4 km into with genetically similar deposits; for example, tidal channels the Pacific Ocean (Fig. 4D; Clifton et al., 1989). dominated by flood-tidal currents on the bayward side of the barrier/inlet complex are considered as flood-tidal Barrier delta deposits. Where tidal channels are specifically focused The barrier in the Bluesky Formation is composed of well on in the paper, they are 1) composed of reservoir quality sorted, very fine- to fine-grained sandstones deposited in a sediments, and 2) distinguishable from other sandy estuarine shoreface to shelfal/offshore environment (Table 3). The aver- units within the data available. age porosity of the sandstones is 26.6%, and the average gamma-radioactivity 43.5 API units (Fig. 6C). The succession Ebb-Tidal Delta systematically coarsens upward, and the reservoir quality Sandstones interpreted to have been deposited on an ebb- increases upwards as a result (Fig. 6C). Mud-lined burrows are tidal delta in the Bluesky Formation are moderately well moderately abundant; however, bioturbation is rare overall (Fig. sorted, fine grained and have average porosities of 24.5%. 6B). Mud laminae, coaly debris and pebbly horizons occur in Gamma-radioactivity measures 52.5 API units on average, rare to moderate abundance (Fig. 6A). Low- to high-angle and shale interbeds are moderately abundant to rare (Fig. 4). cross-stratification is common (Fig. 6A). Sandstone quality Wood fragments and coaly debris are moderately abundant, varies along the length of the barrier, with the thickest, most and sand-dominated heterolithic wavy bedding is characteris- continuous sand present in the northern part of Township 83 tic (Fig. 4A, B). Bioturbation is typically rare to moderate Range 19W5. Variability within the deposit is difficult to char- (Table 3). The lithology of the ebb-tidal delta changes sys- acterize due to poor core control. Deposits are gradational with tematically, and mud laminae and biogenic reworking tidal-inlet sandstones northward, and central estuary mudstones increase notably towards the distal, western edge of the and sandstones to the east (Fig. 5B). They are disconformably deposit. The best reservoir sandstones are adjacent to the overlain by distal, shelfal-offshore sandstones and siltstones to gradational boundary with tidal-inlet facies. To the west, the west (Hubbard et al., 1999). VARIABILITY IN WAVE-DOMINATED ESTUARY RESERVOIRS 125

Fig. 4. Ebb-tidal delta deposits. A, B) Sandstone with wavy mud interbeds in the Bluesky Formation (A: 4-34-85-19W5, 536.0 m; B: 4-15-85-19W5, 548.2 m). The arrow points to a small burrow within the mud laminae. C) Typical geophysical well-log profile through ebb-tidal delta deposits in the Bluesky Formation (4-29-85-19W5). The core interval is indicated by the black rectangle. D) Magnified landsat image of the ebb-tidal delta breaker zone and tidal inlet at Willapa Bay (refer to Fig. 3 for location).

The sand body in the Bluesky Formation is up to 8 km wide, Tidal Inlet and greater than 23 km long (Fig. 2A). Due to a paucity of wells south of the study area, the actual length of the barrier is Tidal-inlet deposits in the Bluesky Formation consist of well unknown. The area of the sand body includes more than 113 sorted, upper fine-grained sandstones (Table 3). The average sections (Fig. 2C). Deposits typically average 17 m in thick- porosity of associated units is approximately 28%, ranging up ness, but are > 20 m in some localities (Fig. 2B; Table 3). These to 32% locally (Fig. 7C). The radioactivity of inlet deposits dimensions are comparable with North Beach Peninsula at averages 42.0 API units. A characteristic feature of tidal-inlet Willapa Bay, which is 38 km in length, and has a subaerially deposits in the Bluesky Formation is planar-parallel to low- exposed width of 3.5 km (Fig. 3). The total width of the sand angle crossbedding (Fig. 7A, B), and little internal variability. body at Willapa Bay including the seaward, subtidal shoreface Tidal bundles and reactivation surfaces are present locally (Fig. sands is considerable, extending many kilometres offshore (Ed 7A; Hubbard, 1999). Evidence of biogenic reworking is absent. Clifton, pers. comm., 2001). The maximum thickness of the Shale laminae are generally absent within the central part of the modern barrier is greater than 25 m, comprised of lower inlet. Tidal-inlet deposits grade laterally into barrier-bar sand- shoreface (10–16 m), upper shoreface (about 9 m), and eolian stones to the south, and tidal delta sandstones to the east and sands (<2 m) (Smith et al., 1999). west (Fig. 5). 126 S.M. HUBBARD, M.K.. GINGRAS, S.G. PEMBERTON, AND M.B. THOMAS

