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From Source to Trap: A Review of the Bakken Petroleum System, Upper Devonian­Mississippian, Southeastern Saskatchewan

Steve Halabura 1, Luis Buatois 2, Solange Angulo 2, and Lola Piché 1

Halabura, S., Buatois, L., Angulo, S., and Piché, L. (2007): From source to trap: a review of the Bakken petroleum system, Upper Devonian­Mississippian, southeastern Saskatchewan; in Summary of Investigations 2007, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2007-4.1, CD-ROM, Paper A-4, 8p.

Abstract

The Bakken Formation represents a petroleum system that can be tracked from source rock to trap within the same lithostratigraphic unit. This formation is present in the subsurface of the Williston Basin in North Dakota, Montana, Saskatchewan, and Manitoba and consists of three thin, but relatively uniform clastic units, from base to top: 1) a lower black shale, 2) a middle fine-grained calcareous or dolomitic siltstone and sandstone, and 3) an upper black shale. The black shales represent source rocks and most likely accumulated as suspension fallout on an anoxic shelf below storm wave base during basin-wide transgressions. The middle Bakken member presents the greatest reservoir potential and records both lithofacies variability and complex stratal architecture. Keywords: Bakken Formation, Late Devonian, Early Mississippian, Williston Basin, Western Canada Sedimentary Basin, sedimentology, sequence stratigraphy, ichnology, ichnofacies, petroleum systems, source rocks, Saskatchewan.

1. Introduction

The Bakken Formation represents a petroleum system that can be tracked from source rock to trap within the same formation. This formation is informally subdivided into three members (Figure 1). The lower and upper Bakken members consist of black shale that was most likely deposited in shelf environments under anoxic conditions (Smith and Bustin, 1996). The middle member comprises siltstone and sandstone with a minor portion of oolitic calcarenite and limestone (Christopher, 1961; Smith and Bustin, 1996), and records a wide variety of shallow- to marginalmarine depositional environments. The black shale members represent source rocks, whereas the middle member exhibits greater reservoir potential (Kreis et al., 2005, 2006). Fractures amplify low porosity and permeabilities in source rocks and provide an increase in accumulation space and an escape route for hydrocarbons in the tight shales. Where secondary fractures connect to regional faults or porous sands of the middle Bakken, migration over long distances can result. Structural activity contributes to fracturing in thermally mature areas, provides controls on migration pathways, and creates structural traps. Salt dissolution structures may create local stratigraphic traps within the Bakken middle member. A project recently started by the authors will include: 1) a detailed study of the sedimentology and ichnology of the Bakken Formation in cores, 2) correlation of cores and geophysical logs, 3) integration of all data to provide increased resolution of facies classification and to help interpret depositional environments in a sequence stratigraphic framework, and 4) application of the integrated analysis to reservoir characterization and petroleum exploration. While detailed facies analysis provides information to describe and interpret reservoir deposits, the evaluation of the associated biogenic structures helps in reservoir characterization in several ways, including delineation of key stratal surfaces, detection of subtle facies changes, and correlation of surfaces and stratal packages (e.g., Buatois et al., 2002). In this paper, we review previous work on the Bakken petroleum system and summarize some observations relevant to exploration for new hydrocarbon pools in the Bakken Formation of southeastern Saskatchewan.

2. Geological Framework and Stratigraphic Nomenclature

The Bakken Formation is distributed throughout the subsurface of the Williston Basin in North Dakota, Montana, Saskatchewan, and Manitoba (LeFever, 1991; Martiniuk, 1991; Christopher, 1961; Meissner, 1978; Smith and Bustin, 2000; Kreis and Costa, 2005; Kreis et al., 2005, 2006) (Figure 2) and consists of three thin, relatively

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North Rim Exploration Ltd., Suite 210, 3502 Taylor Street, Saskatoon, SK S7H 5H9; E-mail: [email protected] Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2; E-mail: [email protected]

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UNITS/SUB-UNITS COMPOSITE DESCRIPTION

LeFever, et al. (1991)

Thraster (1985) Christopher Smith and Karma and (1961) Bustin (1996) Parslow (1989)

Devonian

Middle Member

Bakken Formation

Mississippian

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LITHOFACIES

Smith and Bustin (1996)

Upper Member

SK MB 4 3 3 B4 B3 2 1 B1 1 A A 1 B1 A 2 SK, ND

SILTSTONE, massive, dense, mottled, dolomitic, argillaceous, grey green, fossiliferous, disseminated pyrite, rhythmites up to 15 cm thick in lower half of section (occasionally fossil-rich), slightly bioturbated, contact with upper member sharp.

