FORT PECK RESERVATION List of Topics

BACKGROUND Reservation Overview Regional Geologic Overview GEOLOGIC OVERVIEW Geologic History Summary of Play types CONVENTIONAL PLAY TYPES Play 1 - Folded Structure Mississippian Carbonate Play Play 2 - Ordovician Red River Play Play 3 - Devonian Nisku-Salt Collapse Play CONVENTIONAL / UNCONVENTIONAL PLAY TYPES Plays 4,5,6 - Pre-Prairie (Winnipegois/Interlake), Pre-Red River Gas, Bakken Fairway Play 7 - Cretaceous Sands-Biogenic Gas (Muddy, Judith River, Eagle) REFERENCES OVERVIEW Leasing reservations than off reservation, a net drain of tax resources is unwelcome. The The Bureau of Indian Affairs handles the leasing of Tribal and Allotted lands Tribes have recently negotiated tax revenue sharing agreements with the State of FORT PECK INDIAN RESERVATION on the Fort Peck Reservation. This occurs primarily during two sales each year, Montana affecting, gasoline, alcohol, and cigarette taxes. The Assiniboine and Sioux Tribes although negotiated leases are also permitted. The Bureau of Land Management under Federal law oversees the drilling and Fort Peck Oil and Gas Lease Sales Tribal Headquarters Poplar, Montana production. This includes all phases of the surface disturbance during drilling and Sale dates are set in accordance with Fort Peck Tribal Resolution #474-86-1 Geologic Setting Western Williston Basin production operations. Supervising environmental and cultural assessments are passed by the Fort Peck Tribal Executive Board. The Oil and Gas sales are the responsibility of the Bureau of Indian Affairs. conducted the second Thursday in March and the second Thursday in September of each year, with a minimum of forty-five (45) day advertisement. General Setting Royalty Payments The Fort Peck Indian Reservation occupies about 1,456 square miles (931,792 The Federal Minerals and Management Service handles royalty payments to acres) in Valley, Roosevelt, Daniels, and Sheridan Counties in northeastern the Fort Peck Tribes. They handle the collection of royalties from operations and CONTACT: Montana. The reservation has natural boundaries on three sides; the Missouri the payment of the money to the Bureau of Indian Affairs for distribution. Larry Monson, Geologist River on the south, Porcupine Creek on the west, and Big Muddy Creek on the Production and revenue accounting on Tribal lands (not Allotted) under joint Minerals/Tax Administration Office venture agreements, or operating agreements is handled by an independent east. The northern boundary is along the upper part of the second tier of sections Ft. Peck Tribe through township 33 N., from the east side of Range 39 E. to the east side of accounting firm other than the MMS. P.O. Box 1027 Range 55 E. The Bureau of Land Management under Federal law oversees the drilling Poplar, Montana 5925 The Fort Peck Indian Reservation is in the Northern Great Plains and phases of a prospect from site development to production. Environmental and typically has rolling uplands that are dissected by the Missouri and Poplar Rivers cultural assessments are also monitored. TEL: (406) 768-5155 ext 358 and their tributaries. The Missouri River is the largest stream in the area, flowing Companies operating on the Fort Peck Reservation are required to employ eastward at a gradient of about 1 foot per mile. The Poplar River flows south Indian people while working on trust lands. They are encouraged to do so while across the central part of the reservation to join the Missouri River at Poplar. The operating on adjacent, non-Indian lands. The maximum collectible tax is 7 altitude ranges from about 3,050 feet in the northwestern part of the reservation percent. Any revenue above 27 percent is written off as a credit against the tax. to less than 1,900 feet in the southeastern part. Payment is made quarterly to the Tribes. At this time, operators are still paying The main settlements are in the valley of the Missouri River, along U.S. all regular state and local taxes in Trust production as well. Highway 2; the largest city is Wolf Point. The largest nearby city is Glasgow, CANADA about 15 miles west of the southwest corner of the reservation. A few Post Office Contractors Business Tax MONTANA stations are in the northern part of the reservation. The Tribes also levy a tax similar to the Navajo Business Activity Tax. This is Daniels Valley 5 NORTH DAKOTA a 0.5 percent tax on the gross receipts of any contractor making more than 24 Plentywood Sheridan Standard Operating Procedures $100,000 in real improvements on Trust land. Large construction projects, The Standard Operating Procedures handbook is to assist the Oil and Gas mining and related developments, and utility construction are all liable for this 2 16 Industry with the task involved in the leasing and exploration of Indian lands. tax. Businesses wholly owned by the Tribes are exempt. Malta FORT PECK Roosevelt Due to the uniqueness and diversified management, every Tribal government 2 maintains in dealing with Mineral Development, the S.O.P. was conceived to Utilities Tax Wolf Point Culbertson eliminate any confusion in dealing specifically with the Fort Peck Tribes. A third tax, enacted in May 1987, is imposed on the property of utilities Phillips Glasgow Richland within the reservation, excluding Tribally owned entities or utilities located on The contents within the S.O.P. are not set in stone and allow for negotiations, McCone Sidney particularly in dealing with Tribal lands. Leasing of tribal lands is more flexible Tribal lands with a total value less than $200,000. Property is assessed annually 200 especially with joint venture agreements. and based on a value computed using Montana Codes Chapters 15-23. An Garfield Circle appointed three member Tax Commission arbitrates disputes over property Jordan Dawson 16 Melcher Bill valuation. The Indian Minerals Development Act of 1982, also known as the Melcher The Burlington Northern Railroad sued the Tribes over this tax, but the 59 Glendive Bill, has greatly expanded the authority of Tribes to govern the development of Federal District Court in Great Falls upheld the Tribe's power to impose the tax. 200 Prairie 94 their resources. Since the enactment of the Bill in 1982, the Fort Peck Tribes BN appealed the case to the Ninth Circuit Court in San Francisco and lost. Their Wibaux success in negotiating joint venture agreements has attracted the interest and present appeal has been taken to the U.S. Supreme Court and a ruling is pending. participation of several oil companies. Due to the trust status of Indian Reservations, various tax incentives have given the Fort Peck Tribes authority in Uses of Revenue offering oil companies part interest in operations or revenue sharing agreements. All revenues received from the three taxes go to the Tribal general fund. At This has given the Tribes greater flexibility with greater financial returns. present the issue of dual taxation by both State and Tribes is of great concern. The Cotton Petroleum case decided both States and Tribes have the authority to tax natural resource production. When poverty and unemployment are higher on

