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Chapter 2 Province—Stratigraphic and Structural Framework to a Geologic Assessment of Undiscovered Oil and

Gas Resources Click here to return to Volume Title Page

By Lawrence O. Anna, Richard Pollastro, Stephanie B. Gaswirth

Chapter 2 of 7 Assessment of Undiscovered Oil and Gas Resources of the Williston Basin Province of , , and , 2010

By U.S. Geological Survey Williston Basin Province Assessment Team

U.S. Geological Survey Digital Data Series DDS–69–W

U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation: Anna, L.O., Pollastro, Richard, and Gaswirth, S.B., 2013, Williston Basin Province—Stratigraphic and structural framework to a geologic assessment of undiscovered oil and gas resources, chap. 2 of U.S. Geological Survey Williston Basin Province Assessment Team, Assessment of undiscovered oil and gas resources of the Williston Basin Province of North Dakota, Montana, and South Dakota, 2010 (ver. 1.1, November 2013): U.S. Geological Survey Digital Data Series 69–W, 17 p. iii

Contents Abstract...... 1 Introduction ...... 1 Province Boundary...... 1 Physiography...... 2 Stratigraphic Setting...... 2 Major Sequences...... 3 Sauk...... 3 Tippecanoe...... 5 Kaskaskia...... 5 Absaroka ...... 7 Zuni...... 8 Tejas...... 8 Tectonics and Structural Setting...... 8 ...... 8 Wrench Fault System...... 10 Structure-Stratigraphic Model ...... 11 Carbonate System...... 12 Basin Production...... 12 Assessment Results...... 14 Acknowledgments...... 16 References Cited...... 16

Figures 1. Map showing location and physiographic features of the Williston Basin Province...... 2 2. Map showing thickness of Phanerozoic strata in the Williston Basin...... 3 3. Schematic diagram showing bounded slices of Phanerozoic strata in the Williston Basin...... 4 4. Diagram showing geologic time scale, major stratigraphic sequences, first- and second-order sea level curves, and ages of source and reservoir rocks in the Williston Basin...... 5 5. Generalized stratigraphic chart and associated total petroleum system for the Williston Basin...... 6 6. Maps showing Williston Basin depositional patterns of the Tippecanoe and lower Kaskaskia sequences...... 7 7. Maps showing Precambrian structural and tectonic configuration of the Williston Basin and surrounding area...... 9 8. Structural configuration of the Williston Basin contoured on subsea elevations on top of the ...... 11 9. Diagram showing possible relation between lineaments mapped at the surface and fault configuration at depth...... 12 10. Diagram showing oil and gas production in the Williston Basin...... 13 11. Map showing oil and gas production distribution in the Williston Basin Province...... 14

Table 1. Williston Basin Province assessment results...... 15

Williston Basin Province—Stratigraphic and Structural Framework to a Geologic Assessment of Undiscovered Oil and Gas Resources

By Lawrence O. Anna, Richard Pollastro, Stephanie B. Gaswirth

Abstract Montana (fig. 1). The assessment was based on geologic prin- ciples and applied the total petroleum system (TPS) concept. The U.S. Geological Survey completed an assessment of A TPS consists of one or more assessment units (AUs), which the undiscovered oil and gas potential of the Williston Basin are mappable parts of a petroleum system in which discovered in 2008. The assessment of undiscovered oil and gas used and undiscovered fields constitute a single, relatively homoge- the total petroleum system concept, which includes mapping neous population. The assessment methodology was based on the distribution of potential source rocks and known petro- the numerical simulation of the estimated number and sizes of leum accumulations and determining the timing of petroleum undiscovered fields. The TPS includes all genetically related generation and migration. This report is an introduction to the petroleum within a limited, mappable geologic space, along geologic features that were used to develop conceptual models with other essential mappable geologic elements (reservoir, used in the assessment process. The assessment focused on seal, and overburden rocks) that control the fundamental the geologic framework of the basin to determine the origin of processes of generation, expulsion, migration, entrapment, source and reservoir rocks, timing and type of tectonic events and preservation of petroleum (Magoon and Dow, 1994). and the configuration of resulting structures, formation of traps Assessment units are assessed individually depending on their and seals, and thermal history of the basin. homogeneity in terms of geology, exploration considerations, Six major stratigraphic sequences, each bounded by and geologic risk. major can be distinguished within the more This chapter describes the geologic framework for the than 16,000 ft of Phanerozoic rocks in the Williston Basin. Williston Basin and some of the conceptual models and guid- The influence of paleostructure on is reflected by lithofacies distribution and thickness patterns resulting ing principles used in the assessment of oil and gas resources. from the presence of numerous types of structures. Recurrent movement of blocks occurred periodically, resulting Province Boundary in a variety of depositional environments and the development of drape folds involving the overlying sediments. These faults The province boundary used in the 1995 USGS petro- and resulting features are manifested either as linear features leum assessment of the Williston Basin (Peterson and on a paleosurface of deposition or on the present-day surface Schmoker, 1995), as used in this assessment, was drawn on as lineaments. county and State borders that were completely or partially Production history plots indicate that the Williston Basin within the geologically defined Williston Basin. The eastern has gone through several production cycles in both oil and gas; boundary (North Dakota State boundary) and the southern current (2008) cumulative production is 2,740 million barrels boundary (central South Dakota) are geologically defined as of oil (MMBO) and 2,700 billion cubic feet of gas (BCFG) with most of the production from the Madison the eastern and southern subcrops of Paleozoic and Group and Red River Formation reservoirs. Cur- formations. The western boundary in Montana and Wyoming rent monthly production is 7.7 MMBO and 11.9 BCFG. is drawn near the eastern edge of several Laramide structural uplifts that geologically define the Williston Basin. Some fields, however, in corners of the western province boundary Introduction are part of the Powder River Basin and were not included in the Williston Basin Province. Therefore, a surrogate western The U.S. Geological Survey (USGS) completed a quanti- boundary was drawn that clips the westernmost corners of the tative estimate of the undiscovered oil and gas potential of the province boundary to exclude those fields that are not part of Williston Basin Province of North Dakota, South Dakota, and the Williston Basin Province (fig. 1). 2 Williston Basin Province—Stratigraphic and Structural Framework of Undiscovered Oil and Gas Resources

108° 107° 106° 105° 104° 103° 102° 101° 100° 99° 98° 97°

BOWDOIN POPLAR GOOSE LAKE DOME FAULT ZONE FAULT ZONE 49° CANADA USA

NESSON POPLAR Williston 48° DOME Minot Grand Forks

Sidney BILLINGS ANTICLINE MONTANA BROCKTON-FROID FAULTCEDAR ZONE CREEK LITTLE KNIFE 47° Glendive ANTICLINE Mondak trend Jamestown ANTICLINE Fargo Dickinson Bismarck

Miles Sheep Mountain MILES CITY City ARCH syncline 46° NORTH DAKOTA

SOUTH DAKOTA West Assessment Boundary 45° Sheridan WYOMING TRANSCONTINENTAL ARCH CANADA BLACK Pierre Gillette Williston Basin MT ND HILLS 44° Rapid City Province SD WY

0 25 50 MILES

0 25 50 KILOMETERS Figure 1. Location and physiographic features of the Williston Basin Province. Black lines not labeled are major lineaments or faults. Solid red line is province boundary; dashed red line represents the western boundary for assessment units. Lineaments and structure locations are from Gerhard and others (1982) and Anna (1986). Physiography Stratigraphic Setting

