Petroleum Potential of the Middle Member, Bakken Formation, Williston Basin
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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 /"- '- .'IF-r- , . ...... / A I '·~·#-0'+. I I lBERTA i ..o;;.~~~~ \ ~1 I SAS"Arc~w;".......... ~ \ 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<or k> 9"o,-IHO)Wn, BAKKEN _, ';"'-9'O;l'<Id, 001(.0,.0 .... ,."., b4dd0O"I~",;,.o, __ llaf~- 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, .. <y'"h-Drow1I.b<cr-nond9<Ol , 12, T.157N., R.95W. in Williams County, North Dakota. As ""1 I, ... IJ c'J1101!,r.~ based on samples, the formation is 32 m (105 ft) thick at its type section and consists of two black, organic-rich shales which are separated by a light grey to grey-brown, very fine-grained, Figure 3: Type log for the Bakken Form ation from Amerada Petroleum Corporation - H.O.