ND SK 7 6 5 4 3 2

SK, ND C Mb SMm, SMh Sw, Sl

C B3

PARALLEL INTERBEDS OF DARK GREY SHALE AND BUFF SILTY SANDSTONE, moderately bioturbated, vertical burrows, calcareous, disseminated pyrite, overall coarsening-upward, flame and load structures at base of coarse laminae, rhythmites up to 10 cm thick, upper half may display trough cross-bedded sandstone beds, gradational lower contact with underlying unit.

2

SANDSTONE, tripartite division with upper and lower third wavy and flaser bedded silty sandstone gradational to and from the middle coarse-grained sandstone which may be massive and/or bedded (trough and tabular cross-bedding, inclined and horizontal laminae, and swash cross-stratification) with pebble and fossil-rich lags (shale clasts up to 4 cm diameter where B2 overlies the lower member, and feldspar clasts). Mainly quartzose with minor feldspar and heavy minerals, diastems, rhythmites, few brachiopods, disseminated pyrite, buff to green, calcareous, slight to no bioturbation.

B2 B1

B2

B

Sf, Sr, St, Lo Sw, Sl A SMm, SMh Mb

PARALLEL INTERBEDS OF DARK GREY SHALE AND BUFF SILTY SANDSTONE, moderate to very strong bioturbation disrupting laminae, dolomitic becoming calcareous with depth, disseminated pyrite, fossiliferous, lower contact gradational, upper contact gradational or erosive where channelling, grey green. SILTSTONE, massive, dense, mottled, bioturbated, very calcareous, argillaceous, grey green, highly fossiliferous, random orientation of fossils, disseminated pyrite, lower contact may be either gradational over several centimeters or erosive.

Lower Member

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Figure 1 - Informal stratigraphy of the Bakken Formation, including units and sub-units used by various authors. Also shown is a composite lithological description of the middle Bakken member compiled from published literature (modified from LeFever et al. (1991) and Smith and Bustin (1996)).

N

60

O

ALBERTA

Bakken and Exshaw Formations Western Interior of North America

SCALE

MILES KILOMETRES

uniform clastic members. The Bakken Formation was formally defined by Nordquist (1953) for the section between 9,615 and 9,720 ft (2031 to 2963 m) in the Amerada Petroleum Corporation H.O. Bakken No. 1 well, CSWNW Sec. 12, T157N, R95, Williams County, North Dakota. The Bakken has been mapped by correlating similar lithologies (the formation approach) or by using marker-defined facies that are assumed to be chronostratigraphic. Papers on the stratigraphy and petroleum potential of the Bakken Formation include those by Kents (1959), Christopher (1961), Thrasher (1985), Karma and Parslow (1989), LeFever et al. (1991), Smith and Bustin (1995, 1996, 2000), Smith et al. (1995), Kreis and Costa (2005) and Kreis et al. (2005, 2006).

0 0

40 64

60 128

S EX

The Bakken members exhibit an onlapping relationship to underlying strata, with each having a greater areal extent than its predecessor and all three thinning to zero toward the Figure 2 - Regional extent of Bakken/Exshaw Formation (based on Smith et al., eastern, southern, and northern 1995). margins of the Williston Basin (Smith and Bustin, 2000). Along the northern margins of the basin in central Saskatchewan, the Bakken Formation is truncated by the sub-Mesozoic unconformity. To the west, in Alberta and British Columbia, the lower and middle Bakken members correlate with the Exshaw Formation, and the upper Bakken with the basal black shale unit of the Banff Formation (Smith et al., 1995).