Tidal-inlet deposits of the Bluesky Formation occur in an averages 14.4 m, with a maximum of 22 m (Fig. 2B; Table 3). area approximately 7.2 km by 6.7 km (19 sections; Fig. 2C). Analogous deposits at Willapa Bay are largely absent owing to The sedimentary package averages 15.8 m in thickness, with a the geometry of the bay whereby a large channel system nor- maximum measured thickness of 23 m (Fig. 2B; Table 3). Due mal to the inlet prevents development of a flood-tidal delta (Fig to a lack of internal heterogeneity within associated facies, 2A; Clifton et al., 1989). As the bay fills, however, the com- the net-to-gross ratio of tidal-inlet sands is typically one. At posite sand body generated by these flood-tidal-dominated Willapa Bay, the inlet is approximately 7 km by 9 km in area channels is comparable in size and geometry to the interpreted and associated channels can exceed 30 m in depth (Figs. 3 and flood-tidal delta deposits in the Bluesky Formation (Figs. 3, 7D; Smith et al., 1999). 8D). Measuring from the southern limit of the tidal inlet at Willapa Bay to the distal end of the sand deposits, the area of Flood-Tidal Delta the sedimentary package being produced is 209 km2: the flood Moderately well sorted, upper fine-grained sandstones are tidal complex present in the Bluesky Formation covers an area 2 characteristic of flood-tidal delta deposits in the Bluesky of approximately 176 km . The depth of the flood-tidal chan- Formation. The porosity of the deposit averages 27%, with nels at Willapa Bay average 10 to 20 m (Clifton and Phillips, gamma-ray values of 49.8 API units (Fig. 8C). Low-angle to pla- 1980), sufficient to generate a flood-tidal delta sand package as nar-parallel bedding is pervasive, with inclined heterolithic strat- thick as that in the Bluesky Formation. ification present in some cores (Fig. 8A, B). Wood fragments and coaly debris are present in rare to moderate abundance. Tidal Channel Bioturbation is rare overall; however, it increases towards the Tidal-channel deposits in the Bluesky Formation units are edges of the delta. Mud laminations also increase in abundance rare overall. They consist predominantly of point-bar deposits towards the edges of the deposit; however, overall, the laminae composed of well sorted, fine-grained sandstones commonly are rarely to moderately abundant within associated facies. The interbedded with thin mud laminae (Fig. 10A; Table 3). The area characterized by the best reservoir quality sandstones occurs dominant characteristic is inclined heterolithic stratification in the northwestern part of Township 84 Range 17W5, proximal (IHS) where mud laminae are common, and low- to high-angle to the tidal inlet (Fig. 2). Flood-tidal delta deposits overlap cen- crossbedding where mudstones are absent. Trough crossbed- tral estuarine mudstones and sandstones to the east, and are inter- ding is also present locally (Fig. 10B). The average porosity of preted to grade into tidal-inlet deposits to the west (Fig. 9). associated units is 24.4% and shaliness, as measured from Flood-tidal delta sands in the Bluesky Formation extend gamma-ray logs, averages almost 54 API units (Fig. 10C). over nearly 70 sections (Fig. 2A, C). The gross sand thickness Bioturbation is rare to moderately abundant, mostly associated

Fig. 5. Stratigraphic cross-sections through lower estuary deposits in the Bluesky Formation. The top of the Bluesky Formation is used as the datum. A–A′ shows progradation of ebb-tidal delta deposits to the west whereas B–B′ shows the gradational relationship between tidal inlet and barrier-bar sandstones (refer to Fig. 2A for location). Note the relatively “clean” log character through thick tidal-inlet sequences in wells 8-17-85-18W5 (A–A′) and 7-9-85-18W5 (B–B′). Gamma-ray logs are shown. Core intervals are indicated by the black rectangles. Fr a more comprehensive analysis of the Lower Cretaceous stratigraphy in the Peace River area, see Hubbard et al. (1999). VARIABILITY IN WAVE-DOMINATED ESTUARY RESERVOIRS 127 with the mudstone laminae. Chert pebble lags and bioclastic 300 to 600 m wide and 6 to 15 m deep at low low tide (Clifton debris are rare to moderate. Tidal-channel reservoirs in the and Phillips, 1980), are most comparable with tidal channels Bluesky Formation are highly variable and unpredictable, interpreted in the Bluesky Formation (Fig. 10D). related to numerous facies of the middle to upper estuary including those deposited on tidal flats, in quiescent embay- Tidal Flat ments and on the distal flood-tidal delta. Sandy tidal-flat deposits in the Bluesky Formation are fine Tidal-channel trends in the Bluesky Formation are difficult grained and moderately well sorted, with an average porosity to map. Individual channel deposits are typically up to 7 m of 24%. Sandstones are typically muddy, as reflected by the rel- thick, although stacked tidal-channel sands attain thicknesses atively higher average gamma-radioactivity of 56.3 API units of 15 m (Table 3). At Willapa Bay, tidal channels are the dom- (Fig. 11C). Mud laminae, shelly debris, coal fragments, and inant morphological features present in the estuary. organic detritus are rarely present (Table 3). Primary physical Meandering channels in the middle to upper estuary, typically structures are absent, due to the reworking of sediment by ben- thic organisms; a diagnostic feature of the sandstones is a bur- row-mottled texture (Fig. 11A, B). Lateral variability within individual tidal flat units is difficult to assess, because facies cannot be correlated between wells. Tidal flat sandstones are associated typically with tidal-channel deposits of the middle to upper estuary in the Bluesky Formation. Individual tidal flat deposits in the Bluesky Formation are less than 2 m thick (Table 3). Modern tidal flat deposits at Willapa Bay extend up to 1500 m laterally (Fig. 11D), and are postulated to be up to 3 m in thickness based on the tidal range of 2 to 3 m.

Bayhead Delta Very fine- to fine-grained sandstones are characteristic of bayhead delta deposits in the Bluesky Formation (Table 3). Deposits range from poorly to well sorted, with 26.5% poros- ity on average. Density-porosity logs demonstrate an overall upward increase in reservoir quality, typical of deltaic deposits (Fig. 12C). Shale interbeds are rarely to moderately present, with the gamma-ray averaging 51 API units (Fig. 12C). Sedimentary structures, including current ripples and crossbed- ding are common, and bioturbation is rare to absent (Fig. 12A, B). Coaly debris and laminae are present in moderate abun- dance. Lateral variability across associated deposits is moder- ate to high. Bayhead delta deposits, restricted to the southeastern corner of the study area (Fig. 2A), prograde onto central estuary mudstones, and are commonly interbedded with units associated with tidal flat deposition (Fig. 9). In the Bluesky Formation, bayhead delta sandstones averag- ing 12.1 m in thickness cover an area extending greater than 38 sections (Fig. 2; Table 3). Bayhead delta deposits at Willapa Bay are restricted to the narrow river channels landward of the bay. Coarse-grained sediment is located only in the upper extremes of the rivers, and, therefore, is incomparable to the relatively vast bayhead delta deposits in the Bluesky Formation. Fluvial currents and resultant sediment input into Willapa Bay is much less dominant than that originating from Fig. 6. Barrier-bar deposits. Pebbly horizon (A) and mud-lined tides (Clifton et al., 1989). In contrast, the Cretaceous estuary burrows (B) in Bluesky Formation sandstones (A: 5-33-83-19W5, 597.4 m; B: 14-11-83-20W5, 598.6 m). C) Typical geophysical well-log that deposited the Bluesky Formation in the study area had tidal profile through barrier-bar deposits in the Bluesky Formation (5-33-83- and fluvial sources of comparable current energy, resulting in 19W5). Note that porosity increases upwards, through the reservoir the obvious tripartite sediment texture variation interval. The core interval is indicated by the black rectangle. Refer to Figure 3 for location and areal distribution of the modern barrier spit (sand–mud–sand) across the estuary (see Fig. 4 from at Willapa Bay. Dalrymple et al., 1992). 128 S.M. HUBBARD, M.K.. GINGRAS, S.G. PEMBERTON, AND M.B. THOMAS