Several structural features border the Williston Basin Prior to the Phanerozoic Eon, the middle part of the (fig.1). To the west and southwest are Laramide or rejuvenated United States consisted of a thin North American craton on Laramide structures including the Black Hills uplift, Miles which relatively thin discontinuous Paleozoic sediments City arch, Bowdoin dome, and Porcupine dome. Major struc- were deposited on the Cordilleran shelf. Continent margins, tural features include the Bow Island arch to the northwest and the Canadian Shield to the northeast in Canada (neither are however, including the western Cordilleran, Appalachian, shown on fig. 1) and the Transcontinental arch to the south- and Gulf Coast, consisted of thick, mostly continuous geo- east (fig. 1). Physiographic or ecosystem classification for the synclinal marine sediments. The Williston Basin is part of the basin includes the provinces of the Great Plains, Northwestern North American craton where the sedimentation history can be Glaciated Plains, Northern Glaciated Plains, Northeastern described as carbonate deposition in the Paleozoic and clastic Glaciated Plains, Red River Valley, Western Glaciated Plains, deposition in the Mesozoic and Cenozoic, and where thickness North-Central Great Plains, Black Hills, and the Powder River of Phanerozoic strata is more than 16,000 ft in the basin Basin (Bailey and others, 1994). center (fig. 2). Stratigraphic Setting 3

Paleozoic carbonate rocks (except for the initial Pha- third-order and fourth-order cycles may be the result of tectonic nerozoic transgression that deposited and Lower activity or a combination of tectonics and eustacy. Because Ordovician clastic sediments) are stacked, cyclic, and vary in water depths in the basin during the Phanerozoic were relatively thickness. All are punctuated by minor to extensive hiatuses shallow, a small change in water depth resulted in substantial (Sloss, 1984; Meissner and others, 1984; Gerhard and others, depositional environment and sedimentation changes. 1982) resulting in numerous unconformities (fig. 3) that gave rise to primary and secondary dissolution, deposition of numerous salt and anhydrite beds, and secondary dolomitiza- Sauk tion of . Mesozoic and Cenozoic deposition was mostly of clastic The Sauk major sequence consists of the Upper Cambrian sediments in a variety of environments, including continental, (figs. 4 and 5), which represents the ini- shoreline, and basin settings. Lithologies include mudstone, tial stages of a major first-order transgression over a low-relief , , siltstone, and coal. Precambrian surface, although some major structural features exerted some control over thickness patterns, such as the Nesson anticline (fig. 1). At the end of Sauk time, the Williston Major Sequences Basin started to subside as a result of strike-slip movement on major northeast–southwest trending faults (Gerhard and There are six major depositional sequences, each bounded by major unconformities (Sloss, 1984), which can be distin- Anderson, 1988). At that time, subtle structural features, such guished within the Phanerozoic rocks of North America (fig. 4). as block and linear horsts and grabens, began influencing sedi- They are from oldest to youngest, the Sauk, Tippecanoe, mentation patterns on a broad scale. The sediment source for Kaskaskia, Absaroka, Zuni, and Tejas. Major sequences that con- the Deadwood was from weathered Precambrian rocks, eroded sist of first-order and second-order cycles in the Williston Basin from highlands to the east or from the Transcontinental arch to are probably the result of eustatic changes in sea level, although the southeast (fig. 1) (Carlson and Thompson, 1987).

100˚ 105˚ 49˚

10 8 N O R T H D A K O T A 9 10 16

15 M O N T A N A 14 13 12 11 10 10 9 8 8 1

10 7 6 45˚ 5 4 3 2

W Y O M I N G S O U T H D A K O T A

10 2 3 4 0 50 100 KILOMETERS

0 50 100 MILES

Figure 2. Thickness of Phanerozoic strata in the Williston Basin; maximum thickness is more than 16,000 ft in west-central North Dakota. Contour interval is 1,000 ft. 4 Williston Basin Province—Stratigraphic and Structural Framework of Undiscovered Oil and Gas Resources

Tertiary

Cretaceous

Jurassic

Triassic

Mississippian

Devonian

Silurian

Ordovician

Cambrian Precambrian

Figure 3. Schematic diagram showing unconformity bounded slices of Phanerozoic strata in the Williston Basin. Individual slices demonstrate the relative extent of the basin and the effects of basin margin erosion at the times indicated. The vertical axis shows relative thickness of the rocks that were deposited. Note that the distribution of the Cambrian, , , and Tertiary slices indicates an open-ended basin (to the left) as opposed to a closed basin. Modified from Kent and Christopher (2008). Stratigraphic Setting 5 600 550 500 450 400 350 300 250 200 150 100 50 0 GEOLOGIC Mississippian Neogene Cretaceous Devonian Triassic

Ordovician TIME Cambrian Jurassic Precambrian SCALE, (part) Ma Plio E E L PETROLEUM Pal Eoc Olig Mlio M M M M M E L E E E E E E E L M L L L L L L L SYSTEM EVENTS

SOURCE ROCK

RESERVOIR ROCK

Salk Tippecanoe Kaskaskia Absaroka Zuni Tejas SEQUENCE

Rise 1st order cycles SEA LEVEL CHANGE

2nd order cycles Fall

Figure 4. Diagram showing geologic time scale, major stratigraphic sequences of Sloss (1984), first- and second-order sea level curves from Vail and others (1977), and ages of petroleum source and reservoir rocks in the Williston Basin. Solid black intervals in source rock column are for thick accumulations; thin lines indicate association with carbonate depositional cycles. In reservoir rock column, green is for oil and red for gas; thin lines indicate generalized reservoir rock and do not necessarily represent the full spectrum of possible reservoirs. E, Early; M, Middle; L, Late; Pal, ; Eoc, Eocene; Olig, Oligocene; Mio, Miocene; Plio, Pliocene.

There are several minor transgressions and regressions The Red River Formation conformably overlies the Winnipeg within the Deadwood Formation that divide the formation and is the initial unit that was deposited during numerous into several members (LeFever, 1996). A major unconformity cycles of shallow marine carbonate and anhydrite and salt developed at the end of Deadwood time resulting in the trun- sedimentation. Each cycle consists of a basal shelf limestone cation of most of the upper members as well as parts of the overlain by laminated dolomite and capped by anhydrite. lower members around the basin margin. The unconformity Conformably overlying the Red River are the Stony Mountain also marks the end of Sauk deposition. and Stonewall Formations and the Interlake Group. Third- Depositional environments of the Deadwood include and fourth-order cycles in these strata continue the pattern shallow marine, coastal plain, and rare alluvial plain, with of cyclic sedimentation, consisting of subtidal limestone, successions of sandy carbonate, mudstone, siltstone, and intertidal dolomite and dolomitic limestone, and peritidal or quartz arenites (burrowed and nonburrowed). The formation is supratidal anhydrite or salt. For example, there was a brief recognized for its abundant glauconite that gives it a familiar regression after the deposition of Ordovician Stony Mountain greenish color. and Stonewall Formations followed by a brief transgression at the beginning of the Silurian resulting in the deposition of the Interlake Group, which is also punctuated by several Tippecanoe cycles. Tippecanoe sedimentation was terminated by a major The Tippecanoe major sequence marks the start of the regression near the end of the Silurian, and subsequent erosion second transgression-regression cycle, and also marks the removed parts of the Interlake Group, as well as the Stony beginning of Ordovician sedimentation (fig. 4). Depositional Mountain, Stonewall, and Red River Formations, especially patterns indicate that as the basin started to form, there was around the basin margin. a seaway connection to the Cordilleran sea to the southwest (Gerhard and others, 1990). During the initial transgression, Kaskaskia the Winnipeg Group was deposited as a succession of shallow marine sandstone, shale, and shaly carbonate. The Winnipeg The Kaskaskia major sequence part of the first-order unconformably overlies the Deadwood except in the eastern regressive cycle began in the Ordovician (Tippecanoe part of the basin where it rests on Precambrian basement. sequence) and continued into the Jurassic until it was 6 Williston Basin Province—Stratigraphic and Structural Framework of Undiscovered Oil and Gas Resources