Late Devonian to Early Mississippian in age, as determined by conodont biostratigraphy, the formation overlies truncated and weathered Upper Devonian Big Valley and Torquay formations in Saskatchewan, the Lyleton Formation in Manitoba, and Three Forks Formation in North Dakota and Montana (Smith et al., 1995; Christopher, 1961), and is conformably overlain by the Lodgepole Formation (Lower Mississippian) in North Dakota and Manitoba and the Souris Valley Beds in Saskatchewan (LeFever et al., 1991).

3. Description of the Bakken Members

a) The Lower Member

The lower Bakken member is represented by lithofacies Mb of Smith and Bustin (1996) consisting of finely laminated, organic-rich black mudstone. In the deeper portions of the basin, it is considered to be a mature source rock with an average of 8% TOC (total organic carbon by weight) and a maximum 20% TOC (Smith and Bustin, 1995). The organic component is almost entirely marine algal (Bustin and Smith, 2000), and is distributed throughout the member in thin (<0.1 mm) discontinuous, amorphous, micro-laminae (Smith and Bustin, 1995). The shale averages 3 m in thickness over the Williston Basin, and has a maximum thickness of 20 m at the basin depocentre immediately east of the Nesson Anticline in North Dakota (LeFever et al., 1991; Smith and Bustin, 1998). The thickness in Saskatchewan ranges from 6 to 8 m, except for areas of local thickening such as SohioLeakville #1 (4-11-14-26W2M) where the lower member is 13 m in thickness (Christopher, 1961). In central and western Saskatchewan, the lower Bakken shale overlies the Big Valley Formation, but in eastern Saskatchewan overlaps the latter onto the Torquay Formation. It terminates under the middle member at an erosional edge in Range 31 west of the First Meridian (Christopher, 1961). Farther eastward, the lower Bakken shale is present as an

Saskatchewan Geological Survey

Ea rn ste

110

O

102

O

W HA ION AT RM FO

?

SASKATCHEWAN

MANITOBA

r efo fd it o lim

ti ma on

BAKKEN FORMATION 49

O

?

49

O

MONTANA

NORTH DAKOTA

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outlier in the Daly area of Manitoba (Martiniuk, 1991). Fossils include the conodonts Palmatolepis gracilis signoidalis, Palmatolepis rugosa rugosa, and Bispathodus jugous, of the late Famennian Lower-Middle expansa Zone (Karma, 1991), as well as brachiopod, gastropod, cephalopod, bivalve, ostracode, and arthropod remains and fish scales (Thrasher, 1985).

b) The Middle Member

The middle Bakken member displays a wide variety of lithofacies and has been informally subdivided into three units, A, B, and C (Christopher, 1961; LeFever et al., 1991; Smith and Bustin, 1995, 1996). Unit A consists of dark grey to greenish grey, intensely bioturbated, massive, calcareous, highly fossiliferous siltstone that is included in lithofacies SMm and SMh of Smith and Bustin (1996). Unit B comprises sub-units B1, B2, and B3 (LeFever et al., 1991). Sub-unit B1 is a dark grey, parallel-laminated, fossiliferous siltstone and grey-green, intensely bioturbated silty sandstone, which are equivalent to lithofacies Sw and Sl of Smith and Bustin (1996). Sub-unit B2 comprises: 1) greenish grey, massive, current rippled, cross-laminated or trough and planar cross-bedded, calcareous, coarse- to very fine-grained sandstone; 2) heterolithic sandstone-siltstone strata characterized by flaser bedding and mud drapes; and 3) locally developed, tight oolitic limestone. Bioturbation is distinctly less than in the underlying subunit; some beds are nonbioturbated. B2 is equivalent to lithofacies Sf, Sr, St, and Lo of Smith and Bustin (1996). Sub-unit B3 comprises dark grey, parallel-laminated siltstone and slightly bioturbated, calcareous, very fine-grained silty sandstone that are included in lithofacies Sl and Sw of Smith and Bustin (1996). Unit C is a grey and green, massive, dolomitic, argillaceous, slightly bioturbated, fossiliferous siltstone (lithofacies SMh and SMm of Smith and Bustin, 1996). Conodonts are extremely rare, although, in a summary table provided by Smith and Bustin (1996), the praesulcata, sulcata, duplicata, and sandbergi zones (from base to top) are noted as occurring in the middle member. These authors placed the Devonian-Mississippian boundary at the contact between units A and B. Brachiopods have been found (Rhipidomella missouriensis being the most common), as well as rare syringoporid corals, bivalves, crinoids, and trilobites (Thrasher, 1985). The middle member contains on average less than 1% TOC with rare concentrations of up to 7% TOC in mudstone layers (Smith and Bustin, 1998). For this reason, the middle Bakken is not considered to be a source rock, but rather the unit in which hydrocarbons have migrated and have been trapped under suitable conditions. The middle Bakken member overlaps the depositional and/or erosional edge of the lower member (Christopher, 1961; LeFever et al., 1991; Martiniuk, 1991; Smith and Bustin, 2000). All the units are at maximum thickness near the centre of the Williston Basin in North Dakota and thin to zero toward its northern, southern, and eastern margins. West of Saskatchewan, all three sub-units continue into the Exshaw Formation (Smith and Bustin, 2000). The total thickness of the middle Bakken member averages 13 m in the Williston Basin with a maximum of 30 m (Smith and Bustin, 2000). Regions of significant thickness are observed: near the depocentre just east of the Nesson Anticline in North Dakota; in the Waskada area of Manitoba; and in the "Elbow Sub-basin", the "Herald Embayment", and the "Torquay Embayment" in southern Saskatchewan (Christopher, 1961; LeFever et al., 1991; Smith and Bustin, 1998). Areas of significant thinning include the basin margins, and the broad Regina-Melville platform of east-central Saskatchewan (Christopher, 1961).

