Petroleum Potential of the Middle Member, Bakken Formation, Williston Basin

74 SIXTI-IINTERNATIONAL WILLISTON BASIN SYMPOSIUM

PETROLEUM POTENTIAL OF THE MIDDLE MEMBER, BAKKEN FORMATION, WILLISTON BASIN

JULIE A. LEFEVER Norlh Oakola Geological SlIITe), Grand Forks, Norlh OakOla, Uniled Slales 58202

CAROL D. MARTINIUK ManilOba Energy and Mines Winnipeg, ManilOba, Canada R3C 4E3

EDWARD F. R. DANCSOK AND PAUL A. MAHNIC Saskalchewan Energy and Mines Regina, Saskalchewan, Canada S4? 4V4

ABSTRACT The three members of the Bakken Formation exhibit an onlapping relationship, and converge and thin toward the margins The Bakken Formation is a widespread clastic unit between or marginal shelf areas of the Williston Basin. In Manitoba, the the Mississippian Madison Group and the Upper Devonian Big lower member is absent, except for Waskada field. Valley, Torquay, or Three Forks formations. The formation Several correlative lithofacies have been recognized in the typically consists of three members: a lower and upper organic­ middle member. The lowermost unit of the middle member is a rich shale and a middle calcareous sandstone and siltstone. regressive deposit. The upper portions of the middle member

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WYOMING

,-<-< SEDIMENTARY BASIN '00 o ENLARGED AREA

o,...... _!100 km r: 8A«EN OIL FIELDS 100m! D STUDY AREA

Figure 1: Index map showing. the location of th e stud y area within (h e Williston Basin . The apprO;(im:.lIe limit or the Bakk en. T orqu ay, and Oi~ Valley fomlalions is: ind i(,::Hed . Oil field s which are producing or h;lve produced rrolll lhe Bakken Forrn rlli on are al so shown. SIXTH INTERNA TI ONA L WILLISTON BA SIN SYMPOSIUM 75

SllO lV transgressive and regressive cycles, and intertidal deposit s major e rosional events are e videnced by strata from Cnmbrian to interfinger with their di stal equiva lents. Devonian time. The Devonian period marked a reori e nt ation of the seaway to the north as a result of activity along the Conventional Bakken production is restricted to areas where it Transcontinental arch. Devonian sediments show the repeated is a th ermally mature source rock. The greate r pari of Bakken transgressional-regressional cycles related to Elk Point basin product ion in recent years has been taken from the shale of the deposition. A re orientation of the seaways occurred again during upper and lower members, although there are outlying fields the Mississippian when the basin opened to the west through the which produce from a sandstone within the middle member. This central Montana trough . Terrestrial, marginal marine, and suggests that there has been a migration of Bakken oil from the evaporite sediments are represented by Pennsylvanian through central portion of the basin. The sandstone unit may provide a Triassic strata. The last sequence of marine strata was deposited conduit for migration. during the Jurassic and Cretaceous periods.

A major angular unconformity separates the Paleozoic from INTRODUCTION the Mesozoic strata and probably represents one or more periods The Bakken Formation has long been considered to be an of erosion that occurred from Late Mississippian to Early Jurassic impo rtant source rock for the oils of the Williston Basin. time. During this interval, Paleozoic strata in the northeastern part Numerous s tudies have examined the geochemistry and of the basin were uplifted and differentially eroded, while strata in hydrocarbon potential of the Bakken shales (Dow, 1974; the southern portion of the bas in were relatively unaffected Williams, 1974; Webster, 1982; 1984; Schmoker and Hester, (McCabe, 1959). Successively older Paleozoic s trata were 1983; Price e/ al., 1984). However, recent information indicates progressively truncated toward the basin margin. Deposition that a large amount of oil that has been produced and previously resumed during Mesozoic time, when a thick sequence of Jurassic thought to have been sourced by the Bakken Formation was, in and Cretaceous strata was deposited on the eroded Paleozoic fact, generated within the Lodgepole Formation (Osadetz and surface. Snowdon, in review; Osadetz e / al., in review). Within the Paleozoic i tsel f, an uncon form i ty sepa ra tes The hydrocarbon potential of the Bakken Formation has been Devonian and Mississippian strata and represents uplift and estimated to be at least 98 billion barrels (Webster, 1982; 1984). e rosion which occurred f ro m Late Devonian to Early Based on the recent findings of the Geological Survey of Canada, Mississippian time. During that interval, Devonian strata were a la rger amount of undiscovered Bakken oil exists somewhere uplifted and exposed along the basin margins, while deposition within the Williston Basin. Research indicates that this oil is continued in the deeper portions of the basin. MissiSSippian probably stratigraphically trapped within a narrow zone that sediments were later deposited on the eroded Devonian surface surrounds and includes the Bakken Formation. (Sandberg, 1964).

Conventional Bakken production in North Dakota is restricted In North Dakota, the Bakken Formation is a thin, clastic unit to areas whe re the Bakken is a thermally mature source rock. which straddles the Devonian-Mississippian boundary. It occurs However, well beyond there are fields in Saskatchewan and solely in the subsurface and consists of ihree informal units, Manitoba which produce from a sandstone within the middle referred to as the lower, middle, and upper members in this r~port. member of the Bakken. This suggests that there has been an The formation reaches a maximum thickness of 46 m (150 ft) in outward lateral migration of Bakken oil from the central portion the central portion of the basin (Fig. 2). of the Williston Basin. Recent focus on the Bakken Formation has The Bakken Formation subcrops in Manitoba along the been directed toward the development of and exploration for oil in northeastern portions of the study area, where it is unconformably the Bakken shales of North Dakota and Montana. This study will overlain by the "Red Beds" of the Amaranth Formation (Jurassic). examine the overall stratigraphy and petroleum potential of the Bakken Formation in North Dakota, Manitoba, and Saskatchewan Southeastern Saskatchewan is situated on the northern shelf (Fig. I). adjacent to the Williston Basin (Christopher, 1961 ). Sediments associated with the margin form a southerly-dipping wedge that thins towards the northern erosional edge. The strong southerly tilt GEOLOGICAL SETTING superimposed on these sediments occurred between Mississippian The Williston Basin is an intracratonic, structural, and and Jurassic time and is probably related to basin subsidence. sedimentary basin located at the western edge of the Canadian Shield. It occupies portions of North Dakota, South Dakota, Montana, Saskatchewan, and Manitoba (Fig. I). Gerhard e/ al. e 19 82) related the formation of the basin and other major structural features, includi ng the Nesson , Cedar Creek, a nd Bill ings anticlines, to a major directional change in th e structure of the Rocky Mountain belt.

Nea rl y continuous sedimentation has occurred in the North Dakota porti on of the Williston Basin. This is represented by over 4 ,878 m (16,000 ft) of sediments representing Cambrian through Tertiary time. Basin sedimentation is charac terized by cyclical transgressions and regressions with the repeated deposition of carbonates a nd clast ics. Pa leozoic s trata a re dominated by carbonates, whe reas Mesozoic and Cenozoic strata consist mainly of clastic rocks.

Figu re 2: tsopach map of (he B;\kken Fonnal ion for thl; ~(udy arc:.!. ConI om int ~r'\'J I Initial sedimentation occurred over an irregular Precambrian is 4 m ( 13 ft). Dashed line in northeastern Maniloba is the erosional limi t of Iht! surface. Repeated clast ic/carbonate sequences interrupted by Bak ken Formation. 76 SIXTH INTERNATION/IL WILLI TON BASIN SYMPOSIUM

GENERAL STRATIGRAPHY th e Upper Devonian T o rquay and Big Valley formations ill Saskatchewan. In tum, the formati on is overlain by Ihe Lodgepole A persistent sequence of black shales and grey siltstones was Formation (Lower Mississippian) throughout Nonh Dakota and recognized at the base of the Madison Group (Mississippian) Manitoba and by the Souris Valley Beds (Lower Mississippian) in limestones early in the exploration of the Williston Basin. These Saskatchewan. beds were referred to by a variety of names, including Kinderhook, Englewood, and Exshaw (Fuller, 1956). In an SW NW Sec. 12, T.157N ., R.9SW. AMERADA PETROLEUM CORP attempt to eliminate the confusion, a formal name, the Bakken, H.O. BAKKEN NO . I NORDOUIST. 1'353

CoR N(V was introduced into the literature in 1953 by the Williston Basin ~ w --' Nomenclature Committee of the Saskatchewan Society of l i..... IOf>t . --a'u"''''.. ,._P!\o''''. ~ ch,lr, . , U.I.~"l {lf1IJ'O 00_.. Petroleum Geologists and the Rocky Mountain Section of the g """'''''''''9'- 9 American Association of Petroleum Geologists. No formal definition for the formation was presented at that time. Sondl_, 1>QfI'.Q 9"o,-IHO)Wn, BAKKEN _, ';"'-9'O;l'

Nordquist (1953) formally defined and described the Bakken bf_ u,j1IOf.r"'alli",, I;~IO"" __ 60" Formation for strata occurring at depths from 2,931 to 2,963 m (9,615 to 9,720 ft) in the Amerada Petroleum Corporation - H.O. ""

Bakken # 1 deep test (Fig. 3). The well is located in CSWNW Sec. ()aIQ"'!o, ..

Kume (1963) modified Nordquist 's original description of the BAKKEN FORMATION Bakken type section. He re-evaluated the thicknesses of the members, modified the sample descriptions for the lower and Lower Member middle member, and designated a standard subsurface reference The lithology of the lower member of the Bakken Formation is section. The standard reference section is located over the interval uniform over the entire study area. It consists of a dark grey to from 3,059 to 3,078 m (10,035 to 10,095 ft)in the Socony brownish-black to black, non-calcareous, fissile, slightly to highly Vacuum Oil Company - C. Dvorak # 1 well (SENE Sec. 6, organic-rich shale. The colour of the shale varies depending on T.141 N., R.94.W, Dunn County, North Dakota). This well was the amount of silt versus clay versus carbon present in the rock. selected because it was continuously cored from the lower portion Lesser amounts of siltstone, limestone, and sandstone occur of the Madison Group (MiSSissippian) into the Birdbear within the lower member in North Dakota. The shale is finely Formation (Devonian). laminated to massive and can be hard or soft ("wax-like"). '

The Bakken Formation is formally recognized in southwestern In Saskatchewan, Fuller (1956) described a 2.5 cm (1 in) thick Manitoba, southern Saskatchewan, and eastern Alberta (Fuller, pebble bed at the base of the Bakken Formation. ConstilUents 1956; MacDonald, 1956; McCabe, 1959; Christopher, 1961; include dolostone fragments, occasional broken conodonts, and 1962; Carlson and LeFever, 1987). In southwestern Alberta, the chert in a grey siltstone matrix. Phosphatic fragments are also equivalent strata are divided into two formations: the basal black occasionally present. Fuller suggested that the pebble bed shale and middle siltstone member are included in the Exshaw represented the basal conglomerate of the Bakken Formation. Formation; and, the upper black shale is included with the basal Hayes (1984) described a thin, 2.5 cm (1 in), coarse, lag sandstone shales of the Banff Formation (MacDonald, 1956). Usage of bed at the base of the lower member in North Dakota. The Exshaw and Banff formations is carried into northern Alberta and sandstone bed contains fragments of conodonts, pyritized clasts, northern British Columbia. Correlations in northern Alberta and phosphatic particles, fish bones, subangular quartz sand and si lt, British Columbia become more difficult as the shale become chert, carbonate debris, and rounded pebbles all floating in a shale lithologically similar to the underlying and overlying beds matrix. (Macauley el al., 1961). Fossils identified by Hayes (1984) in the lower member in The Bakken Formation is an easily recognizable sequence on North Dakota include algal plant spores (Tasmaniles, sp.), wireline logs in the subsurface of the Williston Basin. As conodonts, inarticulate brachiopods (Lingula sp., Orbiculoidea previously stated, it comprises three mcmbers, a lower and an sp.), fish teeth, bones, and scales, conchostracans. rare ostracods, upper shale and a lithologically variable middle member. Readily woody plant fragments, and sponge spicules. Fossils identified in apparent on wireline logs. the sha les have abnormally high Saskatchewan include Lingula, conodonts, spores or spore-like gamma-ray readings (>200 API), low resistivity (ohm-m) readings remains including Tasmanilcs (Fuller, 1956; Christopher, 1961). in th e shal lower portion of the ba sin, high resistivity readings in the cle eper portion of the basin. and high transit times (80 to The lower shale is organic-ri ch in Ihe deeper portion of th e 120 microsec/ft) (Meissner, 1978; Webster, 1982; 1984). The basin and is considered to be a matut-e source rock. The organic middle member has nonnal wireline log characteristics for clastics materia l is distributed evenly throughout Ihe member. Pyrite is also abundant, and occurs in Ihin , wispy laminae. io lenses or and carbonates and becomes difficult to dis tinguish from the nodules, or disseminated throughollt th e interval. Fractures can underlying Three Forks Formatio n when the lower shale is absent. al so be present. can bc irregular and blocky or smooth and The three members of th e Bakke n Formation exhibit an conchoidal in the more siliceous sections. Occas ionally, the onlapping relationship; each successively higher member has a fractures are healed with calcite or pyrite. Resinous or vitreolls grc,llcr areal distribution. The formation overlies Ihe Three Forks pods of carbonaceous material ("dead oil") arc presenl along some l'ormation (Upper Devonian) in North DakOla and Manitoba. and of the fractures which occur parallel 0[' subp;[rallcl to bedding. SIXTH INTERNATIONAL WILLISTON BASIN SYMPOSIUM 77