Fort Peck Reservation RESERVATION OVERVIEW Page 1 of 13 Montana Alberta Shelf CANADA 98 97 Wakea 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 Hogeland Bowdoin D A N I E L S Dome BF Bearpaw UNITED STATES Nielson S H E R I D A N Sweetgrass Arch Basin Reserve 2 Uplift -300 Bredette Poplar -200 -700 OpheimNose Syncline Poplar FaultDome -100 Hinsdale Fault FP -600 -1200 A A' +100 -500 0 Nesson

Anticline

Little -400 -1000 Judith Rocky Mtns N. Lustre -1100 Mtns Blood NORTH SynclineCreek FORT NE Benrud Big Weldon-Brockton FaultCedar Creek BERTHOLD DAKOTA E. Benrud W LC Little Snowy Anticline Belt Mtns Cat Creek Fault V A L L E Y - 800 Volt -1300 Mtns - 600 -1400 Wheatland Summatra Williston Basin R O O S E V E L T MONTANA Porcupine Poplar Dome Syncline Lustre -1500 Willow Creek Fault Dome Miles City Wolf Creek Nose -1600 Crazy Bull Arch Tule Creek East NW Poplar Mountains Tule Crk Mountains Basin STANDING Lake Basin Fault ROCK Basin South Tule Crk Nye-Bolwer Fault Powder 0 Brockton-Froid Beartooth Mtns Palomino - 400 Pryor Oswego Nose Fault Zone Mtns. River - 200 -400 - 500 Yellowstone BIGHORN MTN - 100 Bighorn Basin E. Poplar

SOUTH - 500 Snake Black - 600 - 1700 OVERTHRUST Absaroka River Mtns DAKOTA - 200 - 1300 - 1500 Basin WYOMING Hills - 300

Owl Creek Laramie Uplift Mtns Casper Wind RiverWind Mtns Arch Mtns. River EXPLANATION FORT PECK INDIAN RESERVATION BELT Basin Fault Choctaw Arch IDAHO Casper Mtn Charles Oil Fields Sweetwater Detailed Structure and Laramie Nisku Oil Fields Production Map Green Uplift Hartville Mtns Red River Oil Fields River Hanna Basin Red Laramie NEBRASKA Greenhorn Structure Basin Alliance Rock Desert Basin Springs Medicine Basin Uplift Basin Bow Mtns UTAH Sierra Figure FP-2.2. Structure map of the Greenhorn Formation and Fort Peck Reservation boundaries. Shows production information regarding Uinta Mtns. Washake Madre position and play type. Basin COLORADO Play Types Encountered EXPLANATION PRESENT DAY Within Reservation Area Anticline Precambrian Basement Uplifts STRUCTURAL FEATURES Syncline Rocky Mountain Region Conventional Other Uplifts or Basins 1. Mississippian Carbonate Structure Cenozoic Volcanic Fields Faults Figure FP-2.1. Present day structural uplifts and basins, Fort 2. Ordovician Red River A A' Peck Reservation and location of regional cross-section A-A' 3. Devonian Nisku Salt Collapse Reservations Cross-Section (modified after Peterson, 1987). 4. Winnipegosis and Interlake

Regional Geology Fault system trends Northeast to Southwest and is one of the major lineaments in Unconventional The Fort Peck Reservation is situated on the western flank of the Williston Basin the Williston-Blood Creek structural system. Minor structural features include 5. Pre Red River Gas (Winnipeg/Deadwood) (Fig. FP-2.1). The basin is predominantly a carbonate depocenter interbedded the Wolf Creek Nose, the Oswego, the Bredette Nose and the Opeim Syncline. 6. Fractured Bakken Play with clastics and evaporites. The clastic units are composed of both marine, 7. Judith River and Eagle Sandstones Biogenic Gas organic rich shales, which are the principle source rock, and marine or fluvial Geologic History sandstones. The carbonates and evaporites are mainly tidal flat, bioherm / reefs A generalized structural cross-section (see cross-section A-A', FP-3.1) has been or sabhka deposits. Cyclic sedimentation of marine shales, limestone and constructed to summarize present day tectonic provinces and older paleostructure. dolomites and anhydrites / salts are typical of the Paleozoic section. Reservoir The cross-section uses rock thickness values from each of the geologic periods. rock can be formed in the limestone or dolomite with both primary and secondary The section runs along the 48 degree latitude line and values were selected at one porosity. Porosity may be intergranular, vuggy, intercrystalline or fractured, degree longitude intervals. depending on the rock type and depositional environment. The western end of the section, near the Blackfeet Reservation is dominated by high relief (> 5000 feet). The Cretaceous and older Paleozoic section is about Structural Geology 11,000 feet thick. Major basement uplifts, such as the Sweetgrass Arch and The Fort Peck Reservation is dominated by the Eastern Flank of the Bowdoin Bearpaw Uplift, influenced sedimentation throughout geologic time. Dome and the northwest trending Poplar Dome (see Fig. FP-2.2). The Poplar The eastern side of the cross-section is dominated by the Williston Basin, a Dome is west of the basin hinge axis which separates the Williston Basin from stable cratonic basin which comprises more than 15,000 feet of sediments. The the Bowboin Dome; both features are of Laramide age. The Brockton-Froid Fort Peck Reservation is located west of the depocenter on a shallow shelf.