Period Units Total Petroleum Systems

Tertiary Fort Union Coalbed Gas

Cretaceous Pierre Shallow Biogenic Gas Jurassic Nesson Triassic Spearfish Permian Minnekahta Opeche Minnelusa Pennsylvanian Amsden Tyler Tyler Otter Kibbey McCone Co. , Montana

Charles Poplar, Montana Mississippian Canada Canada Madison Mission Canyon

Lodgepole

Bakken Bakken-Lodgepole Three Forks

Birdbear

Duperow Duperow Devonian Souris River

Dawson Bay Prairie

Winnipegosis Winnipegosis Cedar Creek Paleozoic Composite Ashern Silurian Interlake

Stonewall Red River Stony Mountain Ordovician Red River

Winnipeg Winnipeg-Deadwood Cambrian Deadwood

Figure 5. Generalized stratigraphic chart and associated total petroleum system (TPS) for the Williston Basin. Length of the TPS box corresponds to the assessment units associated with the TPS; colored circles indicate oil in an assessment unit (AU) in which there is some uncertainty as to its origin. Colored boxes in the unit column indicate formations that are thought to contain source rocks for the TPS. Modified after Paul Lillis (USGS, written commun., June 2, 2008). terminated by an extended series of transgressive events that In the Elk Point Basin, the numerous cycles of restricted began with the Zuni major sequence fig. 4). The Kaskaskia marine conditions were followed by episodes of normal begins with a second-order transgressive event in the Early circulation coupled with sea level change, giving rise to a Devonian and concludes as a major regression at the end of variety of lithologic successions of limestone, dolomite and the Mississippian. In addition, uplift of the Transcontinen- evaporite. For example, there are three second-order cycles in tal arch (which is part of the Colorado lineament of Warner, the Kaskaskia (fig. 4).The first is an initial transgression that 1978) created a major change in basin configuration from a deposited the Ashern and Winnipegosis Formations followed largely circular basin in northwestern North Dakota with a by the Prairie Formation, which represents a regression result- southwestern marine connection to the Cordilleran sea, to a ing from a major restriction at the margin of the Elk Point northwest–southeast trending elongated shelf basin. This basin Basin. The second transgression reestablished normal marine extended from northwestern North Dakota to the northern part circulation in the basin that resulted in the deposition of the of Alberta, Canada, with a marine connection to the Arctic Dawson Bay Formation. As sea level regressed, the Souris Ocean. The Williston Basin became the southeastern corner of River, Duperow, Birdbear, and Three Forks Formations were the newly formed Devonian Elk Point Basin (fig. 6). deposited. The third major transgression occurred during Stratigraphic Setting 7

ELK POINT BASIN

N N

0 200 KILOMETERS 0 200 KILOMETERS Transcontinental arch 0 200 MILES Transcontinental arch 0 200 MILES A. TIPPECANOE SEQUENCE B. LOWER

ROCK TYPES Dolomite Limestone Shale

Figure 6. Maps showing Williston Basin depositional patterns of the Tippecanoe and lower Kaskaskia sequences. A, Ordovician to Late Devonian, showing southwest and southeast seaway connections. B, Late Devonian to Early Mississippian, showing a northwest seaway connection through the Elk Point Basin in Canada. In Middle Mississippian the basin switched to its original (Ordovician to Late Devonian) configuration. Arrows indicate direction of water movement. Modified from Gerhard and Anderson (1988). the Late Devonian resulting in the deposition of the Bak- Kaskaskia strata exhibit a range of depositional environ- ken Formation. The organic-rich marine shale of the Bakken ments, including subtidal, intertidal, and rare supratidal with represents the first major input of clastic material into the various percentages of dolomite, limestone, salt, and anhy- Williston Basin since the Cambrian Deadwood and Winnipeg drite. Pinnacle reefs are common in the deeper subtidal envi- Formations. As sea level receded and there was reduced clastic ronments of the Winnipegosis Formation in Canada, whereas input into the basin, the Mississippian Lodgepole Limestone patch reefs are most common in shallower parts of the shelf in was deposited in subtidal conditions resulting in low porosity western North Dakota and eastern Montana. . During middle Lodgepole time (Early Mississippian), Absaroka there was a shift from the northwest–southeast elongated Elk Point Basin back to a circular basin configuration, with the The Absaroka major sequence represents the upper part depocenter reestablished in northwestern North Dakota (fig. 6) of a first order regression, and includes several secondary (Gerhard and others, 1990). Structural adjustment in central transgressive and regressive cycles in a relatively low sea Montana created a narrow marine connection (the Montana level environment (fig. 4). The initial second-order trans- trough) to the Cordilleran sea. Following deposition of the gression was from the southwest, concurrent with uplift of Lodgepole, there was a renewed cycle of alternating depo- areas to the east, west, and south that became major sources sitional transgressions and regressions during deposition of of clastic sediment shed into the Williston Basin. The rock sequence includes interbedded sandstone, siltstone, shale, the upper part of the , resulting in a pattern and limestone of the Pennsylvanian Tyler Formation and of open marine and intertidal limestones and peritidal and equivalents; the overlying Minnelusa Formation records anhydrite and salt deposits. A major regression marks input from the Ancestral Rocky Mountain orogenic belt and the top of the Mississippian , which over- the Transcontinental arch. The sediments were deposited in lies the Madison and is the uppermost unit of the Kaskaskia alluvial plains, as well as in nearshore and shelf environments sequence (fig. 4). This regression marked the end of the last from prograding delta systems and in barrier island environ- major Paleozoic marine sedimentation in the Williston Basin ments (Sturm, 1982; Land, 1979). With continued regression, (Gerhard and others, 1982). sedimentary processes appear to have been influenced in 8 Williston Basin Province—Stratigraphic and Structural Framework of Undiscovered Oil and Gas Resources part by restrictive conditions, as indicated by the deposition Quaternary and consisting of continental gravel, sandstone, of thin platform carbonates and light-colored clastics, pro- siltstone, mudstone, and low-grade coal. There are reported grading sands over shallow marine sediments, and thick minor shallow biogenic gas accumulations in the northern, accumulations of salt in the center of the basin, as well as by eastern, and southeastern parts of the basin, although the subaerial exposure of units during the Permian (Gerhard and resource has not been thoroughly evaluated. There is also others, 1982). potential for coalbed methane (CBM) accumulations in the Major unconformities occur near the end of the western part of the basin, but the full potential of this resource Pennsylvanian, end of the Permian, and end of the Triassic has likewise not been evaluated. (Gerhard and others, 1990). The latter had the most profound effect by eroding significant parts of pre-Triassic strata, espe- cially near the north and east margins of the Williston Basin; the truncation created stratigraphic traps that account for most Tectonics and Structural Setting of the production in Canada. Precambrian