The lowcr mcmber reaches a maximum thickness of 17 m The middle Illcmbel' attains a maximum thicKncss 01 27 nl (55 ft) in North Dakota with a well-defined depocenter (87 ft) in North Dakota, Its depocenter, like tile lower member, is immediately east of the Nesson anticline. Thicknesses in well developed and is located just to thc east of the Nesson Saskatchewan reported by Christopher (1961; 1962) for the lower anticline. In Manitoba, the Middle Member averages 4 m (13 ft) Bakken shale member generally range from 6 to 8 m (20 to 25 ft). in thickness and reaches a maximum thickness of 16 m (52 ft) in A local exception is the Sohio-Leakville #1 (4-11-14-26 W2M) the Waskada area. In the study area of Saskatchewan, the middlc where the lower Bakken shale member reaches a thickness of Bakken sandstone member reaches a maximum thickness of 18 m 13 m (43 ft). In Manitoba, the Lower Member is restricted to the (60 ft) in the Herald and Torquay embayments (Christopher. Waskada area (Townships I and 2; Ranges 25 and 26 WPM) and 1961). is a maximum 13 m (43 ft) thick (McCabe, 1959; Martinuik, 1988). Upper Member

Middle Member The upper member of the Bakken Formation is lithologically similar to the lower member and is also uniform throughout the The lithology of the middle member is highly variable in North study area (Fuller, 1956; McCabe, 1959; Christopher, 1961; 1962; Dakota. It consists of a light grey to medium dark grey Webster, 1982; Hayes, 1984; Martiniuk, 1988). It consists of dark interbedded sequence of siltstones and sandstones. Lesser grey to brownish-black to black, fissile, noncalcareous, amounts of shale, dolostones, and limestones rich in silt, sand, and carbonaceous and bituminous shale. It is more fossiliferous than oolites may also be present (Webster, 1982; Hayes, 1984; the lower shale. Christopher (1961; 1962) reported abundant Thrasher, 1985). The siltstones and sandstones are massive or conodonts and chonetid brachiopods. Hayes (1984) noted the coarsely bedded with an occasional trough or planar cross-bed set. presence of other fossils including fish teeth, bones, and scales. Much of the sequence is well sorted. Bioturbation commonly rare woody plant fragments, inarticulate brachiopods, and spores disturbs the bedding, especially in the more argillaceous portions. in addition to conodonts. He also noted that one well had a well Features indicative of soft sediment deformation, including developed layer of reworked, pyritized, articulate brachiopods. microfaults and flow structures, are also present. Cements include The upper member differs from the lower shale in North calcite, dolomite, silica, and pyrite. Insoluble residues comprise Dakota with the absence of crystalline limestones and greenish­ quartz silt and sand, feldspar, chert, glauconite, and silicified and grey shale beds and an increase in the organic content. Fractures pyritized fossils. are also present in the upper member. Thin, poorly defined Fossils within the middle member include articulate and less laminae of silt-sized quartz and carbonate grains occur common inarticulate brachiopods, pelmatozoan fragments, throughout. Small sandstone lag deposits were also described in gastropods, and various trace fossils. Conodonts, plant spores, and the upper member by Hayes (1984). These deposits are rich in ostracods were also observed but are considered to be rare (Hayes, conodonts, fish bones and teeth, and phosphatic particles and 1984). occur at several zones within the shale,

In Manitoba, the Middle Member consists primarily of a light The upper member reaches a maximum thickness of 9 m greenish-grey to reddish- and purplish-grey siltstone to very fine­ (28 ft) in North Dakota. The depocenter is poorly defined. In to medium-grained sandstone (Martiniuk, 1988). Much of the Saskatchewan, the shale is a maximum 4 m (12 ft) thick. sequence is dolomitic and argillaceous. Mineralogically, the averaging 1.2 m (4 ft). A uniform thickness of 2 m (7 ft) for sandstones consist predominantly of quartz with minor amounts of Manitoba is reported by Martiniuk (1988). In the Waskada area of feldspar. Coarser grain sizes are generally subrounded. The matrix Manitoba, the Upper Member attains a maximum thickness of is a dolomite or dolomitic shale, depending on the degree of 18 m (59 ft). sorting. Grain size increases in the northern and eastern portion of Depositional Environments the stud y area. A variety of environments have been suggested for the origin McCabe (1959) reported that often the Middle Member is of the two black shales of the Bakken Formation. Workers agree massive or finely laminated. Cross-bedding and contorted bedding that the environments of deposition were similar for the lower and were also noted. Several intraformational breccias and upper shales and that conditions were uniform over the area. conglomeratic zones observed near the base of the unit probably However, a wide range in ideas is possible when conditions represent diastemic and/or erosional breaks within the member. conducive for shale deposition vary from open marine to In Saskatchewan, Christopher (1961; 1962) divided the middle terrestrial swamp. sandstone member of the Bakken Formation into two units, A and Fuller (1956) suggested that the black shales were deposited in B. Unit A, the lowermost unit, consists of a massive, calcareous, a vast swamp resulting from the retreat of Devonian seas. Iron greenish-grey, pyritiferous, fossiliferous (primarily brachiopods), oxides and sulfides reworked from Qu' Appelle Group sediments very fine-grained to silty sandstone that is present in the north­ were reduced to form the iron sulfides of the Bakken muds, ,..I.. western, western and southern portion of Saskatchewan. Unit B transgression with the resulting incursion of seawater eroded the consists of an interfingering shale/sandstone sequence, designated stable margins and formed the arenaceous beds of the middle B I through B4. The shale units, B I and B3, occur west of the member. A final seaward retreat of waters was followed "ith the second meridian, East of the second meridian, the two sandstone return of conditions responsible for the formation of the black units, B2 and B4, come in contact to constitute the middle Bakken shales, sandstone member. The uppermost unit, B4, represents a massive, fossiliferous, silty sandstone or coarse siltstone. This unit, in turn, McCabe (1959) also suggested a marine swamp for the is underlain by B2. a fine- to medium-graincd, friable sandstone formation of the black shales, Restriction of cil'Clllation was due to which changes westward into a well cemented, calcareous, prolific organic development, During the deposition of the "Iiodle medium-graincd sandstone and oolitic calcarenite. Unit B2 Member, the swamp was drowned or flooded by an influ\ of exhibits well dcveloped cross-bedding, lipple marks, current scour shallow marine clastics derived from older Paleozoic or marks. and numerous diastems. Precambrian rocks, Stagnant. swamp conditions ,,'cre re- 78 SIXTH INTERNATIONAL WILLISTON BASIN SYMPOSIUM c';l;tb li "hed I'or Ihe dcposilion or Ihe Upper Member. McCabc was termina[ed by a major trans gression under which [h e SI;\Icd lilal Ih e underlying Three Forks, Ih e ovcrlying Lodgepole, <\['gi llaceous litllcstones of the Madison Group were deposited. and [he Middlc Member were de posited in shallow marine Webster (1982) and Lineback and Davidson (1982) suggested condilions; therefore the shales were also probably deposited in shallow marine to terrestrial environment. a stratified water column for the deposition of the black shales. Evidence presented by Webster in support of this idea includes Christopher (1961; 1962) attributed the environment of planar and thin laminations within the shale resulting from quiet deposition of the Bakken shales to a restriction of free flow water water deposition below wave base; presence of planktonic algal in a shallow sea due to sags and swells. Periodically fetid, the spores (Tasmallires sp.), fish remains, cephalopods. ostracods. study area covering Saskatchewan converted to tidal flats and conodonts. and inarticulate brachiopods; high amounts of organic b road swamps. Thick black muds accumulated locally in and pyritic material suggesting anaerobic conditions; uniformity sinkholes. Deposition of the middle Bakken sandstone member over a large area; and the predominance of amorphous-sapropelic occurred in response to the southwesterly tilt of the Saskatchewan organic matter over terrestrial material. A temperate climate could portion of the study area. Clastic sources of silt and clay were account for the lack of mixing between the bottom and surface introduced into the area from the northeast and east and filled in waters. The lithology and fossil content of the middle member basinal areas to the southeast, west, northwest and north. The suggests a return to aerobic marine conditions with moderate initial transgression of the middle Bakken seas resulted in the current activity. rapid deposition of clays and silts and the burial and preservation Age of abundant brachiopods. After the initi a l deposition of Christopher's "A" unit, the eastern area began to subside and the Early workers assigned a Mississippian age to the Bakken sea spread over the platform area of Saskatchewan to the flat shelf Formation based on litho logy and limited paleontological data area to the east and into Manitoba. This strandline and erosion of (Nordquist. 1953; Thomas. 1954; Fuller. 1956). McCabe (1959) the Devonian extended into Manitoba. The deposition of the "B" inc luded the Bakken as th e basal formation of the Mississippian unit followed with fine- to medium-grained sands intermittently system. This assignment was based on the absence of the Lower laid down on a broad shelf in shallow water of vuiable current Member of the Bakken over most of Manitoba and the evidence activity. Grey-black muds interfingered with the sands reflecting a of erosion at the top of the Three Forks Formation. both indicating "sea floor of flats, shoals, and broad hollows traversed by weak, a possible time break. Martiniuk (1988) also placed the Bakken in shifting currents" (Christopher, 1962, p. 76). Sedimentation Manitoba as the basal unit of the Mississippian sequence with the slowed and returned to swamp/ lagoonal conditions, under which systemic boundary inferred at the unconformity between the the upper Bakken shales were deposited. Bakken sedimentation Bakken and underlying Three Forks Formation.

Tabte 1: Composite lithofacie s descriptions and correlations for th e middle member of the Bakken Formation for the study area. Christopher ([ 961) divided the middle member into two units. A and B. Unit B was th en furth er subdivided into B I. B2. 83. and B4. Thrasher (1985) and Karma and Parslow (1989) used macrofossils and lithology to subdivide (he middle member imo three units. This study incorporales both divisions of Ihe middle member. LITHOFACIES

This Paper ------11 Thrasher, 19851 Christopher ,1961 Karma a Porslow ,1989

UPPER MEM8ER SK ND MB SK,ND SK

' ~ ....,:' SilTSTONE, massive, dense, mottled, dolomitic. argillaceous, g rey- green, fossiliferous, disseminated pyrite, rhythmites up to 4 15 em thick In lower hair of section (occasslonally fossil-rich), c 7 3 84 t1~ slightly bioturbated . contact with upper member sharp. 3

PARALLEL INTERBEDS OF DARK GREY SHALE AND BUFF SILTY SANDSTONE, moderately bioturbated, vertical burrows. calcareous. disseminated pyrite. overall coa rsening-upward. flame and load 6 structures at base of coarse laminae, rhythmites up to 10 em thick, B3 83 upper half may display trough cross-bedded sandstone beds, grada tional lower contact with underlying unit. 5

~ SANDSTONE, tripartite division with upper and lo wer third wavy .~ and rlaser bedded silty sandstone yradiltional 10 and from the middle coarse-grained sand s tone which may be ma s sive .and lor , bedded (trough and tabular cross-bedding. inclined .and horizontal 4 2 I laminae, and swash cross- stratification I with pebble and fossil - rich I lags (sh lomlt ic bf;'coming ca lCar" I;:Ou S with d e p th, dis s e minate d B I . PYrite , fO ~!l. ilif or ou s, lower ( o nta Cl gradational. u ppe r contact 81 ".: .. ' 9c.d. Uon,t oc " co >;vo whe," ch,nnct t;n9 . 9cey-gceen.