Fig. 7. Tidal-inlet deposits. Physical sedimentary structures include reactivation surfaces (A) and planar-parallel bedding (B) in Bluesky Formation sandstones (A: 3-10-85-18W5, 580.4 m); B: 14-21- 85-18W5, 562.0 m). C) Typical geophysical well-log profile through tidal-inlet deposits in the Bluesky Formation (5-20-85-18W5). The core interval is indicated by the black rectangle. D) Areal extent and bathymetry of the tidal inlet at Willapa Bay (Clifton et al., 1989; refer to Fig. 3 for location).

DISCUSSION Estuarine sandstones in the Bluesky Formation are largely unconsolidated as a result of early oil migration into the reser- A summary of results from core and well-log analysis of voir which reduced the effects of later diagenetic processes the various estuarine reservoir facies of the Bluesky (Hubbard, 1999). The data collected suggests that variability Formation is presented in Figure 13A. In general, the reser- between measured values, such as porosity and shaliness is not voir potential of a sedimentary unit depends fundamentally on extreme amongst the different reservoir sandstones (Fig. 13). the following: 1) a minor porosity, shaliness, and reservoir When these values are compared, however, a distinctive trend homogeneity (Fig. 13B); and, 2) size, thickness, and pre- is evident, whereby reservoir quality is highest in sandstones dictability (Fig. 13C) of the reservoir units. From a reservoir associated with the tidal inlet, and degrade in both seaward development strategy point of view, understanding the quality and landward directions (with the exception of bayhead delta and distribution of deposits present in the various deposi- deposits) (Fig. 13B). These observations are consistent with tional environments can help optimize hydrocarbon extrac- those of Zaitlin and Shultz (1990) and Peijs-van Hilten et al. tion over the duration of the capital-intensive project. (1998) from other subsurface estuarine deposits of western VARIABILITY IN WAVE-DOMINATED ESTUARY RESERVOIRS 129 atum. Core ) Magnified landsat image of sandy, flood tidally ) Magnified landsat image of sandy, D ) in Bluesky Formation sandstones (A: 3-20-84-17W5, 611.4 m; B: 4-5-85-17W5, ) in Bluesky Formation sandstones (A: 3-20-84-17W5, 611.4 B ) and crossbedding ( A Stratigraphic cross-section through middle to upper estuary deposits in the Bluesky Formation, demonstrating interpreted Fig. 9. intervals are indicated by the black rectangles (refer to Fig. 2A for location). progradational nature of both flood-tidal delta and bayhead delta sandstones. The top of the Bluesky Formation is used as d progradational nature of both flood-tidal delta and bayhead sandstones. ) Typical geophysical well-log profile through flood-tidal delta deposits in the Bluesky Formation (11-28-84-17W5). geophysical well-log profile through flood-tidal delta deposits in the Bluesky Formation (11-28-84-17W5). Typical ) Flood-tidal delta deposits. Inclined heterolithic stratification ( C Fig. 8. dominated channels in Willapa Bay (refer to Fig. 3 for location). 602.4 m). 130 S.M. HUBBARD, M.K.. GINGRAS, S.G. PEMBERTON, AND M.B. THOMAS

Fig. 10. Tidal-channel deposits. Inclined heterolithic stratification (A) and trough crossbedding (B) in the Bluesky Formation (A: 7-30-83-15W5, 648.7 m; B: 7-9-84-16W5, 648.5 m). C) Typical geophysical well-log profile through a sandy tidal-channel sequence in the Bluesky Formation (11-17-83-17W5). D) Air photo of a tidal channel, and associated tidal channels and run-off creeks in Willapa Bay (refer to Fig. 3 for location).

Canada. The fossil estuary preserved in the Bluesky high porosity (28% average) and contain little fine-grained Formation is sand dominated, and, in muddier estuarine sys- material. The importance of these sediments is somewhat miti- tems, this trend may be more sharply delineated. Limitations gated because of their limited areal extent; however, with an in wireline-log measurements must also be considered; for average pay thickness of 15.8 m, they provide one of the most example, gamma-ray log values give average shaliness across attractive development targets (Fig. 13C). The estimated BIP in an interval, and cannot distinguish whether a unit is a biotur- the tidal-inlet deposits of the Bluesky Formation is just over bated muddy sandstone or a sandstone with common, thin one billion barrels (Fig. 13A). mud interbeds. Therefore, qualitative core observations are an The preservation potential of tidal-inlet deposits is consid- important component in assessing the hydrocarbon potential. ered to be high (Hoyt and Henry, 1967; Tye and Moslow, The resource potential is estimated for each estuarine suben- 1992). The recognition of numerous documented examples vironment in the Bluesky Formation (Fig. 13A, last column). support this statement (subsurface examples: Lower Mannville The hydrocarbon present in the subsurface at Peace River is – Zaitlin and Shultz, 1990; Triassic Halfway Formation – heavy oil (API <10). The bitumen in-place (BIP) is estimated Willis and Moslow, 1994a) (outcrop examples: Horseshoe by multiplying the area, average thickness, and porosity of each Canyon Formation at Drumheller, Alberta – Saunders, 1989; estuarine sandstone by a bitumen saturation of 80%. Milk River Formation in southern Alberta – Cheel and Leckie, 1990). This excellent preservation potential adds to the attrac- TIDAL-INLET RESERVOIRS tiveness of tidal-inlet deposits as reservoir targets, as does their propensity to be overlain regionally by marine shale and mud The highest quality reservoir was clearly formed in a tidal seals (Allen and Posamentier, 1994). inlet (Fig. 13B). These relatively homogeneous sands have a VARIABILITY IN WAVE-DOMINATED ESTUARY RESERVOIRS 131