Zuni The geologic history of the Precambrian basement of the Williston Basin is critical to an understanding of the basin’s The Zuni major sequence represents Jurassic and evolution, structural configuration, sedimentation, and thermal Cretaceous strata that were deposited as a first-order cycle patterns. There are two important components to basin devel- (fig. 4). The major sequence also represents a lithogenetic pack- opment—the Trans-Hudson orogenic belt (Green and others, age bounded by regional unconformities. The package of rocks 1985b) and the northeast–southwest trending Proterozoic lin- is similar to the upper part of the Absaroka sequence, with eament and structural zones (Burrett and Berry, 2000; fig. 7A). successions of light-colored sandstone and siltstone and minor carbonate and salt. Three major chronostratigraphic units are The Trans-Hudson belt sutured the Archean Superior craton to separated by unconformities: (1) Middle and Upper Jurassic, the Archean Wyoming craton (fig. B7 ); the resulting collision (2) Lower Cretaceous, and (3) Upper Cretaceous and Tertiary created a north–south trending strike-slip fault and shear belt. through Paleocene (fig. 3) (Shurr and others, 1989). A basin center was created, caused in part by later folding of In the Lower Jurassic, there is a well-defined depocenter, the Trans-Hudson orogenic belt and rifting (Green and others, with anhydrite and salt at the basin center, shale and calcareous 1985a), although Nelson and others (1993) stated that there is shale toward the basin margins, and carbonate and sandstone a lack of direct evidence of a rift. at the basin margins. At the end of the Jurassic, there was a Burrett and Berry (2000) described the Trans-Hudson transition from marine subtidal and intertidal environments to orogeny (post 1,600 Ma) to include northeast-trending fault continental sandstone and mudstone. and lineament zones (fig. A7 ). These fault zones were later In the Lower Cretaceous there was a major first-order renamed as the Transcontinental arch (Colorado lineament transgression punctuated with two second-order regressions of Warner, 1978) (fig. 1), Brockton-Froid fault zone, Great and transgressions. There was no defined basin configuration, Falls tectonic zone, Poplar fault, and Hinsdale fault. In the only a gradual thinning from west to east. Lithologies are Neoproterozoic, these Precambrian structures were reacti- mostly sandstone, siltstone, mudstone, and shale. In the Upper vated, creating new north–south and northwest–southeast ori- Cretaceous, there were four major transgressions and regres- ented structures that were precursors to structures or zones of sions with a vague depocenter that developed in the south- weakness that formed the Nesson, Cedar Creek, Little Knife, western part of the Williston Basin. The end of the Zuni was and Billings (fig. 1), the Bismarck-Williston linea- marked by the fourth regression (top of the Cretaceous Hell ment, and Goose Lake trend, as well as a mosaic of small- Creek Formation; see fig. 5) that coincides with the lower part scale structures that are pervasive throughout the Williston of the Paleocene (fig. 4). Basin. Rocks in the Zuni major sequence have not produced nor Geophysical methods to map these structures include generated thermogenic hydrocarbons; only biogenic gas has gravity and magnetic surveys, which define large-scale been generated and produced in Upper Cretaceous Precambrian fault blocks, including their orientation and and siltstones. Minor amounts of biogenic and possibly migrated length. These geophysical methods are important attributes thermogenic gas have been produced in Cretaceous and Tertiary to help interpret structural and sedimentation trends. Seismic strata in the eastern and southeastern parts of the basin. interpretation, especially 3-D seismic, can refine gravity and magnetic interpretations. Five seismic lines were interpreted Tejas as part of this assessment (see chapter 6, this CD-ROM). Numerous faults, most of which are thought to be rooted in The Tejas major sequence represents the final first-order Precambrian rocks, were mapped but classed as approximate regression in the sedimentary history of the Williston Basin. or inferred because net offsets are small and difficult to map at It comprises three regional transgression-regression cycles the scale of the seismic profiles. A minor number of faults may (fig. 4) with strata ranging in age from mid-Paleocene through be attributed to salt dissolution. Tectonics and Structural Setting 9

115°W 105°W 95°W 2-1.9

60°N

8

50°N c

Williston Basin Province

c 40°N

l

s

– 0 500 MILES A–Arkara Gneiss GFTZ–Great Falls tectonic zone 0 500 KILOMETERS GSL–Great Slave Lake shear zone ICB–Idaho cobalt line EXPLANATION KFZ–Koonenberry fault zone LCL–Lewis and Clark line < 0.8 – 1.7 Ga PNG–Papua New Guinea P–Hauser Lake Gneiss 1577±3 Ma, 1.7 – 2.0 Ga Priest River Group > 2.7 Ga SAMZ–Striding Athabasca mylonite zone A. STZ–South Tasmanian zone

Figure 7. Precambrian structural and tectonic configuration of the Williston Basin and surrounding area. A, Tectonic map of the Northern Great Plains region (Burrett and Berry, 2000) showing northeast– southwest trending strike-slip faults; Williston Basin Province outline is shown for scale. Ga, billion years ago. B, Map showing configuration of the Trans-Hudson orogenic belt and associated north–south trending structures of the Williston Basin (modified from Nelson and others, 1993). 10 Williston Basin Province—Stratigraphic and Structural Framework of Undiscovered Oil and Gas Resources

50° Trans-Hudson orogenic belt CANADA

USA NORTH DAKOTA

48°

Superior craton Wyoming

craton 46° SOUTH ? DAKOTA MONTANA ? WYOMING Suture/rift 44°

106° 102° 98° 0 100 MILES PROVINCE BOUNDARY

0 100 KILOMETERS EXPLANATION Proterozoic island arcs or Archean cratons Major faults “Cordilleran-type” arc massifs

Archean-Proterozoic Highly reworked oceanic material boundary zones —former open oceans, fore-arc B. basins or back-arc basins

Figure 7. Precambrian structural and tectonic configuration of the Williston Basin and surrounding area. A, Tectonic map of the Northern Great Plains region (Burrett and Berry, 2000) showing northeast–southwest trending strike-slip faults; Williston Basin Province outline is shown for scale. Ga, billion years ago. B, Map showing configuration of the Trans-Hudson orogenic belt and associated north–south trending structures of the Williston Basin (modified from Nelson and others, 1993).—Continued

Paleozoic Wrench Fault System north–south thermal patterns are evident from present-day subsurface temperature measurements (see chapter 3, this Numerous studies have shown that surface lineament CD-ROM). patterns in the Northern Great Plains region, including the Cloos (1948) stated that the major tectonic features of Williston Basin, are a result of the reactivation of Precambrian several continents (based on his observations in Europe) have faults during the Phanerozoic (Thomas, 1974; Anna, 1986; been active during practically all of the tectogenetic periods of Earth’s history. Thomas (1976) postulated that the northeast– Brown and Brown, 1987; Maughan and Perry, 1986; Kent southwest and northwest–southeast orthogonal linear trends and Christopher, 2008; and Anderson, 2009). These studies for the North American continent developed during early show pervasive northeast–southwest and northwest–southeast Precambrian time, and the east–west, north–northwest, and trends that parallel major lineaments of Proterozoic terrane of north–northeast trends of secondary features developed during Burrett and Berry (2000) who described the Precambrian oro- later Archean and Proterozoic time. Based on these observa- genic history of north-central United States and south-central tions, it is believed that Precambrian tectonic events and their Canada. North–south trending lineaments that parallel the recurrent movement along preexisting zones of weakness Trans-Hudson structural system are less prominent, although played a major role in the development of most of the major Tectonics and Structural Setting 11