c) The Upper Member

The upper member corresponds to lithofacies Mb of Smith and Bustin (1996) and consists of a dark grey to brownish-black to black fissile, noncalcareous, carbonaceous and bituminous shale (Christopher, 1961) composed of illite and minor quartz, orthoclase feldspar, dolomite, and pyrite (Smith and Bustin, 1995). It has a higher content of conodonts and brachiopod shells than the lower member (Christopher, 1961), and an average TOC content of 10% with a maximum of 35% on the Regina-Melville platform in Saskatchewan (Smith and Bustin, 2000). Karma (1991) noted that the conodont information from this member is not precise because the available specimens of Siphonodella , the most diagnostic genus, are fragmented. However, Bispathodus aculeatus aculeatus are present which date the unit as not younger than the Lower Siphonodella crenulata Zone (Middle Kinderhookian); the presence of "Spathognathodus" macer indicate that this unit may be confined to the Lower crenulata Zone (Karma, 1991). With the exception of a few planktonic forms, megafossils are scarce (Thrasher, 1987). The upper member has an average basin-wide thickness of 2 m (Smith and Bustin, 2000), but attains maxima of 9 m (28 ft) in North Dakota, 4 m (12 ft) in Saskatchewan, and 18 m (59 ft) in the Waskada area of Manitoba. The last of these is attributed to contemporaneous salt dissolution in underlying Devonian formations (Martiniuk, 1991). The depocentre of the upper member is, however, poorly defined. The upper Bakken member, by overlap of the middle Member, presents the largest surface area of the three Bakken members.

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4. Depositional Environments and Sequence Stratigraphy of the Bakken Members