Fort Peck Reservation GEOLOGY OVERVIEW Page 2 of 13 Montana Structural, Historical Geology Blackfeet A Longitude Values (In Degrees) A' 4 2 Fort Peck Reservation 6 0 West East 10 2 114 Ft. Belknap 12 Ft. Peck 0 113 112 111 110 109 108 107 106 105 104 103 102 101 100 A 15 6000 Ft. A' Berthold 0 5000

Early Tertiary Intrusions 10 Bearpaw Uplift 10 4000

Little Rocky Mountains 4 3000 NORTH 8 Poplar Dome DAKOTA 15 2000 Standing Rock Upper Cretaceous SOUTH Rocks 12 DAKOTA 6 Tertiary Rocks 10 8 8 1000 Niobrara and Eagle Fort Union and Golden Valley 2 0 10 MONTANA 10 WYOMING 0 0

Upper Cretaceous EXPLANATION - 1000 Rocks - 1000 Elevation (in Feet) Lower Cretaceous Rocks Lower Cretaceous Cambrian and older rocks 12 Niobrara and Eagle exposed at land surface Mowry Kootenai - 2000 - 2000 Sandstone Facies Shale, Sandstone and Minor Jurassic Rocks Limestone Facies 0 - 3000 - 3000 Green Shale Facies Jurassic Rocks Mississippian Rocks Oil Field, Cambrian NEBRASKA - 4000 Reservoir Triassic Rocks - 4000

- 5000 Permian Rocks - 5000 Figure FP-3.1. Thickness of Deadwood and equivalent rocks. Blackfeet Reservation, location of analog fields Cambrian Rocks Devonian Rocks and location of regional cross-section A-A" (modified after Peterson, 1987). Sands and Shales - 6000 - 6000 PreCambrian Rocks Pennsylvanian Cambrian Rocks Rocks Sweetgrass Arch Sands and Shales - 7000 - 7000 To better illustrate the geologic history of the region, which has been Montana and the Dakotas. The major source of coarse-grained clastics Rocky Mountain Trench Mississippian Rocks Overthrust Belt - 8000 influenced by all of these tectonic provinces, a series of paleo cross- was to the east (from the Sioux Arch) and graded into shales and - 8000 Bakken Shale sections are shown. Each section summarizes a particular time interval; limestones to the west. Thickness of the Cambrian varies from over 2000 Cambrian and older rocks, Ordovician to Triassic and Cretaceous to feet in the Montana Disturbed Belt to less than 100 feet thick at the - 9000 - 9000 Jurassic. Since Tertiary sediments are present only in the Williston eastern edge of the Williston Basin. Cambrian rocks at the Fort Peck Devonian - 10,000 Rocks Generalized Cross-Section A-A' - 10,000 Basin, no paleostructure section is shown. All the paleo-cross sections Reservation are about 500-700 feet thick. There is no evidence of Poplar Prairie Salt are drawn along the line of section A-A' indicated in figure FP 3.1. and Bowdoin domes at this time. - 11,000 Present Day Structure Silurian Rocks - 11,000 A paleo-cross section attempts to show what the subsurface geology Line of Section along 48 degrees of latitude with Cambrian Rocks Ordovician - 12,000 selected points every 1 degree of longitude. may have looked like within a particular time interval; no older rocks are Sands and Shales Rocks - 12,000 Datum : Sea Level Scale : 1 deg = about 50 miles illustrated. The rock units above the interval have not yet been - 13,000 Nesson deposited; so the top of the section is the datum. The datum is flat, Anticline - 13,000 Williston Basin representing the paleo ground surface. Longitude Values (in degrees) West A Ft. Peck Reservation A' East Figure FP-3.2. Generalized cross-section A-A', present day structure.

Present Day Structure 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 Figure FP 3.2 illustrates the main structural features along the line of 0 Cambrian PreCambrian Rocks section A-A'. Across the Fort Peck Reservation the main features include Cambrian Sands and Shales 1000 Sands and Shales Poplar Dome and the Brockton-Froid Fault system. The reservation is Sweetgrass Arch situated along the shallower western flank of the Williston Basin. 2000 Bearpaw Uplift PreCambrian Rocks Poplar Dome Williston Basin Cambrian to Older Rocks 3000 Rocky Mountain Trench During Cambrian time, a major seaway existed in western Montana Little Rocky Mountains 4000 and eastern Idaho ( Figure FP-3.3 and isopach of Cambrian rocks in FP Overthrust Belt Generalized Cross-Section B-B' Cambrian and Older Rocks

3.1). This seaway gradually transgressed from west to east across eastern Thickness of Sediment (feet) 5000 Line of section along 48 degrees latitude with selected points every 1 degree of longitude. 6000 Datum: Base of Ordovician

Figure FP-3.3. Generalized paleostructural cross-section' showing Cambrian and older rocks. Line of section along A-A'.