II~~ ~~~~I~~~O~;: ;~ :; f :. ~r'~ i:~~n~~9h7;{ ~~~~ili ~:;:usC,al~:~~:~ . .,, -; orientation of foss il s . d lueminateo pyrite . lower contact F-9t mily be e ither g nu1 1.1 tion,,1 oVl.."r s everal centimeters or A A erosive . rr cOliER MEMBER Slxtf-llNTERNATJONAL WILLISTON BASIN SYMPOSIUM 79

Cilr-istopiler ( 1961; 1962) placed tile sys temi c boundar-y at til e relations of the lithofacies identified, arc shown in Table t. The base of the middle Bakken sandstone me mbe r- in Saskatcilewan, re gional fe nce diagram (Fig. 4) s hows th e di stribution of the This decision was based on th e lack of Kinderhookian age fossil s various lithofacies over th e study ar-ea. in th e lower Bakken s hale member. Earlies t recognizable Kinderhookian age fossil s were desc ribed by Brindle ( 1960) in the NORTH DAKOTA middle sandstone member of the Bakken in Saskatchewan. Bakken Formation: Lower Member

Detailed paleontological studies have been conducted on the The lower member of the Bakken Formation overlies the Bakken Formation in North Dakota by Hayes (1984), Thrasher greenish-grey, argillaceous burrowed siltstone of the Three Forks (1985), and Holland el aI., (1987). These studies suggest that the Fonnation. The lowennost contact was observed only in one core Bakken Fonnation is Devonian and Mississippian in age. Using and was irreguiar and sharp. The contact was overlain by a bed conodont fauna from the shales, Hayes (1984) suggested that the containing small clasts of bitumen and fossil fragments. systemic boundary occurred at or near the contact between the middle and upper members. The uppe r membe r h as The lower member consists of a dark brown-black to black, characteristically lower Mississippian conodonts that are not the organic-rich shale. It can be massive and competent or fi ssile. earliest Kinderhookian . This s ugges ts that there is a hiatus Pyrite is generally disseminated throughout the shale; it also between the two that may coincide with a regionally extensive occurs in lenses, as nodules, or in laminations. In addition to unconfo rmity. Thrasher (1985) examined mac rofossi ls of the pyrite g rains, laminations fonned by the alignment of silt-sized middle member and concluded that the systemic boundary appears calcite grains are also present. Conodonts, ostracods, cephalopods, to be within the middle member. conchostracans, and brachiopods constitute the fossil assemblage of the shale. DETAILED STRATIGRAPHY A variety of fractures are associated with th e lower member. Thin, hair-like, vertical fractures occur in the more massive zones. The fo llowing is a detailed description of th e lithofac ies of the Conchoidal fractures are present when th e lithology show an Bakken Formation based on data derived from the examination of increase in s ilt content. Open bedding plane fractures w ith core in North Dakota, Saskatchewan, and Mani toba. Composite residual oil staining are also present. Closed vertical fra ctures are lithofacies descriptions of the middle member, showing the cor- generally cemented with calcite or pyrite or both. A well

:.- :.- '"~ :.- '" '" m'" '" '" "' ,..,'" ~ ,.., " ~ i': '01'0 o 0 m II SASKATCHEWAN MONTi\NA~~~~~

o I I I I I I t SCALE

EXPLA NATION Sltoli.-; rcpb'c Oolu m : Top of Middle Membet , z Lilh ofoc ie s Vni l!' '« 2 r- . '40 Me SK ... ° 7 l·. C ...z ...'" 5.6 8 3 r- <:> - z x j MIDDLE { 3 •• I, Z B2 0 1- ;:s MEMBER 2 B, "'n: ~ - z a,a , A °

LOWE R MeM BER: Shaded. wt'lerfJ pr esenl

Figure 4: Regioonl fence di agram showing the di slribulion of th e: 11Iho f:l ci .... s of the Illiddle member of the Bakke n Fo rm ~Hi o n . The lower member IS shaded wht: re pl ~'1 C: lI. Lithofaclc:; unit s w ilh their appropri ate numher or lellcr d(',ignati on Me shown so SIXTH INTERNATIONAL WILLISTON BASIN SYMPOSIUM

de ve loped brecc ia zO ll e with calc it e cement occ urs ill one well Litho fa c ies unit .1 is thc sandstone bed whi ch is prociucti ve ill (SWNE Sec. 2(), T.I S6N., R.91 W.). Limestone interbeds arc also Canada (Table I) . In I\orth Dakota , the bed is prominent both in prcse nt within thi s well. Many of the wells show small-scalc core and on wire line log,; (Fi g. 6) and easily mapped (Fig. 7) . It is det'o rmcd fractures , all o f which are cemented with calcite or a nledium grey, da rk gre y or greyish-tan, very fine- to fine ­ pyritc or both and are associated with laminations of silt-sized grained sandstone. Occasionally, th e grain si ze in creases into the pyrite and c alcite grains. Sizes range from 0.6 cm (.25 in ) to upper medium range. The sandstone is moderately we ll sorted to seve l·al centime tres. Christopher (1961) s uggested that these we ll sorted and can be poorly sorted locally. Grains are ge nerally "vertical fis sures" may have originated as mudcracks. well-rounded to rounded. Some of the finer gra ined material is subrounded to subangular. The sandstone consists predominantly The contact between the lower member and the middle of quartz with occas ional fe ldspar and heavy minerals. member is irregular and sharp or gradational. Beds containing Glauconite was observed in one well. Coarser grained material small clasts and fossil fragments commonly overlie the sharp, consists locally of rounded to subrounded ooid and crinoid irregular contacts. The gradational contacts show either a gradual fragments. In the wells where these sediments occur quartz is rare. decrease in argillaceous content to the siltstone/very fine- grained Pyrite grains or nodules are scattered throughOUt. The sandstone is sandstone lithology of the middle member or a sequence of cemented generally by calcite and occasionally by pyrite, alternating shale and siltstone/sandstone beds that decrease in argillaceous content vertically. The gradational contacts are Unit 3 consists commonly of an alternating sequence of restricted to the northernmost wells in North Dakota. massive, cross-bedded, and thinly laminated beds. The cross­ bedded and massive beds are generally coarser grained. The upper Bakken Formation: Middle Member portion may have multiple fining-upward sequences, whereas the Seven lithofacies were observed in the cores of the middle lower portion may display reverse grading. Other features member in northern North Dakota. These facies are correlative observed include load or channel forms grading upward into fine­ with those recognized in cores in Manitoba and Saskatchewan grained material, and calcite-filled fractures. Soft-sediment (Tabl e I and Fig. 4). Data are derived from Bakken core deformation was observed in the middle of the unit in a few cores. examined in 12 North Dakota we lls. The seven lithofac ies Unit 3 ranges in thickness from 0.2 to 4 .6 m (0.5 to 15 ft) , recogni zed in North Dakota, in ascending orde r, are as follows: averaging 2 m (8 ft) . The contac ts between Unit 3 and the Lithofacies Unit I consists of a light grey, greenish-grey, or overlying and underlying units are sharp. brownish-grey argillaceous siltstone. It is massive, cemented with Measured porosities range from 0.09 to 12.1 percent, and calcite, and has scattered pyrite nodules, and fossils. Fossils average 7 percent. Permeabilities range from 0.02 to 5.8 md, and generally include c rinoids and brachiopods. One well shows average 0.6 md. Oil staining appears to be restricted to the very abundant s mall brachiopods above the contact with the lower fin e-grained, thinly I.aminated quartz sandstone beds. shale. Burrowing is locally present. The lithofacies range in thickness from 0.5 to 1.8 m (1.5 to 6 ft). lntergranular porosity Lithofacies Unit 4 comprises interbedded light to medium and permeability for unit I in one well was determined to be 3.7 grey, argillaceous to sandy siltstones and brownish-grey, very percent and 0.01 md, respectively. fine-grained sandstones and local claystone. The sequence is commonly laminated. Laminations are generally irregular or wavy Lithofacies Unit 2 is greenish-grey to brownish-grey, bedded, or highly disturbed due to soft sediment deformation. argillaceous siltstone or sandy siltstone to a brownish-grey, very Cross-ripple laminations and reverse grading are also present. fine-grained sandstone. The unit ranges up to 10m (33 ft) in There are occasional lenses of coarser-grained material in which thi ckness. Small-scale clay drapes are present throughout, as well the intergranular pores are filled with pyrite. Some sections also as burrows filled with pyrite. In one well (NENW Sec. 35, show extensive pyrite-infilled burrowing. A 0 ,3 m (l ft) thick T . 156N., R.93W.), where the unit is 8 m (27 ft) thick, burrowing disturbed zone, due to soft-sediment deformation, is commonly is restricted to the upper 2 m (7 ft) and basal l.5 m (5 ft). present at the base of the unit. Scatte red fossils, crinoids and brachiopods, are present throughout. Identifiable brachiopods inc lude Chonetes ornatLis Unit 4 reaches a maximum of 2 m (6.5 ft) in thickness. The and Rhy/iophora areua/us. Fossils are generally partially or unit is generally not cemented. Cement, where present, consists of completely replaced with pyrite. dolomite.

Glauconite was noted in three wells over a restricted interval Measured pernleabiJities are low «0.0 I to 0.15 md). Overall ranging from 0.6 to l.2 m (2 to 4 ft). The glauconite is often porosities are higher than the lower lithofacies, and range from 3. 1 associated with burrows. Hematite staining was also noted in the to J 5.8 percent, averaging 8 percent. basal portion of one well. Cement, where present, consists of Lithofacies Unit 5 consists of an alte rnating sequence of calcite and appears where the interval is c oarser grained. medium grey, argillaceous siltstones, light 10 medium grey, very Porosities range from 1.2 to 8.4 percent, averaging 5.5 percent. fine- grained sandstones , and d a rk g rey shale . [t is thinly Permeabilities range from <0.0 I. to 0.41 md, averaging 0 .22 md. laminated. Laminations are either paralle l or slightly undulatory Unit 2 was oil productive in one well with treatment. and range in thi ckness from I to 5 mm (.04 to 0.2 in ), with grain One well, toward th e central portion o f th e basin (NENW Sec. size increasing slightly in th e thic ker lamin:l1 ions. The unit is 35 , T.I S6N., R.93W.), has an additional 5 III (1 6 ft) section locally cemented with dolomite. Several of the ,,·ell s e .\ hibit soft­ between units 2 and 3 which is not present in the othe r we ll. s (Fig. sedime nt deformati on as contorted bedding either at the top or 5). The basal bed consists of a laminated, slightly argi llaceous, oil bo tt o m of the interv a l o r a s sm a ll fold , a nd f,lults (po s t ­ sta ined, sandy s iltstone, which gradcs upward into a medium lithification) within. browni sh- grey, massive siltstone; an inte rbedded sequence of very Thicknesses of unit 5 ranges from 0.6 to I. l rn (2 to :U ft ). fi ne -gra i ned sandstone and c Ia ystone; and , a med i u m grey ish­ Pcrmeabilities range fro m <0.01 to 0. 56 mel . :I'·eraging 0. 2 Illd . brown. uni fo rmly laminated, oil-stained sequencc of s iltstone and Porosities range from 3.8 to 12 .4 percenl. and :I' ~ ra gc 7 perce n!. ve ry fin e -grained sandstone . Indi vidual sandstone bcel s are mode ­ rat c ly wcll sOI"t eel and some are lensoidal. Litho facies Unit 6 cOll si sts o f a n a lt c rnatin g sequence o f SIXTH INTERNATIONAL WILLISTON BASIN SYMPOSIUM 81

medium to light grey siltstone, dark grey claystone to brow n/b lac k sha lc; a nd , tan to li ght brownish-grey , very fin e-grai ned san ds ton e, siltstone, and sa ndstone beds that commonl y di splay planar or cross -ripple lam ina tions, The sequence occu rs as beds or len ses and is usu all y di srupted du e to burrow in g. The basal portion of th e unit (0.3 to 0.9 m; I to 3 ft) consists predominantly of a thinly lam in ated, very fine-grained sa ndstone and siltstone with abundant bu n ows. Argillaceous content varies locally and generally increases up ward within the section . The unit is locally cemented with dol omite. T. IS.HI. R.BOW. Unit 6 varies in thi ck ness from 0.9 to 3.2 m (3 to 10.5 ft), and averages 2 m (8 ft). Porosities range from 1.1 to 13.8 percent, Figure 7: Isopach map showing the distribution of lithofacies un it 3, the produc in g averaging 5.5 percent. Permeabilities range from <0.0 I to 97 md. sandstone, throughout nOrlh westem North Dakota . Contour interval is t m (3 ft) . Dashed tines are townships and are to km (6 mil on a side. Lithofacies Unit 7 is a medium to light grey, mass ive to wispy laminated siltstone. Locally, the unit becomes greenish-grey cemented with calcite. Dolomite cement is present ov er a where the argillaceous content increases and is generally restricted interval in two cores. Brachiopods occur throughout and include Chonetes gregarious, Chonetes ornatus, and Composila. Cores from we ll s in the central portion of the basin also include !! A' ~o, .. bryozoan and crinoid fragments. Many of the fossils are partially ~--'=-:-r-:-r-"7tr'or---=====:Er·;;,,;··-,-,"-' BAKKi~':~:~li~3- ~~o~~: ~£'.48ER or completely replaced with pyrite. NORTH DAKOTA Thin beds of tan to light grey, very fine-grained sa nd stone occur toward the bottom of unit 7 and are commonly rip ple cross­ lami nated. Beneath one of these cross -bed sets is an argillaceous la ye r, ri ch in brac hiopods. This layer was observed in several

EXPLAN ATI ON wel ls. o Unit 7 ran ges from 0.6 to 1.8 m (2 to 6 ft) in thickness. Permeabi lities range from <0.01 to 109 md . Porosities range from 0.02 to 12.8 percent. Accumulations of pyrite occur near the upper contact with the upper member. Bakken Formation: Upper Member The upper member of the Bakken Formation consists of an organic-rich, slightly calcareous, mass ive to fissile, dark brown­ Figure 5: Fence di agram showin g the corretati on of lithofacies units of the middle member of the Bakken Formation fro m Townships 153 to t59 N, NOrlh Dakota. The black to black shale. The alignment of calcite and/or pyrite grains lithofacies represented were described from cores. Oil shows are indicated over th e forms thi n wispy lami nations. Pyrite is disseminated throughout inlerval where present. but al so concentrated into lenses, nodules, and laminations. Small-scale fra ctures, observed in the lower member, are also present in the upper member. These fractures are filled with calcite and pyrite. Fossils observed within the shale include NENE SEC.9,T.157N., R.95W. abundant conodonts and rare brachiopods. TEXAKOTA ,INC. a HUNT OIL CO . HO.1SING NO. I The contac t between the middle member and uppe r member WEST TIOGA FIELD appears to be sharp and irregular or gradational. In wells where GR RES . the contact is sharp, a thin lag zone with pyrite and bitumen occ urs along the surface. The gradational contacts exhibit a gradual upward increase in argillaceous content.