No clear modern analogue for the conditions that led to the deposition of the organic-rich black shales has yet been identified, so interpretations of the depositional environment of the two black shales of the Bakken Formation vary greatly through the literature. Fuller (1956) and McCabe (1959) suggested deposition in vast swamps. Christopher (1961) interpreted a restriction of free-flow water in a shallow sea due to sags and swells. Lineback and Davidson (1982) and Webster (1982) attributed the deposition of the black shales to a stratified water column (LeFever et al., 1991). However, general agreement suggests that the depositional environment for both the lower and upper Bakken member shales was characterized by similar conditions of anoxia, with fallout of suspended sediments on an anoxic shelf during basin-wide transgression being the most likely scenario. The Palmatolepis-Polygnathus biofacies imply relatively deep water (Karma, 1991), and the absence of wave-generated structures suggests deposition below storm wave base. Preservation of thin laminations and dark colours, and absence of bioturbation indicate anoxia. The abundant fauna preserved in the lower shale reflects fully marine conditions as opposed to marginal-marine brackish-water settings (e.g., swamps). In addition, layers with in situ or locally reworked benthic forms (e.g., rhynchonellid brachiopods) indicate brief periods of increased oxygenation. In contrast, the scarcity of megafossils in the upper Bakken supports more prolonged anoxia (Thrasher, 1985). Marine, oxygenated environments, ranging from the offshore to the shoreface have been interpreted for the middle member (Smith and Bustin, 1995, 1996). This is particularly evident in unit A and sub-unit B1, which are characterized by intense bioturbation and a rich fossil content. Smith et al. (1995) presented a five-part model of the depositional history of the Bakken that accounts for each member and unit of the Bakken Formation and the Exshaw Formation of Alberta. The lower Bakken member was deposited during a relative sea-level rise, thus being a transgressive systems tract, whereas the middle Bakken units A and B were deposited during a drop in sea level, and thus part of a lowstand systems tract. The middle member unit C together with the upper Bakken member forms a second transgressive systems tract.

5. Oil Generation and Migration

The geophysical log signatures of lower and upper Bakken members are characterized by: anomalously high gamma-ray radioactivity; anomalously low, but highly variable sonic velocity (high transit time); and either very high or very low resistivity (Meissner, 1978; Kreis and Costa, 2005; Kreis et al., 2005, 2006). Low sonic velocity is attributed mostly to the presence of a large amount of low-velocity organic material (Meissner, 1978); however, variance in electrical resistivity is the most important indicator of source rock maturity. Changes from low and normal shale resistivity of 2 to 15 ohm-m to very high resistivity values in deeper portions of the basin are thought to be caused by the generation of hydrocarbons (Meissner, 1978; Schmoker and Hester, 1990). Resistivity values alone, if calibrated, can be used to map thermally mature and immature areas and identify regions of oil generation (Schmoker and Hester, 1990; Kreis and Costa, 2005; Kreis et al., 2005, 2006). Our examination of a limited number of cores indicates that oil staining is widespread within the sand units of the middle Bakken, especially within the coarse-grained sandstones of sub-unit B2. Oil staining was also observed in current-bedded sandstones of sub-unit B2. Because of the high API gravity of Bakken oil, the oil stain in core often appears only as a light brown, "dusty" discolouration and requires fluorescence under ultraviolet light to clearly confirm the presence of oil. Migration pathways of Bakken hydrocarbons apparently extend long distances (Hansen and Long, 1991; Osadetz et al., 1991). For instance, the Rocanville pool in southeastern Saskatchewan is located 200 km from its source region (Osadetz et al., 1991).

6. Bakken Oil Production

Oil production in North Dakota and Montana is almost always from fractured reservoirs in thermally mature, overpressurized areas (LeFever, 1991; LeFever et al., 1991; Kreis and Costa, 2005; Kreis et al., 2005, 2006). The reservoirs are located in the lower portion of the Lodgepole Formation, all members of the Bakken Formation, and the upper part of the Three Forks Formation (Hansen and Long, 1991). The recovery of oil from these reservoirs depends on transmissibility created by abundant interconnected fractures such as at the Antelope Field, where wells perforated in any unit of the Bakken or the "Sanish Sand" of the underlying Torquay Formation are equally good producers (LeFever, 1991). In Saskatchewan, Bakken oil production is from the middle member at the three major producing Hummingbird, Roncott, and Rocanville pools, with minor volumes from isolated wells along the "Torquay-Rocanville Trend" (Christopher, 1961).

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The middle Bakken is also productive in Manitoba at Daly, Kola, and Birdtail, where oil is trapped in coarsegrained sand bodies deposited in erosional lows on the Lyleton surface (Martiniuk, 1991).