Fig. 11. Tidal-flat deposits. A, B) Burrow-mottled sandstones in the Bluesky Formation (A: 4-24-84- 16W5, 633.1 m; B: 6-25-83-15W5, 628.5 m). The arrow points to a coalified root. C) Typical geophysical well-log profiles through tidal flat deposits (highlighted) in the Bluesky Formation (6-25-83-15W5 and 11-17-83-17W5). The core intervals are indicated by the black rectangles. D) Air photo of an extensive tidal flat in Willapa Bay (refer to Fig. 3 for location).

BARRIER-BAR RESERVOIRS logical features (Fig. 3). However, although Pleistocene bay The Bluesky Formation and Willapa Bay case studies indi- sediments are common in the area, very few represent earlier, cate that barrier-bar deposits are characterized by good reservoir Pleistocene barriers. However, in the final phase of bay infill- quality and tremendous lateral extent. The average porosity of ing, a fossil barrier is more commonly preserved (the terminal the deposits is excellent (26.6%), although sediments are some- barrier). This is supported by several subsurface studies (e.g. what heterogeneous, with mud laminae common locally Chiang, 1984; Willis and Moslow, 1994b), and is reflected in (Fig. 13A, B). However, these deposits are extensive (about the widely accepted tripartite wave-dominated estuary facies 113 sections) and potentially thick (up to 25 m) (Fig. 13C). model (Dalrymple et al., 1992). Notably, this facies association Furthermore, during stillstand and highstand, barrier bars are is not recognized in Neogene shelf-margin estuaries of the typically restricted geographically due to a close association Celtic Sea (Reynauld et al., 1999). In these (wave-dominated) with the bay mouth environment, and, therefore, are quite pre- estuaries, tidal-inlet deposits are most commonly preserved dictable (Roy et al., 1994). The BIP is a staggering 6.5 billion near the bay mouth. barrels if an 80% bitumen saturation is assumed (Fig. 13A). TIDAL DELTA RESERVOIRS Numerous changes in relative sea level may eradicate estu- arine barrier-bar deposits. For example, the modern barrier at Flood-tidal delta sands are characterized by high porosity Willapa Bay is among the bay’s most prominent geomorpho- (27%) and relatively thick pay (14.4 m) (Fig. 13B, C). The 132 S.M. HUBBARD, M.K.. GINGRAS, S.G. PEMBERTON, AND M.B. THOMAS

Fig. 12. Bayhead delta deposits. Crossbedding (A) and ripples (B) in sandstones of the Bluesky Formation (A: 6-25-83-15W5, 615.8 m; B: 6-25-83-15W5, 620.9 m). C) Typical geophysical well-log pro- file through bayhead delta deposits in the Bluesky Formation (6-25-83-15W5). Note that porosity increases upwards, through the reservoir interval. The core interval is indicated by the black rectangle. D) Facies distribution in a modern bayhead delta, Upper Hawkesbury River, Australia (modified from Nichol et al., 1997). Land is to the west.

sands are clean in the central part of the deposit, but are pro- delta sediments in the Bluesky Formation and in other ancient gressively muddier towards the bayward margins. The flood- deposits (e.g. Yang and Nio, 1989; Willis and Moslow, 1994a), tidal delta encompasses a large lateral area, and is relatively indicates that their potential should not be discounted. This is predictable. Elsewhere, this depositional environment invari- especially evident at Peace River, where 2.2 billion barrels ably represents a large component of the reservoir quality sands (BIP) is estimated for these deposits in the Bluesky Formation of a wave-dominated estuary deposit (Roy et al., 1980; Boyd (Fig. 13A). and Honig, 1992). Flood-tidal delta sandstones in the Bluesky Formation contain approximately 3.5 billion barrels of bitu- BAYHEAD DELTA RESERVOIRS men, based on an 80% bitumen saturation value (Fig. 13A). Compared to lower estuary sandstones (tidal inlet, tidal The location of the flood-tidal delta inside the estuary deltas and barrier bar), bayhead delta deposits are considered to increases its preservation potential and, thus, associated units have less economic importance, based on observations from the are known to be prolific reservoirs (e.g. Barwis, 1990; Zaitlin Bluesky Formation and Willapa Bay. The quality of resource in and Shultz, 1990). Where present, flood-tidal delta deposits such accumulations can be reduced by the presence of mud, should be central to any wave-dominated estuary exploitation lower overall sorting, and less average pay thickness (Fig. 13). strategy because they are commonly well preserved, demon- Nichol et al. (1994) noted that, where estuaries undergo filling strate good resource quality, and can potentially provide high during continual relative transgression with a dominant marine resource volumes. Ebb-tidal delta deposits can have similar sediment source, bayhead delta deposits are often underdevel- reservoir quality (Sexton and Hayes, 1996), but their preserva- oped. In many cases, sediments are often laterally heteroge- tion potential is low because they are often reworked into neous, with zones of reservoir quality sands confined to narrow shoreface sediments. However, the preservation of ebb-tidal channels. Workers studying Holocene and modern bayhead VARIABILITY IN WAVE-DOMINATED ESTUARY RESERVOIRS 133