106° 104° 102° 100° 98°

49° –

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–

– –

– 47°

– –

– – –

– –

45° – –

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– 0 50 MILES

0 50 KILOMETERS

Figure 8. Structural configuration of the Williston Basin contoured on subsea elevations on top of the Red River Formation; contour interval 1,000 ft. Black line, boundary of Williston Basin Province. fault and shear systems in the Williston Basin. Although the drape folds of overlying sedimentary rocks. These faults and basin is generally reported as a sag or depression (fig. 8) and resulting features are manifested either as linear features on tectonically benign, its configuration is thought to be mostly a paleosurface of deposition or on the present-day surface formed as a result of structural deformation and down-to-the- (fig. 9). Wrench or strike-slip faults exist as simple shears basin block faulting from Precambrian rooted structures, as and are commonly associated with folds and with thrust and well as from deformation related to the Trans-Hudson oro- reverse faults. Scissor-type faults are also common and are genic belt. characterized by reversal of apparent dip-slip displacement along strike. Folds, thrusts, and reverse faults are commonly recognized as Laramide features, but are not generally directly Structure-Stratigraphic Model observed as pre-Laramide features. The change of topographic relief from one fault block to another is probably in the form The influence of paleostructure on sedimentation in the of a drape fold, not necessarily in the form of a fault plane. Williston Basin is reflected by lithofacies distribution and Basement faults have less effect on sedimentation distribution thickness patterns resulting from the presence of grabens, as the rock section thickens. However, the degree of drape is half-grabens, and horsts. Recurrent movement of basement primarily controlled by how far faults propagate upward. The blocks occurred periodically, with blocks being elevated at observed distribution and thickness of sediments in a deposi- one time and depressed another. Response of the rock col- tional system stem from recurrent movement of Precambrian umn to stress is regionally repetitive and is expressed by blocks as horsts, grabens, or half-grabens from eustatic structural patterns of faults, fractures, and folds that are also changes in sea level, and from the quantity and quality of repetitive. Reactivated Precambrian faults commonly created available sediments. 12 Williston Basin Province—Stratigraphic and Structural Framework of Undiscovered Oil and Gas Resources

Block Lineament Block Earth’s Lineament features surface

Mesozoic units

Paleozoic units

Precambrian basement

Figure 9. Diagram showing possible relation between lineaments mapped at the surface and fault configuration at depth. Several lineaments or groups of lineaments may represent one or two faults at depth, but one lineament does not necessarily represent one fault. Modified after Shurr (1982).

Carbonate System develop predominantly in transgressive systems tracts when a depressed platform is drowned. Physically, these two source Paleozoic carbonate units in the Williston Basin exhibit rock types can look similar because both are products of high several orders of depositional cycles, from first-order repre- carbonate productivity systems. Carbonate margin source senting hundreds of feet of rocks to fourth- and fifth-order rocks develop in transgressive systems tracts on low carbonate cycles that represent only a few feet. The carbonate systems productivity margins during periods of upwelling and or ocean exhibit numerous third- and fourth-order cycles of small-scale anoxia. Deep-basin carbonate source rocks can develop in water petroleum systems consisting of source, seal, and reservoir depths in silled anoxic basins. Prolific source rocks have been strata. Large-scale depositional fabrics have a vertical and deposited in all of these settings (Myers, 1993). The Williston lateral consistency for regional correlation, although small- Basin appears to have all of these types of source rock accumu- scale fabrics exhibit considerable variation caused mainly by lations, although there is currently not a thorough understanding secondary alteration. of the origins of Williston Basin source rocks. Carbonate depositional systems differ from clastic systems in that they create physiogeographic restrictions required for source rock deposition by building upward in response to rela- Basin Production tive sea level rise and a change in water chemistry. The car- bonate buildup of source sediment that is high in total organic Noncommercial gas production from a Dakota Sandstone carbon develops predominantly in transgressive systems tracts water well was first reported in the southeastern part of North in areas of restricted circulation between carbonate buildups Dakota in 1892 (Anderson and Eastwood, 1968). Several (Myers, 1993). Sediment deposited in shelf environments years later, shallow gas was discovered in the north-central Basin Production 13 part of the State and supplied several small towns and farms. Gas production mimics oil trends because most of the gas The oldest commercial gas production was established from is associated with oil generation. The first gas cycle started in shallow Upper Cretaceous Shannon Sandstone Member of about 1951with a steady increase until 1964 when production the Gammon Shale and Judith River Formation in 1913 in increased slightly to a peak of almost 2.5 BCFG per month. Montana in the northwest part of the Cedar Creek anticline. Subsequently a 20-percent drop in production occurred until The new discovery was quickly expanded to 11 new fields, the start of the second cycle. That cycle began with a sharp and in 1932 more than 12 billion cubic feet of gas (BCFG) production increase to about 9 BCFG per month in 1984, after was sold (Bartram and Erdmann, 1935). The first commer- which production decreased slightly and leveled off for several cial oil production was established with the 1951 discovery years. In 1996 a third cycle began with a small increase to its of the Amerada , Clarence Iverson #1 well current level of 11.9 BCFG per month. on the Nesson anticline in North Dakota. The discovery well The production cycles observed in the Williston Basin was completed in the Silurian , although could be the result of new large field discoveries from the subsequent development on the anticline focused on the discovery of large structures and by technological advances in Mississippian Madison Group. drilling and completion techniques. For example, the discov- Williston Basin production history plots indicate that the ery of oil and gas from the Nesson anticline, Cedar Creek basin has undergone three production cycles in both oil and anticline, and the Elm Coulee field resulted in the production gas (fig. 10). Initial production during the first oil cycle started of large amounts of oil and gas from the Williston Basin. Oil in about 1951 and increased to a maximum of 2.5 million price does not appear to be a major factor for large systematic barrels of oil (MMBO) per month in 1966. A slight decrease increases in oil production. occurred until the start of the second cycle in 1973, which Williston Basin production is confined to the northern increased to more than 7 MMBO per month in 1984. Sub- and western parts of the province (fig. 11), which outlines the sequently, production decreased slightly and leveled off for general area where source rocks have been buried to depths several years until 1994, when a third cycle began increasing sufficient to generate hydrocarbons. Most of the hydrocarbons slightly to its current level of 7.7 MMBO per month. produced from the Cedar Creek anticline and Canada migrated

10,000,000,000

1,000,000,000

100,000,000

10,000,000

1,000,000 Oil and gas production rates (bbl, mcf) EXPLANATION Oil production (bbl) Gas production (mcf) Cumulative oil (bbl) 100,000 Cumulative gas (mcf)

10,000 1951 1957 1963 1969 1975 1981 1987 1993 1999 2005 2011 Year

Figure 10. Diagram showing oil and gas production in the Williston Basin. Top curves are cumulative gas (red) and oil (green) production; bottom curves are monthly production of oil and gas; bbl, barrels; mcf, thousand cubic feet. 14 Williston Basin Province—Stratigraphic and Structural Framework of Undiscovered Oil and Gas Resources