7. Exploration Considerations

The following observations are relevant to exploration for new hydrocarbon pools in the Bakken Formation of southeastern Saskatchewan: 1) The formation represents a petroleum system that can be tracked from source to trap. 2) Bakken hydrocarbons migrate over long distances, resulting in excellent exploration potential along the migration pathways. 3) Assembling a sequence stratigraphic framework that includes not only the Bakken, but also the Big Valley, Torquay, and lowermost Lodgepole Formations will be helpful. 4) The unit with the greatest reservoir potential is the middle Bakken member, especially the prograding (?) shoreface sands of unit B. 5) In that resistivity values of 35 ohm-m in the North Dakota depocentre correspond to areas capable of hydrocarbon production, resistivity values are important when evaluating thermally mature areas. 6) Local thermal anomalies enhance exploration potential by extending areas of thermal maturity. 7) Basement-controlled structures and structural inversions related to differential salt dissolution and collapse of overlying strata contribute to fracturing and provide controls on migration pathways and structural traps. 8) Salt dissolution structures may create local stratigraphic traps within the middle Bakken member. 9) Reservoirs may be present above and below the Bakken, particularly in areas of intense fracturing, or where porous Lodgepole carbonates or permeable sandstones of the Torquay Formation are in contact. 10) Important reservoir settings include: a) updip stratigraphic plays in middle member sandstones; b) downdip over-pressured and fractured reservoirs; c) thick middle Bakken sandstones associated with salt collapse structures; and d) stratigraphic plays associated with systems tract architecture.

8. Acknowledgments

Financial support for this study has been provided by Saskatchewan Industry and Resources. We thank Kim Kreis and Dan Kohlruss for reviewing this paper and for their useful comments.

9. References

Buatois, L.A., Mángano, M.G., Alissa, A., and Carr, T.R. (2002): Sequence stratigraphic and sedimentologic significance of biogenic structures from a late Paleozoic reservoir, Morrow Sandstone, subsurface of southwest Kansas, USA; Sediment. Geol., v152, p99-132. Christopher, J.E. (1961): Transitional Devonian-Mississippian Formations of Southern Saskatchewan; Sask. Dep. Miner. Resour., Rep. 66, 103p. Fuller, J.G.C.M. (1956): Mississippian Rocks and Oilfields in Southeastern Saskatchewan; Sask. Dep. Miner. Resour., Rep. 19, 72p. Hansen, W.B. and Long, G.I.W. (1991): Bakken production and potential in the U.S. and Canada, can the fairway be defined?; in Hansen, W.B. (ed.), Geology and Horizontal Drilling of the Bakken Formation, Mont. Geol. Soc., 1991 Guidebook, p69-88. Karma, R. (1991): Conodonts of the Bakken Formation (Devonian-Mississippian) in Saskatchewan, northern Williston Basin; in Christopher, J.E. and Haidl, F. (eds.), Sixth International Williston Basin Symposium; Sask. Geol. Soc., Spec. Publ. No. 11, p70-73. Karma, R. and Parslow, G.R. (1989): Sedimentology and geochemistry of the Bakken Formation (DevonianMississippian) in southern Saskatchewan; in Summary of Investigations 1989, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 89-4, p141-147.