Fig. 13. A) Summary of reservoir properties of the various estuarine sandstones in the Bluesky Formation (Note: 1 Section = 1.6 km by 1.6 km). A consistent 80% bitumen saturation was utilized for all BIP calculations. Characteristics related to resource quality (porosity and shaliness) are compared in (B) while characteristics associated with resource size (area and thickness) are compared in (C).

delta deposits have recognized the localized nature in associated TIDAL-CHANNEL AND TIDAL-FLAT RESERVOIRS upper estuarine sediments (Nichol et al., 1997; Fig. 12D). The potential size of bayhead delta deposits (1.5 billion Although they locally exhibit excellent reservoir quality, barrels in the Bluesky Formation; Fig. 13A) and their high tidal-channel accumulations are characterized by high facies preservation potential, however, imply that this is an excep- variability. Locally, they are dominated by inclined heterolithic tionally important unit for prospective development. In fact, stratification and low vertical permeability relative to horizontal bayhead delta deposits have proven to be economical at many permeability (Strobl et al., 1997; Peijs-van Hilten et al., 1998). localities, such as in the Bluesky Formation of central Alberta Furthermore, they are generally thin and difficult to map. This is (Terzuoli and Walker, 1997), and in the development of the well illustrated in the McMurray Formation of northern Alberta Glauconitic Sandstone in southern Alberta (Broger et al., where reservoir rocks are almost exclusively composed of chan- 1997; Peijs-van Hilten et al., 1998). nel sands (Mossop and Flach, 1983; Wightman and Pemberton, 134 S.M. HUBBARD, M.K.. GINGRAS, S.G. PEMBERTON, AND M.B. THOMAS

1997; Ranger and Pemberton, 1997). In the McMurray intermediate-quality resources are present in strata associated Formation, channel trends cannot be projected in the subsurface, with flood- and ebb-tidal deltas and the bayhead delta. Tidal- despite exceptionally close well spacing (100 m). Even in out- channel and sandflat deposits represent the lowest quality crop, tidal-channel complexes can seldom be mapped. Channel resource. Despite the obvious limitations of this study, it sand reservoirs offer excellent reservoir quality, but are generally demonstrates the overall usefulness of accurately delineating present over a small area (Dekker et al., 1987). depositionally distinct sandstones in an oil or gas field. Sediments deposited in tidal-flat environments are considered to have the least resource potential because they are thin, often muddy, heterogeneous and have a complex areal distribution ACKNOWLEDGMENTS (Weimer et al., 1982; Gingras et al., 1999). In general, these are Funding for the subsurface component of this research was poor resource targets. provided by Shell Canada Limited. The analysis of modern deposits at Willapa Bay was supported by Exxon Production LIMITATIONS Research, Union Pacific Resources and Texaco Inc. Additional The application of this study has some obvious limitations, an understanding of which can allow the reservoir geologist to Table 5. Areal extent of modern estuary mouth sand bodies (compos- ite of tidal-inlet, tidal-delta and barrier sands) from various, modern apply the most useful aspects to any given estuarine reservoir. wave-dominated estuaries as compared with sandstones of the Bluesky Formation at Peace River. The length of sand bodies along 1) Dalrymple et al. (1992) defined wave-dominated and depositional dip is measured from the seaward end of the ebb-tidal tide-dominated estuaries as the estuarine facies model delta to the up-estuary edge of the flood tidal delta. end-members. The databases utilized in this study con- sist of wave-dominated (ancient) to mixed wave- and tide-influenced (modern) estuarine deposits. Where tidal energy is the predominant control on estuarine sediment distribution and sand body geometry, tidal channels, sandy tidal flats, and elongate sand bars comprise the most prospective reservoir units (Dalrymple and Zaitlin, 1989; Dalrymple et al., 1990). As presented in this paper, where wave energy is dominant, tidal-inlet, bar- rier-bar, tidal-delta, and bayhead delta sandstones typi- cally have the best reservoir potential. 2) There is no definitive, or diagnostic size of an estuary, and therefore the size of estuarine reservoir sand bodies is highly variable. Table 5 demonstrates the variability in areal extent of composite estuary mouth sand bodies (tidal inlet/tidal delta/barrier) from various modern estu- arine systems. Similarly, the dimensions of estuarine reservoirs from the subsurface of western Canada are also characterized by significant variability (Table 6). Controls on overall estuary size are numerous, including fluvial input, tidal range, depositional gradient, and tec- tonic setting (Zaitlin et al., 1994; 1995). The relative sizes of individual sandstone deposits from the various sub-environments will, in general, be proportional to one another regardless of the overall size of the estuary.

CONCLUSIONS The data presented herein stress the importance of identify- ing and mapping facies in hydrocarbon reservoirs located in estuarine deposits. The geological model provides the informa- tion that is necessary to 1) systematically and intelligently develop a reservoir; and 2) generate accurate reserve, resource, and deliverability assessments. Our case studies show that inlet, then barrier-bar deposits are the best resource, while VARIABILITY IN WAVE-DOMINATED ESTUARY RESERVOIRS 135

Table 6. Dimensions of various estuarine reservoirs from the subsurface of western Canada compared with dimensions of reservoir sandstones in the Bluesky Formation at Peace River.