49° 104° 100° !!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!! ! !! !! !!! !! !!!!!!!!! !!!!! ! !! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!! ! !!!!!!! ! !!! ! !!! !!!!!!!!!!!!!!!!! !! !!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!! !!!!!!! ! !!!!!!!!!!!! !! !!!!! ! !!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!! !! ! ! ! ! !!!!! !!!!!!!!!!! !!!!!!! !!!!! ! !!!!!!!!!! !!!!!!!!! ! ! !!!!! !!!! ! !! !! !!! ! !!!!!!!!!!!!!!!!!!!!!!!! !! !!! ! !!! !! ! ! !!! !! !!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !! !!!!!!!! !! !!!!!!! !! ! !!!!!!!!! !!!! ! !!!!!!!! ! !!!!!!!! ! !!! !!!!!!! !! !! !!! !!!!! ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! !!! !!!! !!!!!!!!!!!!!!! ! !!!!!!! ! !!! ! ! ! !! !! !!!! ! ! ! ! ! ! ! ! !! !! !! ! !!! !!!!!!!! !!!!!!!!!!!!!!!!!!!!!! !!!! !!!!!!!!!! !!!!!! !!!! ! !! !!!!!!!!!!!! !!!!!!!!!!! !!!!!!!!!! !! !!!!! !!!!!! !!! ! ! !!!!!!!!!! ! !!!!! ! !!! !!!!! ! ! !!! !!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!! ! !!!!!!! ! ! !!!!!!!!!!!!!!!!!!! !! !!!!!!!! !! !! ! !!!! !!!!!!! ! !!!!! ! ! !!! ! !!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!! !! !!!! ! !! !! !!! !!!!!!! ! !!!!! ! ! ! !!!!!!!!!!!!!!!!!!!!!!!!!!!! !!! !!!!!!!!!! ! ! !! ! ! !!!!!!!!!!!!!!!!!!!!!! ! !!!!!!!!! !!!!!! ! !!! !!! ! !!!!!! !! !!!! !! !!!! ! ! ! !! !!!!!!! ! !!!! !!!!!!!!!!!!! !!!!! !!!!! !!!!! !!!!!!!! !!! ! !!!!!!!!!! !! ! !!!!!!!!!!!!! !!! ! ! !! ! !!!!!!!!!!!! !! !!!!!!! !!! !!!!!!!!!!!!!! !!!!!!!!! !!! !! !!!!!!! !!!!!! ! !!! !! !!!!!! !!! !! ! !!!! ! !!!!!!!!!! ! ! !!! !!!!! ! !!!!!!!!!!!!!! !!!!!! ! ! !!!!!!!!!!!!!! ! !!!! ! !! ! ! ! ! !!!!! !!!!!!!!! !!!!!!!!! !!!! ! !!!!!!! !!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!! ! !!!!!!!! !! ! !!! ! ! !! ! ! !!!!!!! !!!!!!!!!! !!!!!!!! !!!! !! !!!!!!!!!!!!!!!!!!!!!! !!!!!!!! !!!!!!!!!!!!!!!!!! !!!!!!!!!!!! !!!! ! ! !!!!!!!! ! !! !! !!!!!!!! !!!!!!!!!!!! !!!!!!!!!!!!!!!!!! !!! !!! !!!!!!!! ! !!!!!!!!!!!!!!!!!!!! ! ! !! !!! ! ! !! !! !!! !!!!! !!!!!!!!!!!!!! !!!!!!!!!!!!! !!!! !! !!!!!!!!!!!!!! !! !!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!! !!!!!!!!!!!!!!!!!!!! !!! !! !! !!!! !! ! !! !! ! !!!!!!!!!!!!!!! !!!!!!! !! !! !!!!!!! !! !!!! !!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!! !!!!! !!!! ! ! ! ! !!!! !!!!!! !! !! !!!!!!!!!!!!! ! !!!! !!!!!!!!!!!!!!!!!!!!!!!!!! ! !!!!!!!!! !! !!!!!! !!! !! !! ! !! !! ! !!!! ! !!! !! !!! ! !!!!!!! !! !!!!!!!!!!!!!!!!!!!!!! !!! ! ! !! !!!! ! ! !!!!! !!! !!!! !! ! ! ! ! ! !! !!!!!! ! !!! !!! !!!!! !!!! !! !! !!!! !!!!!!! ! ! ! !!!!!!!! !! !!!! !!!!! !!! !!!!!!!!!!! ! ! !! ! !!!!!!! ! ! ! !!! ! ! !! !!! ! ! ! ! !!! ! ! !!!!!!!! ! !!! !!!!! ! ! ! !!! !!!! ! !!!! !! !!! ! ! ! !!! ! ! ! !! !!!!!! !!!!!!!!!!!! !! ! !!!! !!!!! !!!!!!! !!!!!!! !!!!!!!!!!!!!!!! ! ! ! !!!! !!! !!!!!!!!!!!!!! !! !!!!!!!! !! !!! !!!!!!!! !! !!! ! !! ! !!!!!!!!!! !!!!!!! ! !!! !!!!!!!!!!! ! ! ! ! ! !! !!!! ! ! !! !! !! ! ! !!!!!! ! ! ! !!!!!! ! ! !! ! !!!!!!!! ! ! ! ! ! ! !!!!!!!! ! !!!!!! !! ! ! !!! !!! ! !!!!!! !!! !!!!!!!!! ! !!! !! !!! !!!!!! ! ! ! !!!! !!! !!!! !!! ! ! !! !!!!! !!!! ! !! !!!!!!!!!!! !!! !!!!!!!!!!!! !!!!! ! ! !!!!!!!!!!!!!!! ! !!!! !!!!!! !!!!! !!! ! !!!!! !!!!!!!! ! !!!!!!!!!!!!!!! !!!!!!!!!!! ! !! !! !!!!!!! !!!!! !!!! !!!!!!!!!!! ! !!!!!!!! !!!!!! !!! !! ! !!!!! !!!!!!!!!!!!!!! ! !!!! !!!!!! !!!!!!!!!!! !!!!! !!!!!!!!!!!!!!!!!!!! ! ! !! ! !! !!!!!!!!!!!!!!!! !! !!!!! ! ! !!!!!!!!!!!!!!!!!!!!!!!!!! !! !!!! ! ! ! ! ! !!!! !!!!!!!!!!!! !!!!!!!!! ! !!!! !! !!!!!!!! ! ! !!!!!!!!!!!! !!!! ! !!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! !!! ! !!!!!! !!!!!!!!!!!!!!! ! ! !! ! ! ! ! !! ! ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !! !!!!! !!!!!!! !!!! !!! !!!!!!!!! !!!!!!!!!! !!! !! ! !! ! ! !!!!!!!!!!!!!!!!!!!!!!!!!!!! !! ! ! ! !! !!!! !!!!!!! !!! ! !!!!!!!!!!!!!!!!!! ! ! ! !!!!!!!!!!!!!!!!!!!!! !!! ! ! ! !!! !! ! !!! !!!!!!!!!!!!!!!!!!!!!! ! !! ! !!! !!! !!!!!!!!!!!!!!!!!!!!!!! !!!!! !!!!!!!!! ! ! !!!!! ! !! !!!!!!!! !!! ! ! !!! ! ! !!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! ! !! !!! !!!!!! !!! ! !!! ! ! ! !!!!! ! !!!!!!!!!!!!!!!!!!!!! !!!!! ! ! ! !! !! !! ! ! ! !!!! !!! !! !!!!!! ! ! ! !! !! !! !!!!!! !!!!! ! !! ! !!!! ! !!! !!!!!!!!! !!!! !!!!! ! !! !!! !!!!!! 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!!!! !!! ! ! ! ! !! !!! ! !!!!! !!!!!! ! !!!!!!!!!!!!!!!!!! !!!! !!!!!!!!!!!!!!!!!!!!!! ! !!!!!!!!!!!!!!! !!!! ! !!! !! ! !!! !! !!! !!! !!! !!!! ! !!! !!!!!!!!!! !!! ! ! !!! !!!!! ! ! !!!!!!!! !! ! ! !!! !! !!! !!!!!!!!!!!!!! !!!!!!!!!!!!! !!!!!!!!!!!!! ! !!!!!!!!!!!!! !! !! !!!!!!!!!!! !!!!!! !!!!!!! !!!! !!!!!!!!!!!!!!!!!!!!!!!!! !!! !! ! !!!!!!!!!! !!! !!! ! !!! !!!!!!!!!!!!! !!!!!!!!! !!!!!!!! ! !!!!!!!! !!!!!!!!!! !!! ! !! !! ! !! ! !!!!!!! !!!! !!! !!!!! !! !!!!! !! ! !!! !!!!! !!! !!!!! !!!!!!!!!!!!!! !!!!!!! !! ! ! ! !!!!!!!!!!!!! !!! ! !! ! !!! !!! !!!!!!! !! !!!!! !!!!! !!!!!!!! !! !!! ! ! ! ! !!!!!! ! !! !!!!!!!!!!!!!!!!!!!!!!!!!!!! ! !!! !! !!! !!!!!! ! ! !!