Lodgepole Formot ion SOUTHWESTERN MANITOBA

upper member Three Forks Formation

un it :3 The Three Forks Formation is unconformably overlain by the Middle Member of the Bakken Formation throughout most of south western Manitoba. The Three Forks ge nerally cons i s t ~ 01' li gh t grey-green , bl oc ky or t11as sive, waxy, silty sltal e \\Itll - - - - t--'-"'=-"""'.t- g.... . di sse minated pyrile. It may also occllr at the Bakken conlaCl :lS :t en buff, ligh t grcy·gt·ecn or pu rpl e. si lt y, at'gill aceous dolostone: :1 purpl e, green an d brown varicoloured or t11oltled, tll:I "i\ c. ~l S h ~lk " I' fhree dolomitic shale; or as med ium ·grey, argi ll aceolls. si lly Fork s inl erb edded siltslone and sh ille. 11 is difficult 10 disli rlglli,h Fo rmo liDI'\ Bakken from Three Forks lith ologies in some areas.

Figur e 6: Typical log of Ihe Bakk ~1l Forrnalioll in NOrlh Dakol;\. The t hr~e infonTli ..d 13akken Formation: Middle Member member ~ of Ihe fonna! ion ;lrc i ndil"

south westcrn Manit oba. These faci cs arc correlative with tliose (7 ft ). The conlaCI of Llnit I with the Three Forks Formation is recogni ze d in Saskatchewan and North Dakola (Tablc I; Fig. 4). e rosional. as is ev id e nced b\' th e erosional brc cci" or C O I1 - Data we rc derivcd fr om Bakken core examined in 32 south­ glomerale at the b"se or unit I in seve ral of the cores examined . wes tcrn :vLtnitob~1 wcll s. Thc foul' lithofacies, in Jscending order, are id cntified as I'ollows: Lithofaci es Unit 2 is an illierbedded sequence of buff, li ght gre y, Ian or occasionally "salt and pepper", very fin e- to fine ­ Lithofacies Unit I is a buff to light grey or tan , very fin e- to grained, silty sandstone and lam ina e of medium grey or green, fin c-grained sandstone. The unit may be massive to friabl e, silty shale. II is ve ry thinly, parallel-laminated or thinly, wavy slightly wavy bedded, or thinly laminated. Small-scale ripple bedded or slightly undul atory. The laminations are 0.5 to I cm cross-laminations are occasionally present near th e top. Low­ (0.2 to 0.4 in) in thickness. The sandstone is qu artzose, slightly angle cross-bedding is also present in some cores. Wavy bedding argillaceous, well sorted, angular to subrounded, and generally occurs as 0.5 to I cm (0. 2 to 0.4 in) thick len ses. Laminae cemented wilh dolomite. generally consist of dark grey shale or green shale. Green shale laminae are often concentrated near the lower contact with the Palchy oil staining was noted in many cores. The facies Three Forks Formation. The sandstone is wellsorted, subangular exhibits fair to poor (5 to J 0 percent), intergranular porosity. to subrounded, and consists predominantly of quartz. The facies Burrowing is minor. The unit is mottled in places . Convoluted exhibits some fair to good (10 to 15 percent), visible, intergranular bedding (soft sediment deformation) is also locally present. One porosity and is often oil stained (spotty, patchy, or an even light well, at 6-7-4-21 WPM, grades to an interbedded grey-green, stain). It is considered to be a good reservoir facies. mottled , dolomitic shale, and mottled, dolomitic, argillaceous siltstone. In two wells in the Daly field (Townships 8 to 10; Ranges 27 to 29 WPM), unit I grades locally near its base to an interbedded Erosional contacts were noted within the unit in core at: 4-29- sandstone and red, dolomitic, silty shale (Fig. 8). It grades entirely 15-26 WPM and 14-35-16-27 WPM (Fig. 9). The 4-29-15-26 to a conglomerate in 4-29-10-29 WPM, and into an interbedded WPM well has a 10 cm (4 in) thick erosional contact near th e siltstone and shale north of Daly field in wells at 4-29-15-26 middle of the unit that consists of brick red, ve ry fine-grained WPM, 8-8-16-27 WPM , 11-9-16-27 WPM and 14-35- 16-27 sandstone intraclasts . This conl ac t can be Iraced 10 the 14-35-16- WPM. 27 WPM well. where it is present near the base of the unit. The contact is underlain by a 20 cm (8 in) thick, conglomeratic and brecciated zone ch aracterized by desiccation cracks and sandstone BAKK EN FORMATION - MIDDLE MEMBER intraclasts that range in size from 3 to 8 cm (1 .2 to 3 in). Small­ OALY FIELD ARE A M ANITOBA scale ripple cross-laminations were noted at the top of the unit in the we ll at 5-28-10-29 WPM. Unit 2 is entirely conglomeratic in 4-29-10-29 WPM and comprises green-grey shale intraclasts and silty, dolostone stringers.

BAKKEN FORMATION - M DOLE MEMBER TOWN SHI PS 15 AND 16 M A.N I TOB A B'

_ , oc ,,:: ~ ~ A P : ~

- - . - . ! - . • - .. ; -. - ~ ':! C,· = :-_ :. ;__ : ~ o-:...... , • : . . : :-. . 1;" - . A.21 WI· - ( XPLAN A fIO:i ~ ( (JIIQ .. t, ..... 0 ... ' ~.,~If J) .Ofh " ~ .. -"'.,.....,." ',.,,... 0 .,"'~j) LOC ro.1 -- ~i..~ 0 ,\,14·c.,.., ,, Figure 9: Fence diagram sh owing th e di stributi on of [h e lithofaci es unit s of the ".'(10'l'1li9(1" , ~ .. l " Middle Member of th e Bakken Form alion in T ownship, 15 and 16. M anitoba. 'UOO"",.v'l (ijj~1) : .. t ..,at't ••• :::-.: . {0 -- ~=~.!t~ Lithofacies r e prCSCIl ( l~ J arc dl! sc ri bed from cores. SeJimen! ary fe i:1!ure.<." ,1S well. as <-. oil siai ning are indi ca tcd .

Fi gure 8; Fencl.: di ag ram show in g the di stributi on of Ill '.! lith ofacies uni ts of the ,'vtiddl e M ember of Ihe Bakkell Formation in the Dal y field are a of Manitoba. Unit 2 is present in all cores examined and ranges in thickness Lithofacies ft..: prcc;enlcd arc des cr ibed from co rcs. SL'd illlcnl ary fea ture ~. a~ well as oil from 0.6 to 1.8 m (2 to 6 fl) averaging J. 2 rn (4 ft ). 'i (Ji ning al c IIlJi c;.ucd Lilhofacies Unil 3 is a buff to lig hl grey, or grey-green. very fin e-grained to silty , a rgillaceous sandslone or siltslone , Unit I is prese nt wh ere the Middl e Member is thickest. It inlerbedded wilh medium grey, silly shale. Th e sandstone and appears to have been deposiled as massiv e beds in min or erosional silt slone occur as di sconlinuous lenses or faint wavy bedding. or to pographic lows on th e underlying De voni an surface. Grains are predomin antly quartz and generally ce lll cni ed by Thickness r ~ n ge s from 0.7 m to 4 m (2 10 13 1'1) and averages 2 m dolomile. The shal e form s thin larninalions or partings. SIXTH INTERNATIONAL WILLISTON BASIN SYMPOSIUM 83

The unit may cont ai n bra c hiopods throuc.hout and is unit Irom tile underlying massive s lltstonc. The upper and lower commonly burrowed. Pyrite is prescnt in minor nm~un t s. Mottled contacts arc gradational in th e western portion of the s tud y are,\. in places, the unit changes late rall y to a si lt y, argi llaccous The upper contact is unconformable where B2 has channelled into dolostone or limestone in Township 8, Range 28 WPM and in th e B I. The unit is fossiliferous and dolomitic , becoming calcareolls Daly field area. Unit 3 is present in all cores examined except with depth. Disseminated pyrite is present. Unit B I ranges from 6-2 1- 1- 19 WPM and thickness ranges from OJ to 2.7 m ( I to 9 ft) 1.6 to 14.5 m (5 to 48 ft) in thickness. and averages 0.8 m (3 ft). Lithofac ies Unit B2 is a buff to cream, or greenish-tinted, Lithofacies Unit 4 is a m ass ive, light to medium grey, calcareous sandstone which consists predominantly of quartz with dolomitic, shaly siltstone to silty shale. It is generally burrowed minor feldspar and heavy minerals including disseminated pyrite. and present in all but seven of the cores examined. Brachiopods It may contain brachiopods and is slightly bioturbated. Numerous occur in distinctive zones or scattered throughout the unit in diastems are present. several cores. Fossil fragments are also a minor component. Thickness ranges from 0.3 to 2 m ( [ to 7 ft) and averages I m Unit B2 displays a tripartite subdivision. The lower portion is a (3 ft). The contact with the overlying shale of the Upper Member wavy and flaser bedded, silty sandstone and is transitional with is general\y sharp. the underlying unit B I. Shale clasts, up to 4 cm (2 in) in diameter, and felsic pebbles are found in channel lags where unit B2 Bakken Formation: Upper Member overlies the lower Bakken shale member in the eastern portion of the study area. The middle portion is a coarse-grained, sometimes The contact between the Middle and Upper Member is friable sandstone, and is transitional from the lower portion except generally sharp. The Upper Member is a black, massive, non­ where channelling occurs. This sandstone may be massive and/or calcareous shale, occaSionally fissile or finely banded in places. It may also have a basal, medium grey clay layer that reaches a bedded. Types o f bedding include: trough a nd tabular cross­ maximum thickness of 15 cm (6 in). The Upper Member changes bedding; horizontal and inclined bedding (up to 25 degrees); and in colour from a black shale to a purple, brown, or brownish-red swash cross-stratification. The upper portion is a wavy- and shale in the northern portion of the study area and the eastern half flaser-bedded si lt y sandstone and is transitional with the middle of Daly field. In these areas, the Middle Member is also oxidized, portion. The upper contact with lithofacies unit B3 is gradational. reflecting a period of post-Mississippian/pre-Jurassic subaerial The B2 unit varies in thickness from 0.4 to 15.6 m (I to 5 1ft).

exposure (McCabe, 1959). A· SOUTHEASTERN SASKATCHEWAN Five lithofacies were identified in southeastern Saskatchewan based on the examination and correlation of 35 cores. The ...... =_., - e subdivisions are based on Christopher (1961), who divided the middle Bakken sandstone member into two units, A and B. Unit B was further subdivided into B I, B2, B3, and B4. For the purpose ~ of this study, Christopher' s unit B4 has been renamed as unit C : (Table 1). The fence diagram in figure 4 and the structural cross­ ..... ,. ~""'~ o sections of the Bakken pools (Figs. 10, II , and 12) correlate these fPOQ0.4 ...... t-. 0 1.01 """ _ -.- facies on a regional and local basis. _ .....0.1 ...... ROCANvILLE BAKKEN SAND POOL , - SASK ATCHE WAN All three members of the Bakken Formation are present in the •! ; i i / 'ij • )' .~"" ~ ~ Saskatchewan portion of the study area; however only the middle Bakken sandstone member was examined in core. The lithofacies Figure 10: Structurat cross-section showing th e distribulion of lithofacies units of this member are described, in ascending order, as follows: across Rocanvi tte field, Saskalchewan. Lilhotogies represented were described from core. Bakken Formation: Middle Sandstone Member Lithofacies Unit A consists generally of a massive, dense, mouled, grey-green s iltstone. It is locally argillaceous, highly

fos s ilifero us, very calcareous, with pyrite disse minated A' throughout. The random orientation of the fossils suggests rapid burial. The basal contact with the lower Bakken shale member is either characterized by scours filled with fossil debris and pebble lags (shale clasts) or by contacts that appear to be gradati.onal. The gradational contacts may be related to the reworking and incorporation of unconsolidated lower Bakken muds into the si l.ts of the middle Bakken sandstone member (Christopher, 1961). 1- ' , , Load and flame structures with associated cross-bedding and fai nt ~ . horizontal laminae have been identified in se veral cores. The upper contact with litho fa cies B I is gradational except in the eastern shelf area. In this area, erosion has progressively truncated unit A and the lower Bakken shale me mbe r (Fig. 4 ). The unit RON eOTT 8"1(1([:-1 SAND fIOOL SA.SX A.TtllCW.\H ranges in thickness from 0 to 8.3 m (0 to 27 ft). : I : i U~ · · Lithofacies Unit B I consists of parallel interbeds o f dark grey • r I ! ! .- shale and buff, o r occasiona lly grey-green, silty sand stone. The Figure 11 : StruclUral cros~- s ec tion showing th e distribution o f lilho r

HUMMINGBIRD BAKK EN SA ND POOL A SAS KAT CHEWAN the middle meill ber is not entin'lv transgressive . Thrashe r ( 1985) Iio\'~ .. WAU.Hl studi ed the macrofossil s and biost ratigraphy o f Ih e Bakken. In his CDJoIttl'PoUJlI l't, 0 slUdy, th e middle membe r was divided into three biostratigraphic H'lIro-Aa.IIII11I£INJo I. [I lOCl(\f"\ - ~­ un it s (T a ble I ) He suggested th at unit I , eq ui va lent to