Fort Peck Reservation GEOLOGY OVERVIEW Page 3 of 13 Montana Geologic History Ordovician to Triassic Rocks A smaller depocenter of Mississippian rocks exists west of Longitude Values (in Degrees) From late Cambrian through most of the Paleozoic, the the Sweetgrass Arch and Bearpaw Uplift which were positive WEST A Ft. Peck Reservation A' EAST Williston Basin on the east side of the cross-section was the features in Mississippian time. Total thickness of Mississippian dominant receiver of sediments (see, Figure FP-4.1). The 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 rocks within reservation boundaries is about 1500 feet. All 0 Williston Basin has been a stable, shallow marine shelf through Mississippian rocks are thermally mature. Triassic Rocks Pennsylvanian Rocks most of the Paleozoic era. Ordovician and Silurian rocks were Exposure at the end of Mississippian time led to widespread Bakken Shale Permian Rocks 1000 deposited in a tidal flat environment with alternating cycles of erosion, karstification and unconformity development. Devonian Rocks limestone / dolomite, marine shales and evaporites. At the end Pennsylvanian sediments are confined to the center of the 2000 Mississippian Rocks of Silurian time, a regional unconformity extended across the Williston Basin in central Montana, south of the Reservation. Bearpaw Uplift Williston Basin and to the west. Present thickness of Ordovician Tyler sands and shales are present in the Williston. 3000 PreCambrian Rocks Sweetgrass Arch Cambrian Rocks Bakken Shale and Silurian rocks on the Fort Peck Reservation are 500 feet and Pennsylvanian rocks are about 100 to 200 feet at Fort Peck. Sands and Shales 200 feet, respectively. Apparently Bowdoin Dome and Poplar Permian deposits are confined to the central Williston Basin Rocky Mountain Trench Dome, if they existed, are poorly expressed features. Ordovician Rocks and are predominantly sand/shale and evaporite sequences. 4000 Deposition during Devonian time was similar to that during Overthrust Belt Little Rocky Mountains Prairie Salt Major erosion at the end of Permian time has removed any Ordovician and Silurian time. Within the Reservation evidence of these rocks west of longitude 104 degrees; hence 5000 Generalized Cross-Section A-A' Poplar Dome boundaries, Devonian rocks are about 1700 feet thick and none are present on the Reservation. Triassic rocks are present, Triassic through Ordovician Silurian Rocks include the regional Souris River (200 feet or less), and the but apparently pinch out within the Reservation boundaries. 6000 Thickness of Sediment (in ft) Line of cross section along 48 degrees Bakken Shale (50 to 75 feet thick) formations (see Figure FP Work by Shurr and Monson (1995) indicate that Bowdoin and latitude with selected points every 1 Cambrian Rocks degree of longitude Sands and Shales 4.2). The Prairie Salt was dissolved out of the section near the Poplar Domes were positive features. 7000 DATUM: Base of Jurassic - Permian missing western edge of the basin (near 105 degrees longitude), and Ordovician Rocks forms the structural traps within the Nisku Formation. Details 8000 of Nisku trap formation are discussed in Play 3, Devonian Nisku Williston Basin Canada Carnduff section of the Atlas. Bakken Shale is organically rich and is Elmore North Dakota Figure FP-4.1. Generalized paleo-structure cross-section. Line of section along 48 degrees of latitude with selected points every thought to be the prime source rock for Mississippian U.S.A. 1 degree of longitude. For location of A-A', refer to Figs. FP-3.1 and FP-4.1. production. Mouse River By Mississippian time, the Williston Basin to the west was Burke Park Bottineou continually depositing limestones and evaporites in a shallow, Renville 110 105 100 marine shelf environment. Cyclic changes in sea level produced 50 100 shoreline trends in the carbonate intervals (see Figure FP 4.3). Lake 25 Most of the producing reservoirs in the Williston Basin area are A Darling 0 75 50 A' from these cyclic marine shales, limestones / dolomites and evaporite seal sequences. Eventually, the Charles Salt would cover the entire basin and part of eastern and central Montana. By late Mississippian time, deposition was mainly of shales and Lone Ward McHenry 25 Tree Ft. Peck 0 mudstones confined to the Central Williston Basin and the Big Reservation 0 Mountrail North Dakota Snowy Trough in central Montana. Detailed field studies of Poplar Dome indicate that production is from the Charles A and Wabek B zones and reservoir rock is not plugged with salt crystals. Montana Plaza Sherwood This could be due to either salt dissolution or lack of evaporite Shoreline deposition, implying that Poplar Dome has always been structurally positive. Lucky Mound McLean Centennial Index Map 0 12 24 Mississippian or miles older ricks exposed 25-50' thickness South Dakota of Bakken Formation Wyoming 50-100' thickness miles 0 100 200 Study of Bakken Form. Area

< 100' thickness of 0 Bakken Fm 100 kilometers North Dakota

Figure FP 4.2 - Map showing thickness of Bakken Formation, location of reservation, and location of regional cross-section A-A' (modified from Peterson, 1987). Figure FP 4.3 - Mississippian Sherwood shoreline trend and position of major oil fields (after Sperr, et al, 1993).

Fort Peck Reservation GEOLOGY OVERVIEW Page 4 of 13 Montana Geologic History East West Ft. Peck Reservation A Longitude Values (in Degrees) A' 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 0 Jurassic to Cretaceous Rocks In Jurassic time, the Williston Basin was still the major depocenter for clastic 1000 Volcanics Upper Cretaceous and marine/evaporite sediments. Thickness of Jurassic rocks is estimated to be about 1000 feet thick and shows evidence of thinning at Bowdoin and Poplar 2000 (Niobrara and Eagle Rocks) Domes (Fig. FP-5.1). A tectonic structural reorganization of the North American continent occurred 3000 during Jurassic-Cretaceous time. This resulted in a major change of depocenter Lower Cretaceous (Kootenai) position in the Williston Basin; shifting from the east to the western side (refer to 4000 Lower Fig. FP-5.1). The initial pulses of the Sevier and later Laramide thrusting Cretaceous (Mowry) Jurassic Rocks resulted in dominantly clastic deposition in the Cretaceous Seaway during this 5000 time. Early Cretaceous (lower Kootenai) rocks are about 200 feet thick within the Reservation. The lower Early Cretaceous environment is thought to have 6000 been continental with deposition of fluvial sediments. Source area for these Poplar Dome deposits (i.e. Lakota Formation) is thought to have been to the southwest in Mississippian and Williston Basin Thickness of Sediment [in feet] 7000 Older Rocks Montana and south into Wyoming. Late Early Cretaceous (Montana Group-Mowry / Skull Creek strata) are Generalized Paleostructure Sweetgrass Arch Bearpaw Uplift 8000 Cross-Section A-A' about 400 to 500 feet thick. These rocks were deposited as a transgressive Rocky Mountain Trench Little Rocky Mountain marine sequence that extended from western Montana eastward into the Dakotas CRETACEOUS AND OLDER ROCKS Overthrust Belt and from Texas into Canada. The fluvial and marine sands, such as the Line of Section along 48 degrees latitude with Muddy/Newcastle are present in this interval. selected points every 1 degree of longitude Upper Cretaceous rocks are more than 3500 feet thick in the reservation area Datum: Top of Cretaceous and consist of calcareous siltstones, thin limestone intervals, and calcareous shale (Fig. FP-5.2). Extensive Greenhorn / Niobrara chalks were deposited in the Williston Basin and southeast into South Dakota, Nebraska and Colorado. The Figure FP-5.1. Generalized paleostructure cross-section A-A', Jurassic to Cretaceous Rocks (after C.W. O'Melveny, 1996). Eagle and Judith River Formations were deposited as nearshore marine and barrier island sands.