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!! !! ! !!!!!! ! !!!!!!!!!! !!! !!!!!!!!! !!!!! !!!!!!!!!! !!!!! !!! ! ! !!!!!!!! !!!!! !!!! ! !!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !! ! !!!!!!!!!!! !!!!!!!! !!! !!! ! !! !!! !!!!!!!! !!!!!!!!!!! ! ! !!!! !!!!!!!!!! !!! ! !! ! ! !!!!!!! !!!!!!!!!! ! !!! !! !!!!!!!!!!!!!!!! !!!!!!!!!!!!! !!!!!!! !!!!!!! ! ! !! !!!! !!!! !! !!! ! !!!!! !!!! !!!!!!!!! !!!!!!!! !!! !! !! !!!!!!!!!!!!!!!!!!! !!!!!!!!! !! !!!!!!!! !!!!!!!! !! !!!! ! ! !! ! ! !!!!! ! ! !!!!!!! !!!!!!!!!! ! !! ! !!! !!!!!!!!! !!!!! ! !!! !!!!!!! ! !!!!!!!!!!!!!!!! !!! !!!! !!!! !!! !!! ! !!! !!!! !!!! !!! !!!!!!!!!!!!!! !!!! !!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! !!!!!!!!!!!!!!!!!!! ! !!!!!! !!!!!!!!!!!!!! !!!!!!!!!! !!!!!!!! ! !!!!!! !! !! ! !!! !!!!!! !! ! ! !! !!!!!!!!!!!!!!!!!! !! !! !! !!!!!! !! !!!!!! !!!!! ! !!!!!!!!!!! !! ! !!!!!!! !! !!!!!! !! ! !!!! !!! ! !! !!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !! ! !!!! !!!!!!!!!!!!!!!!! !!!!!! !!!!!! ! !! !!! !!!!! !! ! ! !! ! !!! !!!!!!!!!!!!!!!!!!!!! !!! ! !!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!! !! !!!!!!!!!!!!! !!!!!!!!!! !!!!!!!!!!!! !!!!! ! !!!!!!!!! ! !!!! !!! !!!!!!! ! ! ! !!! !!!!! ! !! !!! !!! !!!!!!!!!!! !! !!!!!!! !!!!!!!! ! ! !!!!!!!!!! !!!!!!!!!!!!!!! ! !!!!!!!!!!!!!!!!!!! ! ! ! !!!!!!!!!!!!! ! ! ! !!!!!!! !! ! !! ! !!!!! ! !!!! !!!!!!! !!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! !! !! !!!!!!!!!!!! ! ! ! !! ! ! ! !!! !!! ! ! !!!!!!!!!!! !! !!!! !!!!! !!!!! !! !!!!!! ! !!!! !!!!!!!!!!!!!!!!! !!!!!!!!!!!!!! !! ! ! !! !! ! !! !!! !! ! !! !! ! ! ! !!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!! !!!! ! ! ! ! !! ! !!!! ! ! !!! !! !! !!!!!!!!!! !!! !!!!!!!!! !!!!!!!!!!! !! !!!!!!!!!!!!!!!!!!!!!!!!! !! ! !!!! ! ! !! ! ! !!!! !! ! ! !! !!!! ! ! !! ! !!!!!!!!! !!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!! ! !! !!!! !! ! ! ! ! !!!! !! ! ! !!!!!!!!!!!!!!!!!!!!!!! ! !!!!!!!!!!!!!! !! !!!!!!!!!!!! !!!! ! !!!!! ! ! !!!!!!!!!!! !! ! ! ! !!!!! !!!!!!!!!!!! ! !!!!! ! !!!!!!!!!!!!!!!!!!!! !!! ! !!! !! ! !!!! ! !!!!!!!!!!!!!!!!!!! !!!!! !!!!!!! !!!!!!!!!!!!!!!!!!!!! ! !!!! !! ! ! ! !! ! !!!!!! ! ! !!! ! !!!!!!! !!! !!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!! ! !!!!!!! ! !!!!! ! ! !! ! ! !!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!! !!!! !!!! ! ! !!! ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! ! !! ! ! !! !! ! !! !! !!! !!!!!!!!!!!!!!! !!!!! !!!!!!! !!!!!!!!!!!!!!!!! !!!! !!!!!!!!!!!!! ! !!!! ! !! !!!!!!!!!!!!!!!!!!!!!! ! !!!!!!!! ! !!!!! ! !!!!! !! !!!!!!!!! !! !!!!!!!! !!!!!! !! !!! !!!!!! ! ! !!!! !! !! ! ! !!! !!!!!! ! !!!!!!!! !!!!! ! !! !! !!!!! ! ! ! ! ! ! !!!!!!!! !! !!!!! !!!!!!!!! ! !!!! ! !! !! ! !!! ! ! !!!! !! ! !! ! ! ! !! !!! !! ! ! ! !!!!! !!!!! !! !!!!!! !!! !! !!! ! ! ! !!! ! !!!!! !!!!!!!! ! !! ! !!!! !!!!!!!!! !!!!!! !!!! ! ! ! !!!!!!! !!! ! ! ! ! ! ! !! !!!!!!! ! !! ! !!!!!!!!!!!!!!!!!!! ! ! ! !!!! ! !! ! !!! !! !!! !! ! !!! ! ! !!!! ! !!!!! !!! ! !! !!!!! ! !! !!! ! !!!!!!!!!! !!!!!!!!! ! !! ! ! ! !! ! !! !! !! ! !!!! !! ! ! ! !! !! !! ! ! ! !! ! !!!!!!!!!!!!!!!!!!! ! NORTH DAKOTA !! !! !!!!!!!! !! ! !! ! ! !! !!!!!!!!! ! !!!!!! ! !! !!! !! !!! !!!! !!! !!! !! !!!!!! !! !!! ! !!!!!!!!!! !!!!!! !!!!!! ! !!!! ! !! ! ! !! !!! ! ! ! !!!!!!!!! ! ! !!! !! ! ! !!!!!!! !!!!! !!!!!!!!!!!! !! ! !!! !!!! !!!! ! !! !!!!!!!!!!!!!!!!!!!!!!! !!!!!! ! ! ! !! ! ! !!! ! ! !!!!!!!!! !! !!!!!!!!!!!!!!!!!!! !!!!!! ! !! !!!! !!!! !!!!!!!! !!!!!!!!!!!!! ! !!!! ! !! ! !!!! !! !!!! !!!!!!!!!!!!!! ! !!!!!! ! ! ! !!!! !!!!!! !!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!! !! !!!! ! ! ! !! ! !! !!! !!! !!!!! ! !!!!! !!!!!!!!!!!!! ! !!! ! !!!!!!!!!!! ! !! ! !!!!!!!!!!!!!!!! ! !!!!!! !! ! !! !! ! ! !!!!!!!!!! ! !!! ! ! ! !! ! !!!!!!!!!!! !!!! !!!!!!!!! !!! ! !!!!!!!!!!!!! !!! ! !!!!! !! !!! !! !!! ! !!!!!!!! ! !! ! ! !!!!!!!!! !!!!!!!!!!!!!!!! !!! ! ! !! !!!! !!! !! ! !!!! !! ! ! !!! !! ! !!! !! ! ! !! !!!!!!!!!!!! ! ! !!!!!!!!!!!!!!!! !!!! !! ! ! !!!! !! !! ! !! !!!!!! ! !!! !!! !!!!!! !!!! ! !!!!!!! !! !!!!!!!!!!! !! !! !! !!!!!!! ! !!!!!!! !!!!!! !!!! ! ! !!!!!! !!!! ! !!!! !!!! !! !!!!!!!!!!!!!!!!!!!!!!!! ! !!!! !! !!!!!! ! !!!!!! ! !!!!!!!!!!! !!!!!!!!!!!!! !!!!!!!!! ! ! ! ! ! !! !!!!!!!!!!!!!!!!!!!! !!!!!! !!!! !!! ! ! ! !! !!!!!!!!!!!!!!!! ! !!!!!!! ! !!!! !!!!!!!!!!!!!! ! ! !! !!!!!! ! !!!! !!! ! !!!! !!! ! !!!!!!!!! !!!!!! ! !! ! !!!!!!!!!!! !!!! ! !! ! !!! 47°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