" .I.O<<marine transgression. shale and buff, slightly bioturbated , silty sandstone. The unit is Load structures, pebble and fossi l-ri ch lags at th e contact with the calcareous. It contains disseminated pyrite and vertical burrows. underlying shale. combined with random ly orie nted fossils, Load and fl ame structures occur at the base of the sandy laminae. sugges t ra pid burial as the s horeline advance d eas tward, [n the Roncott area (Towns hi ps 5 and 6; Range 25 W2M) unit B3 incorporating sediments and di spersing them deeper into the is punctuated by storm-generated density current deposits up to basin. The erosion of unit A in areas more proximal to th e basin 10 cm thick with what are recognized as the BC(D)E structural margin (Fig. 4), makes it difficult 10 determine the mechanism of di visions of the Bouma sequence. Thickness of B3 ranges from 1 to 4.5 m (3 to 15 ft ). deposition in the deeper basi n, where unit A is preserved. Lithofacies Unit C is a g rey-green, massive, dense, mottled, In Saskatchewan, subsequent shallowing of the water allowed dolomitic, a rg illaceous s ilts to ne. It is fossiliferous, s lightly the development of tidal flats and a ssociated tidal channels , bioturbated and contains disseminated pyrite. The basal contact is which, when factors s uch as structure , sedimentology and selected either on a massive, mottled s iltstone, or where s ilty migration are favorable, form the reservoir. A regress ive­ rhythmites are encountered. The silty rhythmites range up to 15 transgressive pulse resu lted in the deposition of units B I, B2, and cm (6 in) in thickness and are distingui shed from B3 rhythmites B3. Figure 4 shows B2 as a wedge-shaped unit which interfingers by their finer grain size and the presence of scattered fossils. One with unils B I and B3, until it is no longer recognizable in the core contained a 6 cm (2 in) thick band of fossil -debris. The upper deeper parts of the basin. The regression al lowed the shoreline to contact with the upper Bakken shale member is generally sharp prograde inlo the basin, depositing the coarse clastic unit B2, in and conformable. the nearshore environment. The finer-grained sediments of B I represent the distal equivalent of B2. Subsequent transgression DEPOSITIONAL HISTORY OF THE BAKKEN caused the shoreline to move lowards the marg in of the basin. FORMATION - MIDDLE MEMBER Unit B3 represents the distal eq uivalent of B2 during this Sandberg el 01. (1983) deve lo ped a depositional model for the transgressive phase. rocks of Middle Devonian through Late Mississippian age in the The interbedded laminae of B I (see Table I for North Dakota Western Interior. This mode l is based on e us tatic sea level and Manitoba equivalents) are genera lly highly bioturbated, changes. Based on their model, initial sedime ntation of the lower sugges ting s low sedimenlalion in a shallow s iliciclas ti c sea Bakken shales resulted from a rapid transgression in conjunction (Johnson, 1978). These laminae are transi tional to the sands of with tectonic activity of the Antler and Acadian orogenic be lt s. unit B2 (Table I l. which are typically flaser- to wavy-bedded, Evidence for this rapid transgression is the sharp disconformity of reflecting conslan tl y fluctuat ing, but re lativel y low-energy the Three Forks-Bakken contact along the basin margin. T his conditions in a n intertid a l fl at e nvironment ( Elliot, 1978). indicates that the Three Forks was exposed to erosion before sha le Elutriation may account for the m assive s ands o f B2. Tidal deposit ion. Furthe r evidence from cores inc ludes sharp contacts channe ls inlersecting the lida l fl als are more prevalent in th e with rip-ups and othe r erosional features. Rocanvill e area of Saskatc hewan, as is swas h cross-stratification, The initia l phase of black shale de position appears to have whi ch indicates a beach de posit (Harm s CI 01., 19R2). 111 th is mea, occurred in a shallow sea, based on the presence o f benthi c fauna the B2 sands re st unconformabl y on the lower Bakken s hale in th e basal port ion of the lo we r shale membe r. Paleontological member or th e Torquay Formation. a nd geochemical data indicate a progressively dee pening sea due The B2 sands in the Rocanvill e (Townships 15 and 16; Range to on-going transgression. Depth of lhe water column is still in 31 WIM ) area of Saska tc he wan , which a re proximal to the deba te . A si ra tifi cd water c olumn with a n a erob ic bottom margin of the bas in. are vCl"y coarse and friable, with I'cl atively conditions developed wit h this deepening event. good porosit y al:ci pe rmeabili ty . In contrast, th e porosity and The middle member of th e Bakken Forma tion is gene ra lly permeability of t h ~sc sands in the Roncott (Townships 5 and 6; consid ered to be a tra nsgressive deposit, b: iS.::d on it s onlapping Range 25 W2M and Hu mmingbi rd (Towilship 2; Range 19 W2M) relalionshi p wi th the underlyi ng unil s (Webster, 1982: 1 984~ areas, which arc much farlher from th e basin m:lrgin. are much Hester and Schmoker. 1985). However, recent data indicates that less. SIXTH INTERNATIONAL WILLISTON BASIN SYMPOSIUM 85

Unit BJ (Table I) is simi lar in litho logy to B I. The units syncline whi ch li es along the Birdtail-Waskada ax is. The lallcr is merge in the wcstL:rn and southern ponion of the basin (Fig. 4). it north-trending zone, approximately 32 km (20 mil east of th e The B3 unit is s li ghtly to moderately bioturbated w ith vertical Saskatchewan border, along whi ch numerous local structure and burrows, suggesting a s low rate of sedimentation, in contrast to isopach anom~li es in the Devonian and later stra ta arc the slightly faster rate of sedimentation represented by the lower concentrated. These anomalies may be a direct or indirect result of portion of B I, which is intensely bioturbated. The density current salt di ssolution resulting from minor tectonic movement along the deposits interbedded with the deeper water shales of the 8 3 unit in bo undary zone between the Churchill and Superior provinces the Roncott area are probably stonn-generated. Walker (1979, p. (Trans-Hudson orogenic belt) (McCabe, 1966; Green el al. , 1985) . 94) stated: "The presence of rare "turbidites" would indicate the The axis coincides with the crustal boundary and the present possibility of density current activity, and would not condemn the solution edge of the Prairie Formation salt section (McCabe, entire sequences to deposition in great depths of water." 1966). The anomalies have been important in controlling the accumulation of oil in the Daly, Virden, and Waskada (Townships Unit C (Table I) is quite thin but widespread throughout the 1 and 2; Ranges 25 to 27 WPM) producing areas of southwestern basin (Fig. 4). Currents active during the deposition of this unit Manitoba (McCabe, 1963). were stronger than those occurring during the previous unit. Disarticulated brachiopods present are sorted by s ize and Within the Daly field itself, several minor structural highs are concentrated into thin, well-sorted beds of grey siltstones and very coincident with areas of Bakken production. Within the Waskada fine-grained sandstones. field area a minor south-southwest plunging structural nose is coincident with anomalous Bakken and Three Forks thickening. A major eustatic rise in sea level related to further large-scale movement associated with the Antler and Acadian orogenic belt The Saskatchewan portion of the study area is divided by the and onlap of the black shale sea followed deposition of the middle Elbow-Hummingbird monoclinal flexure into two structural member (Sandberg el al., (983). This sea level rise represents the provinces (Christopher, 196 I). These provinces are defined by the high stand of the Bakken seas. presence or absence of Middle Devonian evaporite beds (Fig. 14). The evaporites terminate along a northwesterly trend whic h The depositional hi story of the basin is further complicated by approxi mately coincides with the Elbow-Hummingbird flexure. the dissolution of salt in the Devonian evaporites. This collapse The eastern s ide forms an e asterly striking monocline with and associated features can be documented in North Dakota, associated subsidiary anticl inal and synclinal structures (including Manitoba, Saskatchewan , and Montana (McCabe,1959; the syncline that underlies the Rocanville field). Devonian Christopher, 1961; Anderson and Hunt, 1964; Webster, 1982; evaporites underlie the eastern portion. The western side has an 1984; Martiniuk, J988) . irregular surface with easterly and no rtheasterly trends. The evaporites are a bsent from the western s ide. The Elbow­ STRUCTURE Hummingbird monoclinal flexure forms the eastern limb of the Hummingbird synclinorium in the southernmost portion of the A structure map constructed on the Bakken Formation for the study area. study area is shown on figure 13. In North Dakota the Nesson anticline is the most prominent structural feature. This anticline Adjacent to the Hummingbird synclinorium is the Roncoll trends north for 176 km (110 mil from the KiJldeer Mountains, anticlinorium. This is a broad, 48 km (30 mil wide fold plunging Dunn County, to just south of the Canadian border (Fig. (4). in a south-southeasterly direction. The structure exists due to the Associated with the Nesson anticline is the western Nesson fault, presence of an outlier of Devonian evaporites. Overlying a feature that extends for the length of the fold, and the northwest­ sediments are draped over the outlier, forming the feature. trending Antelope anticline. The northeast side of the Antelope structure is also faulted along its length. Episodic movement along Other notable features include the Rocanville-Torquay trend, the western Nesson fault and the development of the Nesson the Regina- Melville platform, and the Herald and Torquay anticline has been related to basement tectonics (Gerhard el 01., embayments (Christopher, 1961). The Rocanville-Torquay trend 1982; 1987; LeFever el 01., 1987). consists of a northeast-trending series of depressions outlined by producing wells (Fig. 14). The Reg ina-Melville platform In the north-central portion of North Dakota, another basement represents "a broad undifferentiated sedimentary area between feature that influenced the deposition of the overlying units is the more basinal localities to the north and south" (Christopher, 1961. fault that separates the Superior craton from the Trans-Hudson orogenic belt (previously referred to as the Churchill craton or Precambrian province) (Green el 01., (985). Movement of fluids along this fault zone is apparently responsible for the dissolution of salt from the overlying Prairie Formation (Devonian). Evidence for this dissolution can be observed on structure and isopach maps of the fom1ations overlying the Prairie.

Minor southwest-plunging folds are present in Burke County (Townships 161 to 164 N; Ranges 89 to 93 W) (Fig. 15). These fo lds probably result from basin subsidence, and have had an effect on the depositional palterns of the individual lithofacies, and as well porosity and permeability within the lithofa cies.

In Manitoba. structure on the Upper Member is fairly regu lar and follows the regional Palcozoic tilt. dipping southwest at an average or 6 m/km (32 ft/mile) (Fig. 13). Several features depart from the regional pallern. The Virdcn (Townships 9 to I I: RRnges figure 13: S[ru c [ur~ m:lp on [he tOP or [h e B: !h:k en FOrrll ;l\ioll. (untoll!' interval j" 25 to 27 WPM) and Daly (Townsh ips 8 to 10; Ranges 27 to 29 100 m 028 fll. IJa'\hctl line In nOnhC;l.SICrn M;Jn ilU oC! j" the cro:;iun:iI Ji llli l of Illl: WPM) field s arc separated by a prominent north-south trending 8akken f7onnatlon . 86 SIXTH INTERNATIONAL WILLISTON BA SIN SYMPOSIUM

p. )SJ) Thc He l'ald and Torquay embaymcills re presenl lhe di ssolution of thc unde rlying De vonian Prairic s,ill and SLl h t~ qucnl expl\~s ., i()1l of the Willislon Basin in soulhern Saskatchewan. c ollapse . Isopach m a ps of all three m e mbers . as well as underlying and overlying formations. display abrupt thickness ISOPACHS changes. This is further supported by isolated occurrences of th e lower member throughout north-central North Dakota. Distribution of the middle member of the Bakken Formation throughout the study area is shown in figure 16. In North Dakota Examination of an isopach map constructed for the middle the Bakken isopachs show depositional patterns related [0 the Elk member sandstone, unit 3, shows thinning over pre-exis ting Point Basin sedimentation. The depocenter of the middle member structural features. such as the Nesson anticline and a series of is elongated north-south and is located just to the east of the folds in Burke County (Fig. 7). This is supported by the Nesson anticline. This is similar to isopach maps of the lower examination of available cores. The isopach of unit 3 also shows member. However. these trends are not apparent in the upper that its distribution is not as extensive as the distribution of the member, which has a poorly defined depocenter. The middle entire middle member which continues south of the study area. member, from its maximum thickness of 27 m (87 ft), thins In Manitoba. the isopach trends of the Bakken Formation are gradually away from the depocenter towards its depositional limit. generally northwest-southeast, reflecting deposition related to the Abrupt thickening and thinning of the middle member in the Elk Point Basin (Fig. 2). The most significant changes in nOrlh-central portion of North Dakota are probably related to the thickness of the Bakken occur within the middle member, which

ROCANVILLE

/ / 710m aew 3m OCM •• / 6mOCMe 73m~ IZmOC/

/ 14mOCM 37m OeM I 9mOCM. /2~mG.OC M • 14 0 JII G.OCM 3mG~OCM / • ~. DALY8mSOCM RONCOTT FIELD POOL c 34.....m O.W CM "07(5/ / 12mGCM ~ ~ 9mCloil • B2mG.OCM 6O.oeM ;. a • ~S2m O.MeW. /

35m OeM ~ o ~~:g~ :::E .. ~mo'w/ o "' II> ~",G. oCM' 6m OCM 29 O.WCM ..... 25m G. ),IICO__ ...._ • I f----.~ • 9OmG.OCM L Saskatchewan Monitobo North Dakota o / ( pr",rie)r­ • \501/ )0111/18( (' ( J Edge 01 I prair ;eso"l I I EXPLANATION ~ ESTABLISHED BAKKEN OIL POOLS ~ MISC . BAKKEN PRODUCING AREAS A SINGLE BAKKEN OIL WELLS