112 110 Tertiary and Younger Rocks 108 Canada 106 104 102 Tertiary time saw the erosion of older Cretaceous rocks. Swamps exsisted in 49 United States Paleocene and Eocene time in the central Williston Basin, and formed coal. By the end of the Eocene, most of the older highlands had been eroded away. Only Non Fort Peck about 350 feet of Tertiary and Quaternary sediments exist at Fort Peck. Marine Quaternary time was a period of major continental ice sheets extending into 48 North Dakota and Montana. Alpine glaciers exsisted in Montana's western Rocks mountains. Extensive glacial lakes were present along the ancestral Missouri River and its tributaries. Ice sheets covered the present day Fort Peck Reservation.

47

Legend for Facies Map (after Rice and Shurr, 1980)

non marine rocks North

coastal sandstones Dakota 46 interbedded shelf sandstones and shales

siltstones and shales

chalk and limestone South Montana Dakota 45 Figure FP 5.2 - Regional distribution of diagenetic and 0 50 miles Wyoming petrophysical facies of the Niobrara. Area within 3000 feet or less of burial should contain chalks with porosity greater 50 kilometers than 35%. Areas between 3000 to 4000 feet of burial should average 30-35% porosity (after Rice and Shurr, 1980). 44

Page 5 of 13 Fort Peck Reservation GEOLOGY OVERVIEW Montana Regional Geologic History WEST EAST PLAY TYPES - Explanation

Schematic Diagram of Play Types Fort Peck Reservation 1 - Mississippian-Madison Charles Structure Play

2 - Ordovician Red River Play

3 - Devonian Nisku/Duperow Salt Collapse Play Cretaceous 7 4 - Silurian Interlake Play

7 5 - Pre-Red River Gas Play Jurassic Winnipeg/Deadwood

Mississippian 6 - Fractured Bakken Play Mission Canyon 1 1 7 - Shallow Biogenic Gas Charles Devonian Bakken 6 6 3 Sandstone Limestone Duperow 3 Silurian 4 Organic Shale Dolomite 4 2 Shales,sandstone Precambrian Ordovician Red River 2 and siltstones Interlake Basement Cambrian Winnipeg Gas 5 Unconformity Deadwood 5 Oil

Bowdoin Dome Poplar Dome Gas-saturated Precambrian No Scale - Drawing is approximate width of Reservation sandstone lense

Figure FP-6.1 - Schematic diagram of play types within the Fort Peck Reservation. No scale implied, thickness of stratigraphic section and size of traps only shown in a relative sense.

Reservation: Fort Peck Total Production ( by province-1996) Williston Basin Undiscovered resources and numbers of fields are Geologic Province: Western flank of Williston Basin Oil: 1496 MMBO for Province-wide plays. No attempt has been made Province Area: Williston Basin (143,000 sq. miles) Gas: 1735 BCFG to estimate number of undiscovered fields within the Reservation Area: 3271 sq. miles (2, 093, 318 acres) NGL: 192 MBNGL Fort Peck Reservation USGS Play Type Description of Play Oil or Gas Known Accumulations Undiscovered Resource (MMBOE) Play Probability Drilling depths Favorable factors Unfavorable factors Designation Field Size (> 1 MMBOE) min, median, mean (chance of success)

Mississippian Structure 3101 folded structures, primary Both 878 MMBO estimated 600 MMBO (30 fields @ 20MMBO) 1 5,000 - 6,000 ft 1) confirmed play; excellent 1) production confined to and secondary porosity 916.5 BCFG not estimated production within reservation structures or structural noses in carbonates 77.9 MMBNGL Field Size (>1 MMBOE) 2) thermally mature source rocks 2) source rock immature on 2 MMBO 20 MMBO 5.3 MMBO in portion of reservation flanks of basin 1 # of undiscovered fields (> 1 MMBOE) 3) source rocks and reservoir present 3) porosity can be salt plugged 9 (min) 30 (median) 60 (max) 31.9 (mean) 4) seismic delineation is useful

Ordovician Red River 3102 Cyclic evaporite/ carbonate Both 192.3MMBO estimated 250 MMBO (25 fields @ 10MMBO) 1 10,000 - 11,500 ft 1) confirmed play; production within 1) lack of deep well control play sequence, structure/stratigraphic 586.7 BCFG Field Size (>1 MMBOE) not estimated reservation 2) current production east side updip pinchout, multiple shoreline 74.5 MMBNGL 2 MMBO/10 BCFG 10 MMBO/35 BCFG 2.1MMBO/11.7 BCFG 2) thermally mature source rocks of reservation cycles. Small, fault block structures 3) source rocks and reservoir present 3) possible small target size # of undiscovered fields (> 1 MMBOE) 4) seismic delineation is useful 2 5 (min) 25 (median) 50 (max) 26 (mean)

Mid-Upper Devonian 3103 Cyclic evaporite/ carbonate Both 164.2 MMBO estimated 250 MMBO (25 fields @ 10 MMBO) 1 7,000 - 8,000 ft 1) confirmed play; production exists 1) difficult targets to identify Nisku/Duperow Play sequences. Salt collapse structures. 169.5 BCFG Field Size (>1 MMBOE) not estimated on reservation 2) small areal extent, may Excellent porosity and permeability 13 MMBNGL 2 MMBO/10 BCFG 10 MMBO/60 BCFG 2.1 MMBO/13.1 BCFG 2) thermally mature source rocks be difficult to explore for # of undiscovered fields (> 1 MMBOE) 3) source rocks and reservoir present and may be excellent in quality 3 9 (min) 25 (median) 60 (max) 26.9 (mean) 4) seismic may be very useful

Figure FP-6.2. Play summary table containing resource information on all play types

Page 6 of 13 Fort Peck Reservation Montana Play Types Total Production Undiscovered resources and numbers of fields are Reservation: Fort Peck ( by province-1996) North Central Montana Disturbed Belt for Province-wide plays. No attempt has been made Geologic Province: North Central Montana, Sweetgrass Arch, Montana Disturbed Belt Oil: 440 MMBO to estimate number of undiscovered fields within the Province Area: North Central Montana (62,500 sq. miles), Thrust Belt (41,400 sq. miles) Gas: 1.1 TCFG 6 BCFG Fort Peck Reservation Reservation Area: 2385 sq. miles (1,525,712 acres) NGL: 192 MBNGL 33,000 BNGL