! ! ! ! ! ! ! ! !! !! ! ! ! ! ! !! ! ! !!!! ! !!! ! !!!! ! !!!!!! !!!!!! !!!!! !!!!!! !!!!!! !!! !!!!!!!! !!! !!!!! !!!!!! !!!!!!!! !!!!! ! !!!!! ! !! ! !! ! !!!!!! !! ! ! ! !!! !! ! !!!!!! !!!! ! ! ! ! ! !!! !!! EXPLANATION Williston Basin production reservoirs Lower Paleozoic Bakken-Sanish-Three Forks Madison SOUTH DAKOTA Upper Mississippian-Triassic-Jurassic Cretaceous

Wyoming

0 100 200 MILES

0 100 200 KILOMETERS Figure 11. Map showing oil and gas production distribution in the Williston Basin Province; reservoirs categorized as lower Paleozoic, Bakken-Sanish-Three Forks, Madison, Upper Mississippian-Triassic-Jurassic, and Cretaceous. to these areas from deeper in the basin. Currently (2008) the assessment defined 10 TPSs and 19 AUs, which range in age cumulative production is 2,740 MMBO and 2,700 BCFG from Cambrian to Tertiary (fig. 5). The TPSs are divided into with monthly production rates of 7.7 MMBO and 11.9 BCFG conventional and continuous petroleum systems—the conven- (IHS Energy Group, 2007) coming mostly from the Madison tional systems include 9 TPSs and 13 AUs, and the continuous Group and Red River Formation reservoirs. system includes 2 TPSs and 6 AUs. The TPSs and AUs for the conventional system are mostly Paleozoic in age plus one shallow biogenic gas. The unconventional system includes a Assessment Results Bakken-Lodgepole TPS and five AUs and one Coalbed Gas TPS and AU. Assessment of recoverable resources is based on the The Williston Basin Province assessment results show concept of a TPS, which provides a framework for identify- that the mean estimate of continuous undiscovered resources ing and analyzing hydrocarbon accumulations (Klett and Le, are 3,645 MMBO, 2,730 BCFG, and 148 million barrels of this CD-ROM). Within each TPS are defined one or more AUs natural gas liquids (MMBNGL), most of which are in the that contain certain geologic characteristics and conditions Bakken-Lodgepole TPS (table 1). Estimates of undiscovered favorable for hydrocarbon generation, migration, and accu- resources in conventional AUs are 197 MMBO, 976 BCFG, and mulation. Each AU is assessed as to the quantity of techni- 54 MMBNGL, with most of the oil and gas from Ordovician, cally recoverable hydrocarbon resources. The Williston Basin Devonian, and Mississippian carbonate reservoirs. Assessment Results 15

Table 1. Williston Basin Province assessment results. [MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. For gas accumulations, all liquids are included as NGL (natural gas liquids). F95 represents a 95-percent chance of at least the amount tabulated; other fractiles are defined similarly. TPS, total petroleum system; AU, assessment unit. Gray shading indicates not applicable] Total Undiscovered Resources Total Petroleum System Field Oil (MMBO) Gas (BCFG) NGL (MMBNGL) and Assessment Unit Type F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean Bakken–Lodgepole TPS Elm Coulee–Billings Nose AU Oil 374 410 450 410 118 198 332 208 8 16 29 17 Central Basin–Poplar Dome AU Oil 394 482 589 485 134 233 403 246 10 18 35 20 Nesson–Little Knife Oil 818 908 1,007 909 260 438 738 461 19 34 64 37 Structural AU Eastern Expulsion Oil 864 971 1,091 973 278 469 791 493 20 37 68 39 Threshold AU Northwest Expulsion Oil 613 851 1,182 868 224 411 754 440 16 32 64 35 Threshold AU Coalbed Gas TPS

Continuous Oil and Gas Resources Fort Union Coalbed Gas AU Gas 368 791 1,701 882 0 0 0 0 Total Continuous Resources 702 1,422 3,645 2,730 148

Bakken–Lodgepole TPS Oil 148401320000 Middle Sandstone Member AU Gas 0 0 0 0 0 0 0 0 Oil 2 7 18 8 1 4 11 5 0 0 1 0 Lodgepole AU Gas 0 0 0 0 0 0 0 0 Winnipeg–Deadwood TPS Oil 1 4 10 5 3 9 24 11 0 0 1 0 Winnipeg–Deadwood AU Gas 56 161 358 178 3 8 20 9 Red River TPS Oil 12 29 51 30 11 28 55 30 1 3 6 3 Red River Fairway AU Gas 58 155 314 167 11 30 67 33 Oil 024200100000 Red River East Margin AU Gas 0 0 0 0 0 0 0 0

Interlake–Stonewall–Stony Oil 9 22 44 24 8 22 47 24 1 2 5 2 Mountain AU Gas 0 0 0 0 0 0 0 0 Winnipegosis TPS Oil 4 11 22 11 2 6 14 7 0 1 1 1 Winnipegosis AU Gas 0 0 0 0 0 0 0 0 Duperow TPS Oil 2 5 12 6 1 3 6 3 0 0 0 0 Dawson Bay–Souris River AU Gas 0 0 0 0 0 0 0 0

Conventional Oil and Gas Resources Oil 13 26 44 27 9 20 38 22 1 2 4 2 Duperow–Birdbear AU Gas 0 0 0 0 0 0 0 0 Cedar Creek Paleozoic Composite TPS Oil 6 19 41 20 3 12 28 13 0 1 2 1 Cedar Creek Structural AU Gas 0 0 0 0 0 0 0 0 Madison TPS Oil 13 43 85 45 9 33 72 36 1 3 7 3 Mission Canyon–Charles AU Gas 0 0 0 0 0 0 0 0 Tyler TPS Oil 4 14 31 15 1 3 7 3 0 0 0 0 Tyler Sandstone AU Gas 0 0 0 0 0 0 0 0 Shallow Biogenic Gas TPS Shallow Biogenic Gas AU Gas 48 418 1,091 475 0 0 0 0 Total Conventional Resources 197 976 54

Total Undiscovered Oil and Gas Resources 3,844 3,705 202 16 Williston Basin Province—Stratigraphic and Structural Framework of Undiscovered Oil and Gas Resources

Acknowledgments Gerhard, L.C, and Anderson, S.D., 1988, Geology of the Williston Basin (United States portion), in Sloss, L.L., ed., Valuable suggestions were given by Ron Charpentier, Geology of North America: Geological Society of America, Troy Cook, Tim Klett, Rich Pollastro, and Christopher Schenk, DNAG, Decade of North American Geology, p. 221–241. U.S. Geological Survey Central Energy Resources Assessment Gerhard, L.C., Anderson, S.B., and Fischer, D.W., 1990, Team. The report was greatly improved by technical reviews of the Williston Basin, in Leighton, from Dick Keefer and Seth Haines, USGS. The assistance of M.W., Kolata, D.R., Oltz, D.F., and Eidel, J.J., eds., Interior Wayne Husband for graphic design and Chris Anderson for cratonic basins: American Association of Petroleum Geolo- GIS management is gratefully acknowledged. gists Memoir 51, p. 507–559.

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