OIL SHOW ON D.S.T. •o GAS CUT D.S.T. • OIL SHOW IN CORE OR SAMPLES

figure L-I: Di;tgr:1111 "hawing [ilL' Il' l;ui o Il Ship of structural fI..! ;.lIun:~ to oil shows and oil producti oll within the stud y area. Major oilfields producing fro m Ih e middle Ill elllbo.!r or [he Bdkkcll r Ofl llaliorl . oil ... hows from drill :-ole m tests, COf t,!S or s:l lll plcs, and gas sh ows :'Ire i fid iclIl.! d. Limit of [h e Pra iri e FOf1l1

Only olle well (NENE Sec. 9, T.157N .. R.95W.) has a lengthy Temple rield BakL'n pool (Township 158 N: Ranges 95 and pl'(Hlu ction history. COlllple ted in February 1976. the well has a 96 W) consists or (\\' 0 well s which were drilled in 19S<). The cumulative production of 11,669 m ' (73,400 bbls). This well was initial recompletion was unsuccessful with low oil-high water stimulated with two acid tr'eatment s (4,000 gallons of IS percent production and was plugged and abandoned eight months later. IICI) and a gelled water/sand fracture treatment. The next well was This well was perforated in the lower Lodgepole Forlllation, not completed in 1987 and was acidized with 500 gallons of acid. the Bakken. The second well was perforated in the upper sha le to the base of the sandstone, unit 3. Reservoir data for thi s well are Other Fields presented in Table 2. Production in the remaining fields is restricted to one or two The Bakken pools in the remaining fields consist of one well wells. These wells are responsible for the remaining 34,976 m' each. Perforated intervals cover the upper shale to the base of the (219,998 bbls) of oil produced from the middle member of the sandstone or at least the middle member. All of the wells were Bakken Formation. s timulated with an acid and/or fracture treatment. Limited production was yielded by most of the pools with the exception of The Bakken pool in North Tioga (Townships 159 and 160 N; the wells in Sauk (Townships 159 N; Range 95 W) and McGregor Ranges 94 and 95 W) consists of two wells with a cumulative (Townships 158 and 159 N; Range 95 W) fields. production of 6,929 m' (43,585 bbls). The earliest well, completed in 1987, perforated the entire Bakken interval. Perforations in the SOUTHWESTERN MANITOBA second well, completed in 1988, are restricted to unit 3. Both wells Daly Field were stimulated with a sand-oil fracture treatment. Production was first established in southwestern Manitoba in the Daly field in 1985, fo llowing the Newscope Resources EXPLANATtON Limited discovery at 13-21- 10-29 WPM. The well was completed .. PRQDUC lt,G fl EL O­ ~ B':'KKE~ POOl in the Middle Member with 2 m (7 ft) of net pay. Prior to the Bakken discovery , the Daly field was productive only in the \:) PROc:..:C ING fiElD Lodgepole Formation. Bakken and Lodgepole production is presently commingled in several wells. Bakken oil in southwestern Manitoba is 824 g/m" (40.2 0 A.P.!') and has a sulphur content of 1.30 g/kg. The shallow depth to production and high quality of oil make the prospect for LOCATION MAP Bakken in Manitoba attractive. Average depth to the produci ng zones of the Middle Member is 874 m (2,867 ft). Seven Bakken pools have been established in the Daly field since the initial discovery: A, B, C, D,.E, G and H (Fig. 18). In total , 35 wells were active Bakken producers as of January, 1991. As of December 31, 1990, the Bakken had produced 83,700 m .l

o 40mi (526,473 bbls) of oiL Figures 19 and 20 summarize cumulative o 5 10 15m. I-----.' and average daily Bakken production for the Daly field. I I i I I ! o 60km 10 20 km Proven remaining established reserves for the Bakken in the Figure 17: Map showing Ihe dislribulion of producing oil fields along Ihe non hem Daly field as of December 31, 1990, were 43,200 m' (271,728 Nesson anlicline. Fields producing from Ihe middle member of Ihe Bakken bbls)( 1990 Manitoba Energy and Mines reserves estimates). Formalion are indicaled in btack. Reservoir properties described for the three multi-well Bakken pools in the Daly field (A, B and D) are given in Table 3. Table 2: Reservoir properties for North Dakola oit fietds producing from Ihe sandslone. unil 3. wilhin Ihe middle member of Ihe Bakken Formalion. Bakken oil reservoirs within the Daly field appear to be controlled primarily by stratigraphic factors. They are localized Temple North Tioga Stoney ie ... within paleotopographic lows of the underlying Devonian Sp£tC ing Uni l 160 320 320 erosional surface, where the sandstones are thickest. No. of Produc i ng Wells Unit I is the primary reservoir facies of the middle member Average Net Pill' (ft) 12 12 .5 and the one in which there are the majority of completions. Based

Av e rage Porosity (X) 2. J 12 on core analyses, porosities range from approx.imately 15 - 20 percent within the unit. Oil shows have also been noted in unit 2, AVeral:l' "taler SAturat.ion (X)( 5.·1 80 l:i 21 although, permeabilitie:s are generally lower within thi s fa cies due to more silt and fin ely argillaceous laminae . Oil Grav i ty, API @ 60" .10 39. 4·1. 0

Rcuc r vo i r Pr I VI;:: The distribution of unit I is related to the paleotopography or Mt.:dt(l n i Bm SOl llt. i OIl Gas 9 00tH !. J ~ )11 (;;:\5/ Solution Gas the underlying Three Forks Formation. It is present and a potential F l u 1([ Dr i ve reservoir in the Daly Field where it has infilled minor eros ion:" Vol um e trics . OU I P, bill !; 139,000 ·172,79B 1, 765,000' lows on the underlying Devonian erosional surface.

J{t• .' covcrllble Oi 1 1·1,000 ~ i • 279 26-1, 7C~ ' Stratigraphic trapping within the middle member in Daly field

Re cove ry t uCl iJ r (% ) 10 10 IS is c reated by the latera l pinc hout and variation or unit I in combination with an up \Vard fining to the very fine-grained. fine ly Cu. uhti v ~ Prodvc;:l. ion Oil ( 12/1 990 ) ,1, (i(j l ..j J , ,"'iB :, 213, SRO laminated sandstone of unit 2. Wnt e r ( 12/1990) 1, 70.1 ::' , 1,0 12.1 98 The rence diagram (Fig. 8) shows the productivc facie s within ·Yl,)lu m!~tri C ~ .... !'C' ('Ii.I!;U] ,\I r:d r O I' II ~ lin c.:l rl~; tluit. ur IGO i1.('t'~ S , i ll'.telld of tli (' (ll; s : ~~ l lI'd :1 21J (1(' ('( ' ! " J!II (" II I ~ , the middle member in th e Daly Field. In the Bakken A Pool it is SIXTH INTERNATIONAL WILLISTON BASIN SYMPOSIUM

diffi cull to di stinguish the lilh ology of unil I fl"Olll Ihat of th e lalllin.lIi ons ncar the [1.IS':. anci unil :1 lilh()I( )~ y rr ()tl1 ,I vcry I'itlc­ und c rlying Three Forks Fo rmati o n. The lowe r co ntac t is grained, mOlll eci s'lIlci ston.: to an arg i 11 .!Ccoll '. si II y dolostone'. questionable in the wells at 10-2 1-10-29 WPM , 4-28-10-29 WPM The lithology or the B,lkken B Pool is sil11ila!' to the Bakken A and 5-28-10-29 WPM. However, unit I is interpreted in th ese Pool; however, al l or most or the unils in the middl e mel11ber arc wells to hav e changed laterally in it s lower portion, into an hematite-red, which indicate th at these units hav e undcrgone interbedded, siltstone and blocky, green shale or marl. This has limited the eastern extent of the reservoir by creat ing vertical and oxidati on or exposure that appears to have occurred less lateral permeabi Iity barriers. extensively elsewhere in the Daly fiel d area . The western limit of the Bakken A pool is defined by the well Structural factors are of secondary importance in the at 4-29-10-29 WPM, where both units I and 2 are completely accumulation of Bakken oil in the Daly field. Minor structural conglomeratic. The northwestern limit of the pool is undefined closure is evident on highs on the upper member at the Bakken B and offers potential for future development. Pool. Minor structural hi ghs or noses on Ihe upper member are also noted at the Bakken A, C and D Pools (Fig. 13). The Bakken D Pool , as represented by the well at 9- 14-10-29 WPM, shows several lateral changes in units 1,2 and 3 from the It should be noted that a potential reservoir also exists below wells at the Bakken A Pool. Unit I has changed from a marly, the Devonian erosional surface within a vuggy dolostone. The unit interbedded, very fine-grained sandstone and shale to a very fine­ was perforated along with unit 1 in th e productive Newscope to fine-grained , banded sandstone. Unit 2 has changed to a very Opinac Daly 11-21-10-29 WPM well. fine-grained, mottled, hematite-red sandstone with green, shale DALY FIELD - SOUTHWEST MANITOBA AVERAGE DAILY OIL PRODUCTION (BY YEAR)

MJ/OAY # WELl.S ~ -- 40 0 100 ~ . , t / 35

/ - 30 10 [ - 25 ~ t - 20 - 15 ~ 1 _ ~ 1--+-+--1-­ :: !. - 10

Production L D WellS I - 5

0.1 0 1956 1961 1966 1971 1976 1981 1986 1991 Figure 20: Average daily oil production by year for Daly ri (.' ld in SOU lh\\cSICrn Maniloba .

Table 3: Reservoir propenies for Ihe Bakken pools in Dal\" lIeld. ~1anitoba .

Daly Daly Dal y J3akken A Figure 18: Map showing the producing well s as of January 1991 i" Daly fietd. Pool Ba.kk en B Pool 8a,l.;ken D Pool Manitoba (Mar1iniuk. 1988). Area (ha) JJ6 2'0 2<0

No. of Produci ng \o'ells 15 12 CUMULATIVE BAKKEN PRODUCTION Average Net Pay (.1 1.6 1.8 2.0 DALY FIELD - SOUTHWEST MANITOBA Average Porosi ty (1) I . 16 "ni3x1000 WELLS # Average ~ ater 70 700 1r======~------~~~ Saturation (ll '5 54

TOTAL PRODUCT tON Shrinkage Facto r ! fro I 0.89 0 . 89 0 . 89 60 D WELLS Ori ginal Oil-in-Place (10:1.3 ) 11 2.1.2 491.0 500 - 50 Recove rab le RC'se rves (IOllI) I ci :.9 II .; Sl • 400 40 Primllry Reco ve ry } /I; (' IQ r (t) (soluLlon BI'I~ dd \'o.:) S.b 2, --' 300 30 CUlIIu lati vc Oi I II Product i on (IOJ.) t ;; .t H . .1 200 ~ 20 R e lJl~ i 11 i ng Re cover",b l c I tlescn "c s (10l . ) ) i 5 . 2 .1 ." t 100 - 10

'J. A p lloL .... (ti (' r r loud ~H · f)F ' r .... - IHI. ." b t'l.!'n r~~c,~(l 'I .:. JUL: of : " II I h .. -t " , ,':- o Poo l , injcC: luJrI c o .al:n(:e" n a~ !1I \ (' r",-' J ';wSPoJ l \I .. •• ,111 p :l Ll ~" :' . I 1 I ! ., ~.. , J o I I ,-'--'--'-t-'- '-f-! n:·/ Jul y, I 90 . loll ~ r rlOO d r c"pan·' '" , ", o b""p.·! 1 11 f' H t\ : , -: !-k.'l-w.' 1_- 0 19 5 6 1961 19 66 19 7 1 1976 19 8 1 1986 1991 July , J9!JO a nd FeOl'ull r r. 19!1 1, •.L t ll y fH-odu.: t I QII I IW I " :. frOG . .,; =:'-,-! lo 17. M a J/rl. Cua"ltlt ; \'(, ,· oid'!.{ ..... :- ,.td nr: <:> .... n · ltl '1 tU I iJrf! i ':31 fl o r}' e lH i .. 6 i;'S ( ,)1' "· hl,· :- ;' L:p

SOUTHEASTERN SASKATCHEWAN natural \V~lIer influx dri vc mechanism (Gillard and Jmdan, 19 84). Excellcnt rc se r\'oir perme abilit y "ould therdore account for th e Cumulalive Bakken oil production from s outh e ast moderate oil re covery. S~lskatchewan totalled 60 I ,232 m' (3.8 million bbls) at the end of 1989. Figure 21 indicates a sharp increase in yearly Bakken ROCANVILLE BAKKEN SAND POOL AVERAGE DAILY OIL PRODUCTION (BY YEAR) production beginning in 1985. A portion of this increase can be atlributed to an infill program at Rocanville. However, the M:)/DAY II WELLS 100 r------20 majority of the increase is due to the development of a new i 19 Bakken pool at Hummingbird as well as scattered Bakken , 18 discoveries throughout the area (Fig. 14). Economic production ~ 17 J 16 from the Bakken throughout southeastern Saskatchewan can now i 15 be found outside the traditional Bakken producing areas of 14 10 13 Roncott and Rocanville 12 11 CUMULATIVE BAKKEN PRODUCTION 10 SOUTHEAST SASKATCHEWAN ".~ 9 - 8 7 m3xl000 # 01 WELLS 6 700 r.:======~------~ 70 5 -- TOTAL PRODUCTION 4 600 0 WELLS 60 Production 3 ~r~l CJ Wells 2 500 50 r u,LU.J../.J..LI.. ..L IU-p 0.1 ~~UU~~~~~~~I ~ 1956 1961 1966 1971 1976 1981 1986 1991