USGS Play Type Description of Play Oil or Gas Known Accumulations Undiscovered Resource (MMBOE) Play Probability Drilling depths Favorable factors Unfavorable factors Designation Field Size (> 1 MMBOE) min, median, mean (chance of success) Silurian Winnipegosis 3105 Cyclic evaporite / carbonate Both 55.5 MMBO estimated 225 MMBO (15 fields@ 15 MMBO) 1 8,000-12,500 ft. 1) confirmed play; production 1) lack of deep well control and Interlake sequences; eroisonal surfaces. 179 MMCFG Field Size (>1 MMBOE) not estimated exists on Reservation 2) production at this time on Primary and secondary porosity. 24.8 MMBNGL 3 MMBO / 15 BCFG 15/90 3.3/19.7 2) source and resevoir northwest corner of Structural/ unconformity traps. For detailed production No of Fields (>1 MMBOE) 3) thermally mature reservation Occurs as multi-pay zone with see individual play 5 (min) 15 (median) 25 (max) 15 (mean) 4) structure detected on seismic 4 Red River descriptions

Pre-Red River Gas estimated 50 BCFG (5 fields @ 10 BCFG) Ordovician Winnipeg / 3107 Sand / shale sequences. NGL No information available. Field Size (>1 MMBOE) 1 10,000-16,000 ft. 1) confirmed play; production 1) lack of deep well control Fluvial and nearshore and Low For detailed production, 10 BCFG 25 BCFG 13.1 BCFG not estimated exists near Reservation 2) low BTU, contains nitrogen Cambrian Deadwood blanket sands. Large, faulted BTU gas see individual play No of Fields (>1 MMBOE) 2) source and reseroir structures descriptions 1 (min) 5 (median) 20 (max) 7.3 (mean) 3) thermally mature 4) structure detected on seismic 5

Fractured Bakken 3112 Organic rich shale; marine Both No information available. Not estimated 0.7 7,500-11,100 ft. 1) source and reservoir 1) lack of deep well control Outlying Play siltstone; fractured; Thermally 70.3 MMBO / sq. mi. 56.24 MMCFG / sq. mi. 0.1 2) thermally mature mature oil shale. Area of play 8185 sq. mi. 3) structure and flexures exist 7806 sq. mi. untested 4) seismic can probably locate 6 structural trends

Judith River and Not estimated 3113 Niobrara Limestone and other Biogenic Gas Only production to date is 180 MMCFG / 160 acres median 1 500-4,500 ft. 1) large volume play 1) lack of reservoir may be a Eagle sandstones 2811 shallow reservoirs self-sourced; Cedar Creek Anticline and 256 MMCFG / 160 acres mean 0.70 2) shallow drilling depths problem Biogenic Gas Porosity decreases with Biogenic Gas Bowdoin Dome Area of Play 55,000 sq. mi. 3) accumulations in structural 2) may be small increasing depth. Large These fields are from Eagle 20,000 sq. mi. untested (median) traps; seismic can probably 3) lack of deep well control (Medium Potential) accumulations and Judith River sands 29,958 sq. mi. untested (mean) locate possible. 4) gas shows on Reservation 7

Figure FP-7.1 - Summary of play types (continued).

Conventional Play Types Unconventional/Hypothetical Play Types

Fort Peck Reservation Page 7 of 13 Montana Play Types (continued) PLAY TYPE 1 Analog Fields (* denotes fields lying within the Reservation) Folded Structure Mississippian Carbonate Play

(1975) Reagan Field 77,563 BO 1 well General Characteristics- The Mississippian Madison Charles is a structural- (1982) Lustre 5.9 MMBO 41 wells R 50 E R 51 E (1983) Lustre, North 179,000 BO 1 well stratigraphic play and is the primary producer on the Fort Peck Reservation. The (1985) Midfork 324,000 BO 5 wells Charles is subdivided into several producing zones (see type log) by gamma ray (1992) Nielson Coulee 112,500 BO 1 well marker and porosity zones. These zones are overlain by evporite or shale seals. The (1952) Poplar East 46 MMBO 46 wells (1952) Poplar, NW 3.9 MMBO 26 wells Charles Salt is a regional evaporite seal which overlies most of the Madison rocks. (1987) Reserve 2 194,000 BO 1 well Most of the Charles production is confined to structural domes such as Poplar (1964) Volt 3.4 MMBO 4 wells Dome, or to smaller structural noses with up-dip porosity pinchouts. Tilted 15 14 13 18 17 hydrocarbon columns are present indicating a moderate-strong hydrocarbon drive in

T the southcentral part of the reservation area. 29 Reservoir rocks are dolomitized carbonates which are either algal, oolitic, N crinoidal, or micritic deposits. Source rocks are both the organic rich, Bakken Shale

23 24 19 20 21 marine shales within the evaporite-carbonate cycles. Source rocks are thermally mature in the center of the basin and immature on the flanks. Onset of oil migration is thought to have been during late Cretaceous time.

26 29 30 29 28 R 46 E

-4680

-4660 -4640

31 32 -4600

TABLE FP-1. Poplar East Field Parameters

Formation: Mississippian Charles B -4560 -4600 Lithology: Limestone, fossiliferous, fragmental. Lower T 3700 zones can be dolomite, very fine to crystalline to -4620 30 3600 dolomitic mudstone. N -4640 Other Shows: Production exists within the Charles "A" and "C" zones. Production also develops in the -4660 Mississippian Heath and Devonian Nisku 11 Formations. Shows have been recorded in the -4680 3500 Kibbey Formation and in the Cretaceous Judith River sands. -4700 Poplar East Field Type Log (after Monson, 1995) 3000 Correlation Resistivity Porosity Seismic Average Depth: 5700 ft VOLT FIELD GR MSFL RHOB DT ROOSEVELT COUNTY, MONTANA (GAPI) (OHMM) (G/C3) (USEC/FT) Porosity: 12% gross, intergranular, vuggy 6.0 16.0 0.2 2000.0 2.0 3.0 140.0 40.0 15 14 13 Permeability: 8 md STRUCTURE MAP 5300 TOP NISKU POROSITY Oil/Gas Column:Variable, oil/water contact is tilted 10 to 20 feet T C.I. : 20 ft Charles 5350 per mile. Column to the north 28 5400 N Average Net Figure FP-8.2. Volt Field Structure Map with top Nisku porosity zone as datum (after Pay Thickness: 24 feet 5450 Reeves, 1985). 21 22 23 24 19 20 5500 The field is approximately 10 miles long and six miles wide, and TABLE FP-2. Volt Field Parameters 5550 has an anticlinal closure of 18,000 acres.