funding was provided by Natural Sciences and Engineering ______and Posamentier, H.W. 1994. Transgressive facies and sequence archi- Research Council (NSERC) research grants to S.G.P. and tecture in mixed tide- and wave-dominated incised valleys: example from M.K.G. Ian Armitage, Bo Henk and Errin Kimball assisted in the Gironde Estuary, France. In: Incised-Valley Systems: Origin and Sedimentary Sequences. R.W. Dalrymple, R. Boyd and B.A. Zaitlin gathering field data at Willapa Bay. Critical reviews by Drs. (eds.). SEPM (Society for Experimental Geology), Special Publication Ed Clifton and Brian Zaitlin, as well as suggestions from 51, p. 225-240. Bulletin editor Lisa Griffith, significantly improved the Barwis, J.H. 1990. Flood-tidal delta reservoirs, Medora-Dickinson Trend, quality of the manuscript. North Dakota. In: Sandstone Petroleum Reservoirs. J.H. Barwis, J.G. McPherson and J.R.J. Studlick (eds.). Springer-Verlag, p. 389-412. Boyd, R., Dalrymple, R. and Zaitlin, B.A. 1992. Classification of clastic coastal depositional environments. Sedimentary Geology, v. 80, p. 139-150. REFERENCES ______and Honig, C. 1992. Estuarine sedimentation on the eastern shore of Nova Scotia. Journal of Sedimentary Petrology, v. 62, p. 569-583. Allen, G.P. 1991. Sedimentary processes and facies in the Gironde estuary: a ______and Penland, S. 1984. Shoreface translation and the Holocene strati- recent model for macrotidal estuarine systems. In: Clastic Tidal graphic record: examples from Nova Scotia, the Mississippi Delta and east- Sedimentology. D.G. Smith, G.E. Reinson, B.A. Zaitlin and R.A. ern Australia. Marine Geology, v. 60, p. 391-412. Rahmani (eds.). Canadian Society of Petroleum Geologists, Memoir 16, Broger, E.J.K., Syhlonyk, G.E. and Zaitlin, B.A. 1997. Glauconite sandstone p. 29-40. exploration: a case study from the Lake Newell Project, southern Alberta. 136 S.M. HUBBARD, M.K.. GINGRAS, S.G. PEMBERTON, AND M.B. THOMAS