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Kents, P. (1959): Three Forks and Bakken Stratigraphy in West Central Saskatchewan; Sask. Dep. Miner. Resour., Rep., 39p. Kreis, L.K. and Costa, A. (2005): Hydrocarbon potential of the Bakken and Torquay formations, southeastern Saskatchewan; in Summary of Investigations 2005, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2005-4.1, CD-ROM, Paper A-10, 10p. Kreis, L.K., Costa, A., and Osadetz, K.G. (2005): New perspectives on the hydrocarbon potential of Bakken and Torquay formations, southeastern Saskatchewan; URL <http://www.cspg.org/conventions/abstracts/2005Core/ kreis_l_hydrocarbon_potential_bakken_torquay.pdf>, accessed 28 Jan 2007. __________ (2006): Hydrocarbon potential of Bakken and Torquay formations, southeastern Saskatchewan; in Gilboy, C.F. and Whittaker, S.G. (eds.), Saskatchewan and Northern Plains Oil & Gas Symposium 2006, Sask. Geol. Soc., Spec. Publ. No. 19, p118-137. LeFever, J.A. (1991): History of oil production from the Bakken Formation, North Dakota; in Hansen, W.B. (ed.), Geology and Horizontal Drilling of the Bakken Formation, Mont. Geol. Soc., 1991 Guidebook, p3-17. LeFever, J.A., Martiniuk, C.D., Dancsok, E.F.R., and Mahnic, P.A. (1991): Petroleum potential of the middle member, Bakken Formation, Williston Basin; in Christopher, J.E. and Haidl, F. (eds.), Sixth International Williston Basin Symposium, Sask. Geol. Soc., Spec. Publ. No. 11, p74-94. Lineback, J.A. and Davidson M.L. (1982): The Williston Basin ­ sediment starved during the Early Mississippian; in Christopher, J.E. and Kaldi, J. (eds.), 4th International Williston Basin Symposium, Sask. Geol. Soc., Spec. Publ. No. 6, p125-130. Martiniuk, C.D. (1991): Regional geology and petroleum potential of the Bakken Formation, southwestern Manitoba; in Hansen, W.B. (ed.), Geology and Horizontal Drilling of the Bakken Formation, Mont. Geol. Soc., 1991 Guidebook, p43-68. McCabe, H.R. (1959): Mississippian Stratigraphy of Manitoba; Manit. Dep. Mines Nat. Resour., Mines Branch, Publ. 58-1, 99p. Meissner, F. (1978): Petroleum geology of the Bakken Formation, Williston Basin, North Dakota and Montana; in The Economic Geology of the Williston Basin: Montana, North Dakota, South Dakota, Saskatchewan, Manitoba, 1978 Williston Basin Symposium, Mont. Geol. Soc., Billings, p207-227. Nordquist, J.W. (1953): Mississippian stratigraphy of northern Montana; in Parker, J.M. (ed.), Little Rocky Mountains, Montana, Southwestern Saskatchewan, Billings Geol. Soc., 4th Annual Field Conference, September 10 to 12, Guidebook, p68-82. Osadetz, K.G., Snowdon, L.R., and Brooks, P.W. (1991): Relationships amongst oil quality, thermal maturity and post-accumulation alteration in Canadian Williston Basin (southeastern Saskatchewan and southwestern Manitoba); in Christopher, J.E. and Haidl, F. (eds.), Sixth International Williston Basin Symposium, Sask. Geol. Soc., Spec. Publ. No. 11, p293-311. Schmoker, J.W. and Hester, T.C. (1990): Formation resistivity as an indicator of oil generation ­ Bakken Formation of North Dakota and Woodford Shale of Oklahoma; The Log Analyst, January-February 1990, 9p. Smith, M.G. and Bustin, R.M. (1995): Sedimentology of the Late Devonian and Early Mississippian Bakken Formation, Williston Basin; in Hunter, L.D.V. and Schalla, R.A. (eds.), 7th International Williston Basin Symposium, Mont. Geol. Soc., Guidebook, p103-114. __________ (1996): Lithofacies and paleoenvironments of the Upper Devonian and Lower Mississippian Bakken Formation, Williston Basin; in Bull. Can. Petrol. Geol., v44, no3, p495-507. __________ (1998): Production and preservation of organic matter during deposition of the Bakken Formation (Late Devonian and Early Mississippian), Williston Basin; Palaeogeog. Palaeoclim. Palaeoecol., v142, p185200. __________ (2000): Late Devonian and Early Mississippian Bakken and Exshaw black shale source rocks, Western Canada Sedimentary Basin: a sequence stratigraphic interpretation; Amer. Assoc. Petrol. Geol. Bull., v84, p940-960.

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Smith, M.G., Bustin, R.M., and Caplan, M.L. (1995): Sequence stratigraphy of the Bakken and Exshaw formations: a continuum of black shale formations in the Western Canada Sedimentary Basin; in Hunter, L.D.V. and Schalla, R.A., (eds.), 7th International Williston Basin Symposium, Mont. Geol. Soc., Guidebook, p399409. Thrasher, L. (1985): Macrofossils and Biostratigraphy of the Bakken Formation (Devonian and Mississippian) in Western North Dakota; unpubl. M.Sc. thesis, Univ. North Dakota, Grand Forks, 292p. Webster, R.L. (1982): Analysis of Petroleum Source Rocks of the Bakken Formation (Devonian and Mississippian) in North Dakota; unpubl. M.Sc. thesis, Univ. North Dakota, Grand Forks, 150p.

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