5600 Formation: Mississippian Charles

5650 Lithology: 40 feet of limestone and dolomitic 28 27 26 25 limestone;intercrystalline to cryptocrystalline 5700 and microcrystalline porosity Ratcliffe 5750 Other Shows: Devonian Nisku Both Charles and Nisku production are 5800 EAST POPLAR FIELD Mission structurally controlled, although the Charles Canyon Roosevelt County, Montana 5850 has a stratigraphic component. B-1 STRUCTURE MAP Average Depth: 5900 ft Porosity: 13% average Permeability: 0.1 md, with numerous vertical fractures Figure FP-8.1. Poplar East Field Structure Map, 50' contour interval (after Brunson, 1985). Oil/Gas Column: unknown Average Net variable Pay Thickness:

Fort Peck Reservation CONVENTIONAL PLAY TYPE 1 Page 8 of 13 Montana Folded Structure Mississippian Carbonate Play R 55 E R 56 E

CENEX 11330 31X-17 FOLSOM 110 105 PLAY TYPE 2 Blackfeet Ordovician Red River Play 13 18 17 16 15

Ft. Belknap300 A Ft. Peck N o r t h D a k o t a General Characteristics - The Red River is the second most productive CENEX 300 Ft. A' 31-20 CHRISTENSEN 100 Berthold 500 formation in the Williston Basin. Reservoirs are dolomites and 11257 500 700 300 100 -8800 dolomitic limestones formed from bioclastic mounds, and tidal flat CENEX 24 19 23X-20 UNIT20 21 22 deposits. RESERVE FIELD GULF 1-21-3C STRAND GULF DELINEATED AREA 1 STRAND Major accumulations are found on structural noses such as Nesson 11400 M o n t a n a 11380 T and Cedar Creek Anticlines. Smaller fields are found in fold structures CENEX HOUSTON CENEX PUBCO 1-28 WILLIAMS 21-29 FOLSON 4-28 ANGVICK 33 Standing Rock 41X-29 GULF draped over basement fault blocks, or small, carbonate mounds (see 1 BREKKE N 11322 300 6-28 ANGVICK Figures FP-9.1 & 9.3). Most of the production is on the extreme eastern CENEX HICKERSON 24 3043X-30 NELSON 29 1 ANGVICK 27 side of the Fort Peck Reservation. PATRICK S o u t h Da k o t a 1-27 HOLMBARD HOUSTON 16-30 NELSON 4-29 NELSON 11450 500 Source rocks are thermally mature to overmature at the basin center, 34-28 WILLIAMS 100 11337 ENERGETICS 41-31 HANCOCK Approximate limit of and pinch out on the basin flanks. Winnipeg and Red River shales are DOME Explanation CENEX 11210 the Red River Fm. 22-31 ANGVICK 2-34 WILLIAMS 300 thought to be the primary source rocks. Hydrocarbon generation and 11448 Ordovician or older SUNMARK 11179 rocks exposed at W y o m i n g 1-36 STATE land surface migration are estimated to have begun in late Paleozoic time. 32 33 34 PATRICK Thickness in feet of 1-34 WILLIAMS 300 - 9000 11438 Red River Formation N e b r a s k a Dolomite facies CENEX CENEX 6-4 PEDERSEN 3-SHORT MOSBACHER 1 NELSON -8900 Limestone and Dolomite facies Wakea Field 11500 Oil field, Red River reservoir 5 4 3 2 MOSBACHER 2 1 6 1 LODAHL 11539 Figure FP-9.2. Approximate thickness of Ordovician Red River Formation within the Williston Basin and CENEX MURRAY 1 13-3 ANDERSON T surrounding areas, Fort Peck Reservation, Analog Fields and location of Regional cross-section A-A' (modified 8680 SUNMARK 32 after Peterson, 1987). SUNMARK 1 LARSON 1 ANDERSON N 8660 MEIDSNESS 8 9 10 11 12 Analog Fields ( * denotes fields lying within the Reservation) 12 7 -9000 - 9100 11 CHASE DJ MURRAY JJ R 56 E (1987) Reserve Field 194,000 BO 1 well OIL WELL (1983) Wakea Field 2.4 MMBO 7 wells 11225 TD RESERVE FIELD ABANDONED OIL WELL SHERIDAN COUNTY, MONTANA CI=20'

DRY HOLE STRUCTURE ON RED RIVER (ORDOVICIAN) Correlation Resistivity Sonic GR MSFL DT 0 100 0.2 2000 80 40 Figure FP-9.1. Reserve Field structure map (after Ames, 1985). Table FP-2. Wakea Field Parameters DPHI 0.3 -0.1 TABLE FP-1. Reserve Field Parameters 10550 Formation: Ordovician Red River Formation: Ordovician Red River Lithology: Lithology: Sucrosic dolomite Red River "A", dense dolomite fractured on Average Depth: 10,700 ft 10600 top of structure; "B" - locally continuous, fine sucrosic dolomite; Porosity: 14% A "C" - isolated pods of fine sucrosic dolomite; Permeability: no information "D" - discontinuous layers of fine to medium 10650 dolomite. Oil/Gas Column: no information B Average Depth: Red River zone Average Net Pay Thickness: 6 feet "A" through "D" varies from 10700 11,040 feet to 11,280 feet Other Formations with Shows: no information Porosity: variable, 6-15% porosity Other Information: Production is from Red River Permeability: no information C Winnipegosis, Interlake, Nisku 17500 Oil/Gas Column: no information Gunton and Duperow D Average Net Pay Thickness: "A" is 6 feet; "B" is 2-6 feet Cumulative Production: 890,541 BO Figure FP-9.3. Wakea field "C" is 8-17 feet; "D" is 6-22 feet and type log. Top of Red River 10800 Other formations with shows: Mississippian Ratcliffe, Mission Canyon is datum with a contour interval Other information: Production from Red River and Interlake of 20' (after Monson, 1985).