In: Petroleum Geology of the Lower Cretaceous Mannville Group, Western Alberta. Unpublished M.Sc. thesis, University of Alberta, Edmonton, Canada. S.G. Pemberton and D.P. James (eds.). Canadian Society of Alberta, 124 p. Petroleum Geologists, Memoir 18, p. 140-168. ______, Gingras, M.K. and Pemberton, S.G. 2000. A sedimentological com- Cheel, R.J. and Leckie, D.A. 1990. A tidal-inlet complex in the Cretaceous parison of a Lower Cretaceous (Bluesky Formation) estuarine deposit from epeiric sea of North America: Virgelle Member, Milk River Formation, Alberta with modern and Pleistocene analogs at Willapa Bay, Washington. southern Alberta, Canada. Sedimentology, v. 37, p. 67-81. In: GeoCanada 2000: the Millennium Geoscience Summit, Joint Meeting Chiang, K.K. 1984. The giant Hoadley Gas Field, south-central Alberta. In: of the Canadian Geophysical Union, Canadian Society of Exploration Elmworth – Case Study of a Deep Basin Gas Field. J.A. Masters (ed.). Geophysicists, Canadian Society of Petroleum Geologists, Canadian Well American Association of Petroleum Geologists, Memoir 38, p. 297-313. Logging Society, Geological Association of Canada, and the Mineralogical Clark, J.E. and Reinson, G.E. 1990. Continuity and performance of an estuar- Association of Canada, May 29–June 2, 2000, Calgary, Alberta, ine reservoir, Crystal Field, Alberta, Canada. In: Sandstone Petroleum Conference CD, Abstract 136, 4 p. Reservoirs. J.H. Barwis, J.G. McPherson and J.R.J. Studlick (eds.). ______, Pemberton, S.G. and Howard, E.A. 1999. Regional geology and sedi- Springer-Verlag, p. 343-361. mentology of the basal Cretaceous Peace River Oil Sands deposit, north- Clifton, H.E. 1982. Estuarine Deposits. In: Sandstone Depositional central Alberta. Bulletin of Canadian Petroleum Geology, v. 47, p. 270-297. Environments. P.A. Scholle and D.S. Spearing (eds.). American ______, Thomas, M. and Zonneveld, J.P. 2001. The geometry and stacking Association of Petroleum Geologists, Memoir 31, p. 179-189. pattern of fan delta sand bodies in the Ostracode Zone, Alberta: improved ______1983. Discrimination between subtidal and intertidal facies in subsurface predictability through detailed stratigraphic analysis. In: 2001 Pleistocene deposits, Willapa Bay, Washington. Journal of Sedimentary American Association of Petroleum Geologists Annual Convention, Petrology, v. 53, p. 353-369. Official Program with Abstracts, v. 10, p. A94. ______and Phillips, R.L. 1980. Lateral trends and vertical sequences in estu- Luepke, G. and Clifton, H.E. 1983. Heavy-mineral distribution in modern and arine sediments, Willapa Bay, Washington. In: Quaternary Depositional ancient bay deposits, Willapa Bay, Washington, U.S.A. Sedimentary Environments of the Pacific Coast. M.E. Field, A.H. Bouma, I.P. Colburn, Geology, v. 35, p. 233-247. R.G. Douglas and J.C. Ingle (eds.). Pacific Section, Society of Economic Moslow, T.F. and Tye, R.S. 1985. Recognition and characterization of Paleontologists and Mineralogists, Pacific Coast Paleogeography Holocene tidal inlet sequences. Marine Geology, v. 63, p. 129-151. Symposium, no. 4, p. 55-71. Mossop, G.D. and Flach, P.D. 1983. Deep channel sedimentation in the Lower ______, ______and Anima, R.J. 1989. Sedimentary facies of Willapa Bay, Cretaceous McMurray Formation, Athabasca Oil Sands, Alberta. Washington. Second International Symposium on Clastic Tidal Deposits, Sedimentology, v. 30, p. 493-509. Canadian Society of Petroleum Geologists, Field Guide, 69 p. Nichol, S.L. 1991. Zonation and sedimentology of estuarine facies in an incised Dalrymple, R.W., Knight, R.J., Zaitlin, B.A. and Middleton, G.V. 1990. valley, wave-dominated, microtidal setting, New South Wales, Australia. Dynamics and facies model of a macrotidal sand-bar complex, Cobequid In: Clastic Tidal Sedimentology. D.G. Smith, G.E. Reinson, B.A. Zaitlin Bay-Salmon River estuary (Bay of Fundy). Sedimentology, v. 37, and R.A. Rahmani (eds.). Canadian Society of Petroleum Geologists, p. 577-612. Memoir 16, p. 41-58. ______and Zaitlin, B.A. 1989. Tidal sedimentation in the macrotidal Cobequid ______, Boyd, R. and Penland, S. 1994. Stratigraphic response of wave-domi- Bay-Salmon River estuary, Bay of Fundy. Second International nated estuaries to different relative sea-level and sediment supply histories: Symposium on Clastic Tidal Deposits, Canadian Society of Petroleum Quaternary case studies from Nova Scotia, Louisiana and eastern Australia. Geologists, Field Guide, 84 p. In: Incised-Valley Systems: Origin and Sedimentary Sequences. R.W. ______, ______and Boyd, R. 1992. Estuarine facies models: conceptual basis Dalrymple, R. Boyd and B.A. Zaitlin (eds.). SEPM (Society for and stratigraphic implications. Journal of Sedimentary Petrology, v. 62, Experimental Geology), Special Publication 51, p. 265-283. p. 1130-1146. ______, Zaitlin, B.A. and Thom, B.G. 1997. The Upper Hawkesbury River, Dekker, F. Visser, C. and Dankers, P. 1987. The Primrose-Kirby area in the New South Wales, Australia: a Holocene example of an estuarine bayhead southern Athabasca, Alberta, Canada; a detailed geological investigation. delta. Sedimentology, v. 44, p. 263-286. In: Exploration for heavy crude oil and natural bitumen. R.F. Meyer (ed.). Peijs-van Hilten, M., Good, T.R. and Zaitlin, B.A. 1998. Heterogeneity model- American Association of Petroleum Geologists, Studies in Geology 25, ing and geopseudo upscaling applied to waterflood performance prediction p. 507-520. of an incised valley reservoir: Countess YY Pool, southern Alberta, Dyson, I.A. 1998. Greensand reservoirs in siliciclastic shoreline systems: Canada. American Association of Petroleum Geologists Bulletin, v. 82, facies models for hydrocarbon exploration. The APEA Journal, Part 2, p. 2220-2245. p. 132-144. Phipps, J.B., Gage, B. and Caryl, J. 1976. Grain-size analyses of some Greys Frey, R.W. and Howard, J.D. 1986. Mesotidal estuarine sequences: a perspec- Harbor estuary sediment samples. In: Maintenance Dredging and the tive from the Georgia Bight. Journal of Sedimentary Petrology, v. 56, Environment of Greys Harbor, Washington. Appendix C, U.S. Army Corps p. 911-924. of Engineers, Seattle. Gingras, M.K. 1999. Applications in ichnology, neoichnology, and sedimentol- Ranger, M.J. and Gingras, M.K. 2001. Geology of the Athabasca Oil Sands. ogy. Unpublished Ph.D. thesis, University of Alberta, Edmonton, Alberta, Rock the Foundation Convention, June 18–22, 2001, Canadian Society of 592 p. Petroleum Geologists, Field Guide. ______, Pemberton, S.G., Saunders, T. and Clifton, H.E. 1999. The ichnology ______and Pemberton, S.G. 1997. Elements of a stratigraphic framework for of modern and Pleistocene brackish-water deposits at Willapa Bay, the McMurray Formation in the south Athabasca area, Alberta. In: Washington: variability in estuarine settings. Palaios, v. 14, p. 352-374. Petroleum Geology of the Lower Cretaceous Mannville Group, Western Howard, J.D. and Frey, R.W. 1973. Characteristic physical and biogenic sedi- Canada. S.G. Pemberton and D.P. James (eds.). Canadian Society of mentary structures in Georgia estuaries. American Association of Petroleum Geologists, Memoir 18, p. 263-291. Petroleum Geologists Bulletin, v. 57, p. 1169-1184. Reinson, G.E. 1992. Transgressive barrier island and estuarine systems. In: Howard, R.H. and Whitaker, S.T. 1990. Fluvial-estuarine valley fill at the Facies Models: Response to Sea Level Change. R.G. Walker and N.P. James Mississippian-Pennsylvanian unconformity, Main Consolidated Field, (eds.). Geological Association of Canada, p. 179-194. Illinois. In: Sandstone Petroleum Reservoirs. J.H. Barwis, J.G. McPherson ______, Clark, J.E. and Foscolos, A.E. 1988. Reservoir geology of Crystal and J.R.J. Studlick (eds.). Springer-Verlag, p. 319-341. Viking Field, Lower Cretaceous estuarine tidal channel-bay complex, Hoyt, J.H. and Henry, V.J. 1967. Influence of island migration on barrier island south-central Alberta. American Association of Petroleum Geologists sedimentation. Geological Society of America Bulletin, v. 78, p. 77-86. Bulletin, v. 72, p. 1270-1294. Hubbard, S.M. 1999. Sedimentology and ichnology of brackish water deposits Reynauld, J.Y., Tessier, B., Proust, J.N., Dalrymple, R., Bourillet, J.F., DeBatist, in the Bluesky Formation and Ostracode Zone, Peace River Oil Sands, M., Lericolais, G., Berne, S. and Marsset, T. 1999. Architecture and VARIABILITY IN WAVE-DOMINATED ESTUARY RESERVOIRS 137