400 40 Figure 22: Average daily o il productio n by yc"r (o r the Rocanvillc Bakken sand pool in Saskatchewan. 300 - 30 RoneoU Pool 200 20 Roncoll is the oldest producing Bakke n reservoir in - 10 southeastern Saskatchewan, and has produced s ince 1956 (Fig. 23). It has a cumulative production of 104,843 m' (659,462 bbls). iJJ.lliJlWljJ!WW.lIL.--+J 0 The pool may be near the end of its productive life with remaining 1961 1966 1971 1976 1981 1986 1991 reserves of onl y 11,000 m' (69,190 bbls) from initial reserves of Figure 21: Cumulalive production from the Bakken Forrnation in southeastern 116,000 m' (729,640 bbls). Original oil-in-place is calculated at Saskatchewan, 1.037 million m' (6.5 million bbls) (Saskatchewan Energy and Mines, 1989) with estimated recoveries of II percent. The virtues The majority of production originates in the medial B2 of infill drilling should be reviewed to detennine whether or not sandstone unit where permeabilities and porosities are the the capture of wedge andlor unswept oil is an economic option. greatest. However, oil staining has been noticed, and production The majority of the well s in the Roncott rese rvoir are has been attained, from silty intervals within the B I and B3 units. producing from the B2 unit, however, the perforated intervals of This is possible due to the interfingering nature of these three some wells have crossed over into either the B I unit and/or the B3 units (Christopher, 1961). The future potential for Bakken unit (Fig. 11). Examination of core from these wells shows oil production along this trend is enhanced by the occurrence of these staining in coarser-grained beds within these units. Penneabilities stratigraphic traps and provides new possibilities for exploration range from 0.75 md to 75 md, averaging 6 md. These beyond the areas of known structural traps. oermeabilities are extremely low compared to an average of Roeanville Pool RONCOTT BAKKEN SAND POOL Rocanville is the most prolific Bakken reservoir within AVERAGE DAILY OIL PRODUCTION (BY YEAR) southeastern Saskatchewan (Fig. 22). Cumulative production as of M3/DAY II WELLS October, 1990 reached 339,165 m' (2.1 million bbls). Remaining 100 ~------~~ 10 reserves are 102,000 m' (641,580 bbls) from initial reserves of 441,000 m' (2.8 million bbls) or 19 percent of original oil-in­ 9 place. The original oil-in-place as calculated by Saskatchewan 8 Energy and Mines (1989) is 2.326 million m' (14.6 million bbls). ' ~ ------4 The Rocanville reservoir is located entirely within the B2 unit of the midd Ie Bakken sandstone member where it exhibits typical channe l cross-bedding, f1a scr bedding andlor rhythmites (Fig. 10) r This lithology accounts for the excellent permeabilities in this rese rvoir which range from 30 md to as high as 1000 md with an average of 65 md. Permeability m ay have been enhanced by dolomitization of the original calcium carbonate cement (Kent, 19 84), The average net pay is 5.6 m (18 ftl. The average porosity =-:-'r­ is 20 percent (Saskatchewan Energy Mines. 1989), -I 1..1' , 0, 1 .,..,i :-<,-I--l.l.u.. . -----'- _ .....L... - -- Pressure Ilistory on this pool indicates that the reservoir oil was 1956 1961 1966 1971 highly undcrs~lturat e cl at original conditions and that the pool is Fignre 23: Average dail y o il produclion by year for Ihe Rnneo lt ~:b J...J... l·[\ ,' ,lI ld poo l III slI bject only to rock ancl liquid e xpansion along w ith a panial S ~ I'.;k al c h e wan. SIXTH INTERNATIONAL WILLISTON BASIN SYMPOSIUM 91

65 Illtl in tilC Rocanville reservoir. The difference reflects tile Fault zone and the Weldon Fault of northeastern rVlontalla interfingcring of units B 1, B2, and B3 along the distal margins of suggesting that thesc features may extend into southeastern the clastic wedge, while the proximal reservoir at Rocanville is Saskatchewan. composed entirely of B2. Net pay averages 4.5 m (15 ft) and POTENTIAL porosities average 14 percent. Porosity enhancement by dolomitization is more evident here than at Rocanville. North Dakota HUMMINGBIRD SAND POOL AVERAGE DAILY OIL PRODUCTION (BY YEAR) Potential exists for production from unit 3, within the middle member of the Bakken Formation in North Dakota. Core It WELLS 100 c-M3/DAY------, 10 examination shows that the depositional pattern of the lower lithofacies, units I through 5, were affected by pre-existing 9 structure and topography. Thinning of the sandstone, unit 3 over ~ 8 structural noses is evidenced by cores examined from Burke I County (Fig. 15). This relationship strongly suggests a potential 7 10 ~------1 for updip stratigraphic pinch-out of the sandstone unit against 6 impermeable rocks. When this situation is combined with a source rock, the Bakken shales, a potential for production is present. The sandstone unit is in contact with the upper Bakken shales of the study area. Fractures present locally also form other migration pathways. These factors can also be applied to other potentially productive lithofacies of the middle member. -2 A favorable property of the sandstone unit IS ItS response to Production _ Wells I stimulation. The sandstone unit reacts well to stimulation by acid

O.l ll- I I -- '--~ 'O and/or sand-oil fracture treatments that can greatly increase the 1956 1961 1966 1971 1976 1981 1986 1991 effective drainage area and enhance production. Figure 24: Average daily oil production by year for the Hummingbird Bakken sand Southwestern Manitoba pool in Saskatchewan. The Daly field has been developing continuously since Bakken Hummingbird Pool oil was discovered in 1985. The area has been attractive due to the high quality of Bakken oil and the prospect for uphole completion The newest pool of established Bakken production is on the in shallower zones within the overlying Lodgepole Formation. Hummingbird structure, where Birdbear and Ratcliffe production already exist. Bakken production at Hummingbird began in 1985 Most of the Bakken pools presently established in the Daly and rose dramatically over the next two years. Since 1987 a rather field have been defined. Potential for future Bakken development steep production decline has persisted (Fig. 24). remains however, in the northwestward extension of the Bakken A Pool into Township II, Range 29 WPM (Fig. 8) where unit I is Cumulative production is 60,210 m' (378,720 bbls) to October, present. 1990. This represents well over half of the initial reserves of 98,000 m' (616,420 bbls) and leaves only 38,000 m' (239,020 Eastward, in the Virden field (Townships 9 to II; Ranges 25 to bbls) remaining to be produced. Saskatchewan Energy and Mines 27 WPM), the Bakken remains largely untested. This is an area of (1989) has calculated original oil-in-place at 525,000 m' (3.3 Bakken thickening and of known salt collapse features within the million bbls) which places the recovery factor at 19 percent. shallower Lodgepole Formation. Possibility for a Bakken subcrop play may exist along the eastern edge of the field (Fig. 16). The majority of production is from the B2 unit (Fig. 12). There are also shows in the lowest portion of the B3 unit, where at Northward, toward the northeastern limit of the Bakken least two wells have been completed. A distal equivalent of the Formation, several free-oil recoveries have been made from drill producing channel sands at Rocanville, the Hummingbird stem tests in the middle member; specifically, from wells in reservoir has a higher argillaceous content. The sedimentary Townships 15 and 16, Range 27 WPM (Fig. 14). The locality structures that dominate the Hummingbird reservoir include features a Bakken structural nose (Fig. 13). Minor erosional f1aser-type bedding and wavy laminated sands and silts instead of breaks within units I and 2 and lateral lithologic changes from the channel cross-bedding present at Rocanville. Porosities and fine grained sandstone to argillaceous, laminated siltstone. offer permeabilities at Hummingbird are lower than the Rocanville potential for a stratigraphic trapping eastward of this area. reservoir. The average porosity and permeability at Hummingbird Several completions have been attempted but have not been is 9 percent (Saskatchewan Energy and Mines, 1989) and 5 md, successful due to high water recoveries. respectively. Average net pay is 4.9 m (16 ft). Southeastern Saskatchewan Miscellaneous Production The potential for exploration and new disco\'cric<; in Ihe Miscellaneous single wcll pmduction and undesignated small Bakken is immense. Oil shows throughout the Saskatche\\an pool production accounted for 114,335 m' (719,167 bbls) of the portion of the Williston Basin as well as scattered ,;ingk \\ell total Bakkcn production in southeastern Saskatchewan as of production along the Bakken production trend (Fig. 1-1) suggest December, 1989. The most significant production is from a small thai significant amounts of undiscovered Bal.. ;j.,en oil remain 10 be cluster of 12 wells in the North M idale area (Townships 6 and 7. found. Range I I W2M) that pmduced 56,599 111' (356,007 bbls). Bakken sourced oils are characterized by \erv lon(' mi~rati'l!1 The majority of this production is found within the Rocanville­ pathways (Osadetz 1'1 al.. Ihis volume). having h'ccn icner;tcd in Torquay structural trend (Fig. 14) (Christopher, 1961). The few the deepest pOl1ion or Ihe basin .. south of the i\\lssolJl'i Ri\er .. and exccptions to this rule ,\I'C found on trend with the Bmckton-Froid migrated radially as far away as Rocanville. o\er 200 kin (12-1 SIXTII INTER AT/ONAL WILLISTON BASIN SYMPOSIUM mil. The Ienglh of l11igr;lIioll may bc a factor in dClermining API gravity of the oil. Rocan vi ll e oil has a grilvity of 36° API whereas ..q ~ali led M I'}fOhOll ~ll'I wO y • 8o k ~fo Product ion Roncoll and Hummingbird produces 40° API oil. Even closer to \, ~ MGln" o~e Bok~ . 1\ HydracorbonGeneroriol'l th e source. the previously mentioned North Midale wells produce ~ BokkenE:r.pulsionThr eshold 41 ° API oil and are situated directly north of the Bakken ~ ~~~hu~;~':i;~O~n~~~~~' Plains hydrocarbon generation region as described by Osadetz ('/ al. (in \ review) (Fig. 25). Well s tested at Torquay and north of the / international border at Roche Percee had 43° and 45° API oil. re spectively. Structural features that aid and control entrapment of Bakken oil include the linear depressions associated with the Rocanville­ Torquay structural trend (Christopher. 1961), as well as the \ reversal of regional dip caused by flexure of the Bakken on the flanks of the Roncott high. These structures probably did not aid in the migration of oil from the center of the basin, but do provide WINNIPEG \ BAKKEN • favorable conditions for structural entrapment. SUBCROP \ The interfingering of the medial B2 sandstone wedge along MANI19_~A..-1 with the laminated shales and silts of the B I and B3 units, --.~ provides another avenue of entrapment in areas where structural features may not exist. \ SOURCE ROCK AND MIGRATION PATHS The Bakken Formation has been documented as an excellent petroleum source rock within the Willi ston Basin (Dow, 1974; Williams, 1974; Meissner. 1978; Webster, 1984; Hester and Schmoker, [985). The black shales are the richest and most widespread rocks in the Williston Basin (Osadetz and Snowdon, in review). The upper and lower shales of the Bakken Formation Figure 25: Diagram showing the area or mainstage hydrocarbon generation in [h e Bakken Formalion. The area where Ih e Bakken has exceeded ils expUlsion Ihreshold yield rich Type II sources (Dow. 1974; Webster, 1984; Osadetz is also indicated. as well as. tile generalized migration pathway (frolll Osadelz f! ! (1/ .. and Snowdon, in review). The upper shale is generally richer than 1991). that of the lower shale. erosional and paleotopographic lows on 'the underlying Devonian Osadetz and Snowdon (op. cil .) concluded that thermal surface, are coincident with productive areas in Saskatchewan and maturity of source rocks in the Williston Basin was strongly Manitoba. affected by elevated heat flows, notably along the Nesson crustal structure in North Dakota. Enhanced maturation resulted in Type II oil windows occurring at much shallower than expected depthS, SUMMARY at 2,300 m (7.544 ft). The Nesson anticline is believed to have had I. The Bakken Formation consists of three members. a lower and an important control on hydrocarbon potential. an upper shale and a middle member. The middle member Production from the Bakken Formation occur at long distances consists of multiple lithofacies which are correlative across the from the regions of significant hydrocarbon generation (vitrinite studyarea. reflectance = 0.7 percent) and expulsion threshold (vitrinite 2. The middle member, overall, is considered to be a reflectance = 0.9 percent) (Osadetz el al., in review). Osadetz el transgressive deposit. based on its onlapping relationship with al. (in review, p. 84) noted that the "region sufficiently mature to the lower member. The lowermost unit of the middle member expel hydrocarbons occurs in an area south of the Missouri River, is probably regressive. It does not onlap the lower shale and a region unfavourably disposed to migrate oils into northeastern therefore, probably represents the low stand of Bakken seas. Williston Basin. Enhanced maturities are associated with high heat flows in the region of the North American Central Plains 3. Smaller scale transgressive and regressive pulses are exhibited conductivity anomaly" (Fig. 25). This anomaly is a 2,000 km by the deposition of the upper portions of the middle member. (3,220 mi) long. 80 km (129 mil wide feature along which The sandstone units represent intertidal cieposits with coincidental electrical conduclivity and heat flow anomalies associated tidal channels. Storm deposits are also presen t. occur. The Nesson structure is associated with this fcature. In locally. Canada. Osadetz ('I 01. (in revi elV. p. 31) noted that " .... Family B oils occur exclusively in th e Bakken Formation leservoirs al 4. The deposition 01' the middle member is further cOn1rlicated Ron eolt. Daly and Ro eanville fields". Production from the by the dissolulion of the Devoni

It is poss ible thai until I (Manitoba) and its correlatives in 6. Significant oil shows scatte red throughout til ,,' study area Saskat chewan and North Da kola, as we ll as channel sands noted suggesl a strong po tential for successful future exploration. in the,e areas, provided Ihe necessary conduit for oil migration and may rerresenl the "low s t ~ lnd sy,lelll" pl"Oposed by Osadetz (!I 7. The producing sandstone unil mapped in Ihe siudy are;1 may (II . (in review) ([Oig. 25) These Llcies. where develol1Cci in have pl'ovidedthc migration pathway for Bakkell oils. SIX'IH INTERNATIONAL WILLISTON BASIN SYMPOSIUM 93

ACKNOWLEDGMENTS Fuller'. JG.e.M., 1956, Mi ss iss ippian rocks anei oilfields ill soutllca ste rn Saskatchewan, Reg ina, Saskatchewan. The authors thank Sidney B. Anderson and Richard D. Saskatchewan Department of Mineral Resources Report LeFever for their critical reviews of thi s manuscripl. Figures were 19,72 p. expertly drafted by Ken Dorsher. Permission to publish the Manitoba data has been granted by The Honourable Harold J. Fuzesy, L.M., 1960, Corre lation and subcrops of th e Neufeld, Minister, Manitoba Energy and Mines. Mississippian strata in southeastern and south-central Saskatchewan, Regina, Saskatchewan, Saskatchewan REFERENCES Department of Mineral Resources, Report 5 1, 63 p. Gerhard, L.e., S.B . Anderson, J.A. LeFever, and e.G. Carlson, Anderson, S.B. and J.B. Hunt, 1964, Devonian salt solution in 1982, Geological development, origin, and energy north central North Dakota , ill W. Leskela, J. Brindle, mineral re sources of the Williston Basin, North Dakota, and S.H. Harris, eds., Third International Williston American Association of Petroleum Geologists Bulletin, Basin Symposium, Billings Geological Society , North v. 66, p. 989-1020. Dakota Geological Society, and Saskatchewan Geological Society, p. 93-104. Gerhard, L.e., S.B. Anderson, and J.A. LeFever, 1987, Structural Anderson, S.B. and R.P. Swinehart, 1979, Potash salts in the history of the Nesson anticline, North Dakota, in M.W. Williston Basin, U.S.A., Economic Geology, v. 74, p. Longman , ed., Williston Basin; anatomy of a cratonic 358-376. oil province, Denver, Colorado, Rocky Mountain Association of Geologists, p. 337-354. Baillie, A.D., 1953, Devonian System of the Williston Basin area, Winnipeg, Manitoba, Manitoba Mines Branch Gillard, D.R. and S.P. Jordan, 1984, Rocanville Bakken sand pool Publication No. 52-5, 104 p. infill drilling study, Septembe r 1984 , filed with Saskatchewan Energy and Mines, October 1984 , 62 p. Bjorlie, P.F. and S.B . Anderson, 197 8, Stratigraphy and depositional setting of the Carrington shale facies Green, A.G., W. Weber, and Z. Hajna l, 1985, Evolution of (Mississippian) of the Williston Basin, in J.M. Parker, Proterozoic terrains beneath the Willi ston Basin. ed., 4th Annual Field Conference Guidebook, Billings, Geology, v. 13, p. 624-628. Montana, Billings Geological Society, p. 165-176. Harms, J.e., J.B. Southard, and R.G . Walker, 1982, Structures and Brindle, J.E., 1960, Mississippian megafaunas in southeastern se quences in clastic rocks, Society of Economic Saskatchewan, Regina, Saskatchewan, Saskatchewan Paleontologist and Mineralogi sts Short Course No.9. Mineral Resources Report 45, 107 p. Ha yes, M.D., 1984 , Conodonts of th e Bakken Formation Carlson , C.G. and J.A. LeFever, 1987 , The Madison, a (Devonian and Mississippian), Williston Basin, North nomenclatural review with a look to the future , in e.G. Dakota, Master's thesis , University of North Dakota. Carlson and J.E. Christopher, eds., Fifth International Grand Forks, North Dakota, 178 p. Williston Basin Symposium, Regina, Saskatchewan, Saskatchewan Geological Society Special Publication 9, Heck, T , 1979, Depositional environments and diagenesis of the p.77-82. BOllineau interval (Lodgepole) in North Dakota. Master'S thesis, University of North Dakota, Grand Christopher, J .E., 1961, Transitional Devonian-Mississippian Forks, North Dakota, 227 p. Formations of southern Saskatchewan, Regina, Saskatchewan, Saskatchewan Mineral Resources Report Hester, T.C. and J.W . Schmoker, 1985, Selected physical 66, 103 p. properties of the Bakken Fomlation, North Dakota and Montana part of th e Williston Basin, U.S. Geological Christopher, J.E., 1962, The Three Forks Group (U pper Survey, Oil and Gas Investigations Chart OC-126. Devonian-Kinderhookian) of southern Saskatchewan, in A.R. Hansen and J.H . McKeever, eds., Three Forks and Holland, F.D., M.D. Hayes, Le. Thrasher, and T.P. Huber, 1987. Belt Mountains area, The Devonian System of Montana Summary of the biostratigraphy of the Bakken and adjacent areas, 13th annual field conference and Formation (Devonian and Mississippian) in the symposium, Billings, Montana, Billings Geological Williston Basin , North Dakota, in e.G. Carlson and J.E. Society, p. 67-77. Christopher, Fifth Internat ional Williston Basi n Symposium, Regina, Saskatchewan, Saskatchewan Dow, W.G., 1974, Application of oil-correlation and source-rock Geological Society Special Publ ica tion No.9, p. 68-76. data to exploration in Williston Basin, American Association of Petroleum Geologists Bulletin , v. 58, Holter, M.E., 1969, The Middle Devonian Prairie Evaporite of p. 1253-1262. Saskatchewan, Regina, Sask atchewan, Saskatchewan Dumonceaux, G.M., 1984, Stratigraphy a nd depositional Department of Mineral Resources Report 123 , 133 p. environments of the Three Forks Formation (Upper Johnson , H.D. , 1978 , Shallow siliciclastic seas, in H.G. Reading. Devon ian ), Williston Ba sin, North Dakota, Master's ed ., Sedimentary Environments and Facies. Palo Al to . thL:sis, Universi ty of North Dakota, Grand Forks, North California, Blackwell Scientific Publications. p. 207· Dakota, 189 p. 258. Ed wards, Wand W.M. Last, 1991 , Petrology of middle Bakken Karma, R. and G.R. Pars low, 19 89. Sedimentology and member in the Daly fiel d, southwestern Man itoba, ill ge ochemistry of the Bakken Formation (Devoni an ­ The Sixth Intemational Williston Basin Symposium Mississippian) ill southern Saskatchewan, ill Summary Elliot. T ., 1978, Cl as ti c Shore lines, in H.G . Re ading, ed ., of In vestiga tion s 1989, Regina. Saskatchewan. Sedimentary Environme nt s and Facies. Palo Alto. Saskatchewan Geologi cal Survcy Mi sc. Report 89-4. California, Blackwell Scientific Publications, fl. 14 3-177. [l 14l -147. 94 SIXTH INTERNATI ONAL WILLISTO/\ BASIN SYMPOSIUM

Kent , D.M ., 1984 , Carbonate and associated roc ks of the Williston Pal eozoic petroleunl source rocks, their di stribution, Basin : th eir origin, diagenesis, and economic potent ial , ri chness and thermal matu rity in Canadian Williston Den ver, Colorado, Rocky Mountain Section - Society of Basin (sou th eastern Saskatchewan an d southwestern Economic Paleontologists and Min eralogists, 137 p. Manitoba) , Bulletin of th e Geological S urvey of Kume, 1. , 1963, The Bakken and Englewood format ions of North Canada. Dakota an d northwestern South Dakota, Grand Forks, Osadetz, K. G., L.R. Snowdon, an d P.W . Brooks, thi s volume, North Da ko ta, North Dakota Geological Survey Bulletin Relationships amongst oil qu ality, th ermal maturity and 39,87 p. po st- acc umulation alteration in Canadian Williston LeFever, 1.A., R.D. leFever, and S.B. Anderso n, 1987, Structural Basin , southeastern Saskatchewan and southwestern evolution of th e central and so uthern portions of the Manitoba, in The Sixth International Willi ston Ba sin Nesson anticline, North Dakota, in Carlson, e.G., and Symposium. 1.E. Christopher, eds., Fifth International Willi ston Price, L.e., T. Ging, T. Daws, A. Love, M. Paw lewicz, and D. Bas in Symposium, Regin a, Saskatchewan, Anders, 19 84, Organic met am orphism in the Saskat chewa n Geological Society Special Publication Mississippian-Devonian Bakken shale North Dakota No.9, p. 68-76. portion of the Willi sto n Basin , in 1. Woodward, F.F. Lineback, 1.A. and M.L Davidson, 1982, The Williston Bas in - Meissner, and 1.L Clayton, eds., Hyd rocarbon source sediment-starved during the Early Mississippian, ill 1.E. rocks of th e greater Rocky Mountain region, Denver, Christopher and 1. Kaldi, eds., Fourth International Colorado, Rocky Mountain Association of Geologists, Willi ston Basin Symposium, Regina, Saskatchewan, p.83-133. Saskatc hewan Geological Society Special Publ icatio n 6, Sandberg , e.A., [964, Precambrian to Miss issippian paleotectonic p.125-130. of th e southern Willi ston Basin, an abstract, in W. Macaul ey, G., D.G . Pen ner, R.M. Procter, and W.H. Tisda ll , Leskela, 1. Brindle, an d S. H. Harris, eds., Third 196 [, Carboniferous, in R.G. McCrossan, ed., Geo[ogic International Willi ston Basin Symposium, Billings hi story of western Canada, Calgary, Alberta, Alberta Geo [ogical Society, North Dakota Geo[ogical Society, Society of Petroleum Geo[ogists, p. 89-102. and Saskatchewan Geo[ogical Socie ty, p. 37-38. Mac Donald, G.H., 1956, Subsurface stratigraphy o f the Sandberg, e.A., R.e. Gutshick. J.G. Johnson, F.G. Poo le, and Mississippian rocks of Saskatchewan, Ottawa, Ontario , W.J. 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Hes ter, [983, Organic carbon in th e McCabe, H.R., J963, Mi ssissippi an oil fields of southwestern Bakken Forma tion, United States portion of Wi[liston Manitoba, Winnipeg, Manitoba, Manitoba Mines Basin, Ame rican Association of Petroleum Geo[ogists Branch Publication 60-5 , 50 p. Bu[letin, v. 67, p. 2 [65-2174. McCabe, H.R ., [966, T ec toni c fram ework of Pal eozoic Thomas, G.E., 1954, The Mi ss iss ippian of the northeastern formations in Manitoba, Annual Western Meeting, Williston Basin, Canadian Mining an d Metal[urgical CIM, Calgary, Transactions, v. LXX, p. 180- 189. Transaction s, v. LVII , p. 68 -74. McCabe, H.R., 1980, Structure contour and isopach map - Thrasher, L.e., 1985, Macrofossils and bi os tratigraphy of th e Devonian - Prairie Ev aporite Formation, Winnipeg, Bakken Formation (Devonian and Mississippian) in Manito ba, Manitoba Ene rg y a nd Mines Mine ral western North Dak ota, Master's th esis, University of Resources Di vision Stratigraphic Map Series Dpe - 1. North Dakota, Grand Forks, North Dakota , 292 p. Me issner, F.F., 1978, Petroleu m geology of the Bakken Walker, R. G., 1979, Turbidites and ass ociated coarse clasti c Formation, Williston Basi n, North Dakota and Montana, deposits, in R.G . Walker. ed. , Facies Mode ls, ill D. Estelle and R. Miller, eds., The Economic Geoscience Canada Reprint Seri es [, p. 91-104. Geo logy of th e Williston Basin, 1978 Williston Bas in Webste r, R.W., [982, Analysis of petroleum so urce ro cks of the Sympos ium , Billings, Montan a, Montana Geological Bakken Formation (Devonian and Mi ss iss ippian) in Soc iety, p. 207-230. North Dakota, Master's the sis, University of North Nordquist , 1.W ., 1953, Mi ss issi ppian stratigraphy of northern Dakota, Grand Forks, North Dakota, 150 p. Montana, in 1.M. Parke r, ed ., 4 th Annual Field Webster, R. W., 1984, Petroleum source rocks and strati graph y of Conference Guidebook, Bdlings, Mont ana, Billings the Bakken Form ation in North Dakota, ;1'1 1. Geological Society, p. 68-82. Woodward, F.F. Meissner. and J.L. Cl ay ton, eds .. Osadetz, K.G., P.W. Brooks, and L.R . Snowdon, in review, Oil Hydrocarbon source rocks o f th e grea ter Rocky familie s, their sources and mi gration pathways in Mountain region, Denver, Colorado. Rocky Mountain Canadian Williston Ba si n (southeastern Saskatchewan Association of Gcologists. p. 57 -82 . and southwestern Mani to ba). Bulletin of th e Ge ologica l Williams, J.A., [974, Characterization of oil Iy pes in Will is ton Survey of Canada. ~ Bas in, Am erican Associati on of Petrolcum Geo[ogists Osadetz, KG . and L.R. Snowdon. ill rev ie w, S igni fica nt Bullel in, v. 58 , no. 7. p. 1243 · 1252.