sequence stratigraphy of a late Neogene incised valley at the shelf margin, Tye, R.S. and Moslow, T.F. 1992. Tidal inlet reservoirs: insights from modern southern Celtic Sea. Journal of Sedimentary Research, v. 69, p. 351-364. examples. In: Marine Clastic Reservoirs. E.G. Rhodes and T.F. Moslow Roy, P.S. 1984. New South Wales estuaries: their origin and evolution. In: (eds.). Springer-Verlag, p. 77-99. Coastal Geomorphology in Australia. B.G. Thom (ed.). Academic Press Weimer, R.J., Howard, J.D. and Lindsay, D.R. 1982. Tidal flats and associated Australia, p. 99-121. tidal channels. In: Sandstone Depositional Environments. P.A. Scholle and ______1994. Holocene estuary evolution – stratigraphic studies from south- D. Spearing (eds.). American Association of Petroleum Geologists, Memoir eastern Australia. In: Incised-Valley Systems: Origin and Sedimentary 31, p. 191-245. Sequences. R.W. Dalrymple, R. Boyd and B.A. Zaitlin (eds.). SEPM Wightman, D.M. and Pemberton, S.G. 1997. The Lower Cretaceous (Aptian) (Society for Experimental Geology), Special Publication 51, p. 242-263. McMurray Formation: an overview of the Fort McMurray area, northeast- ______, Cowell, P.J., Ferland, M.A. and Thom, B.G. 1994. Wave-dominated ern Alberta. In: Petroleum Geology of the Lower Cretaceous Mannville coasts. In: Coastal Evolution. R.W.G. Carter and C.D. Woodroffe (eds.). Group, Western Canada. S.G. Pemberton and D.P. James (eds.). Canadian Cambridge University Press, p. 121-186. Society of Petroleum Geologists, Memoir 18, p. 312-344. ______, Thom, B.G. and Wright, L.D. 1980. Holocene sequences on an Willis, A.J. and Moslow, T.F. 1994a. Sedimentology and stratigraphy of tidal embayed high-energy coast: an evolutionary model. Sedimentary inlet reservoirs in the Triassic Halfway Formation, Wembley Field, Alberta. Geology, v. 26, p. 1-19. Bulletin of Canadian Petroleum Geology, v. 42, p. 245-262. Saunders, T.D.A. 1989. Trace fossils and sedimentology of a Late Cretaceous ______and ______1994b. Stratigraphic setting of transgressive barrier-island progradational barrier island sequence: Bearpaw-Horseshoe Canyon reservoirs with an example from the Triassic Halfway Formation, Wembley Formation transition, Dorothy, Alberta. Unpublished M.Sc. thesis, Field, Alberta, Canada. American Association of Petroleum Geologists University of Alberta, Edmonton, Alberta, 187 p. Bulletin, v. 78, p. 775-791. Sexton, W.J. and Hayes, M.O. 1996. Holocene deposits of reservoir-quality Yang, C.S. and Nio, S.D. 1989. An ebb-tide delta depositional model – a com- sand along the central South Carolina coastline. American Association of parison between the modern eastern Scheldt tidal basin (southwest Petroleum Geologists Bulletin, v. 80, p. 831-855. Netherlands) and the Lower Eocene Roda Sandstone in the southern Smith, D.G. 1989. Comparative sedimentology of mesotidal (2 to 4 m) estuar- Pyrenees (Spain). Sedimentary Geology, v. 64, p. 175-196. ine channel point bar deposits from modern examples and ancient Zaitlin, B.A., Dalrymple, R.W. and Boyd, R.A. 1994. The stratigraphic organ- Athabasca Oil Sands (Lower Cretaceous), McMurray Formation. In: ization of incised-valley systems associated with relative sea-level change. Modern and ancient examples of clastic tidal deposits – a core and peel In: Incised-Valley Systems: Origin and Sedimentary Sequences. workshop. G.E. Reinson (ed.). Canadian Society of Petroleum Geologists, R.W. Dalrymple, R. Boyd and B.A. Zaitlin (eds.). SEPM (Society for p. 60-65. Experimental Geology), Special Publication 51, p. 45-60. ______, Meyers, R.A. and Jol, H.M. 1999. Sedimentology of an upper-mesoti- ______, ______, ______, Leckie, D. and MacEachern, J. 1995. The strati- dal (3.7 m) Holocene barrier, Willapa Bay, SW Washington, U.S.A. Journal graphic organization of incised valley systems: implications to hydrocar- of Sedimentary Research, v. 69, p. 1290-1296. bon exploration and production. Canadian Society of Petroleum Strobl, R., Muwais, W.K., Wightman, D.M., Cotterill, D. and Yuan, L.P. 1997. Geologists, Short Course, 189 p. Application of outcrop analogues and detailed reservoir characterization to ______and Shultz, B.C. 1990. Wave-influenced estuarine sand body, Senlac the AOSTRA Underground Test Facility, McMurray Formation, north east- heavy oil pool, Saskatchewan, Canada. In: Sandstone Petroleum ern Alberta. In: Petroleum Geology of the Lower Cretaceous Mannville Reservoirs. J.H. Barwis, J.G. McPherson and J.R.J. Studlick (eds.). Group, Western Canada. S.G. Pemberton and D.P. James (eds.). Canadian Springer-Verlag, p. 363-387. Society of Petroleum Geologists, Memoir 18, p. 375-391. Terzuoli, A. and Walker, R.G. 1997. Estuarine valley fills in the Lower Manuscript received: April 12, 2001 Cretaceous Bluesky Formation, Edson area, Alberta. Bulletin of Canadian Petroleum Geology, v. 45, p. 194-217. Revised manuscript accepted: August 28, 2001