Page 9 of 13 Fort Peck Reservation CONVENTIONAL PLAY TYPE 2 Montana Ordovician Red River Play FRACTURE ZONE Analog Fields RELATED TO BASEMENT CRETACEOUS PLAY TYPE 3 ZONE OF WEAKNESS ( * denotes fields lying within the Reservation) Ddb Devonian Nisku-Salt Collapse Play JURASSIC Benrud, East (1962) 2.9 MMBO 2 wells Dpe Benrud, NE (1964) 1.0 MMBO 1 well General Characteristics - This play is characterized by small scale non-tectonic Dw MISS. Lustre, North (1983) 179,000 BO 1 well structures. Multiple episodes of salt solution and collapse resulted in the Si Midfork (1985) 324,000 BO 5 wells development of 'turtle' structures. These structures were produced by periodic Stage 1 - Stratigraphic diagram showing pre- solution disposition of lower Paleozoic beds in Dn (multiple pay horizons) salt solution, infilling with Nisku carbonate, and final stage of salt solution, Tule Creek Field Area. Dd Palomino (1980) 2.13 MMBO 5 wells withdrawal and compaction (see Figure FP-10.1). Nisku production is 60 miles Poplar East (1952) 46 MMBO 46 wells west of the present day Prairie Salt solution edge (FP-10.1 &10.2). Dsr (multiple pay horizons) Ddb Fields are characterized by pay thickness of up to 50 feet of saccharodial, Ddb Dpe Poplar, NW (1952) 3.9 MMBO 26 wells porous dolomite (see Figures FP-10.3 & 10.4). Many of the fields have the entire Dw (multiple pay horizons) Dw Si dolomite facies equal to the pay thickness. Porosities and permeabilities are high Tule Creek (1960) 8.2 MMBO 3 wells Si Stage 4 - Stratigraphic diagram showing effects of (10 to 18% porosity, 16-30 md, occasionally as high as 100md). Numerous Tule Creek, East (1964) 2.1 MMBO 1 well Stage 2 - Stratigraphic diagram showing first stage second-stage solution and regional removal of potential exploration targets of this type may exist within the reservation area of salt solution which created local solutional sink. salts of Prairie Formation. Tule Creek, So. (1964) 900,000 BO 1 well however, field size will probably be small (250,000 BO - 1.5 MMBO). Volt (1964) 3.4 MMBO 4 wells S A S K A T C H E W A N (multiple pay horizons) Present Mm Solutional Zero Edge Prairie Salt Dn TULE CREEK Dd NISKU FIELDS TYPE LOG Dsr M O N T A THREE FORKS

N O R T H D A K FORMATION Ddb R 47 E R 48 E Dpe Inferred Dw Depositional Zero Prairie Salt 7600 Si Stage 3 - Stratigraphic diagram showing post-solution Map showing position of (1) present-day solutional NISKU infill of sink with carbonates of Souris River Formation. FORMATION edge of Prairie salt, and (2) inferred depositional Perf: 7641' - 7651' edge of Prairie Salt. IPF 450 BOPD 0 WATER Figure FP-10.1 - Stages of Nisku trap development due to salt solution features (after 3/62 Swenson,1957). OIL WATER -4980

o 110 o o DUPEROW 7700 Blackfeet 105 100 FORMATION 1000 800 1200 2000 A 1000 1800 1000 -4960 800 Ft. Belknap Ft. Peck 1600 800 T A' -4970 600 600 1400 30 400 1200 Ft. Berthold 400 -4980 N -4990 200 MONTANA -4920 -4960 Sonic -4930 200 -5000 0 -4950

Resistivity -4940 200 -5010 NORTH DAKOTA Conductivity -4960 60 40 100 400 Standing Rock -5020 INTERVAL TRANSIT TIME microseconds per foot

-5030

-5040 200 23 24 SOUTH DAKOTA EXPLANATION 0 40 40 80 RESISTIVITY Devonian or older WYOMING 80 120 rocks exposed at API Units land surface CONDUCTIVITY LATEROLOG Thickness in feet GAMMA RAY 200 of Devonian rocks Company HUMBLE OIL & REFINING CO Limit of Prairie salt of Well No. 2 J.H. BARACKER informal subsurface usage Field TULE CREEK TULE CREEK FIELD STRUCTURE MAP County ROOSEVELT State MONTANA Roosevelt County, Montana Oil field, Devonian reservoir Top of 1st Lobe Porosity - Nisku Formation Source rocks, Bakken Fm. (Dow, 1974) Figure FP-10.4. Tule Creek Field Structure Map, 10' contour interval. Figure FP-10.3. Tule Creek type log showing position of Figure FP-10.2. Thickness of Devonian rocks, limit of Prairie Salt, limit of Bakken Source rock, Fort Peck porosity development and typical initial production data. Reservation and location of regional cross-section A-A' (modified after Peterson, 1987).

Fort Peck Reservation CONVENTIONAL PLAY TYPE 3 Page 10 of 13 Montana Devonian Nisku-Salt Collapse Play PLAY TYPE 4 Pre-Prairie (Winnipegosis / Interlake) Play PLAY TYPE 6 Bakken Fairway Play General Characteristics- Regional carbonate units of lower Devonian and Silurian age are overlain by the Prairie Evaporite which acts as a seal rock. Typical reservoirs in the Winnipegosis are reefs or General Characteristics - The fractured Bakken Formation can be subdivided into three dolomitized carbonate mounds. Unconformity traps are thought to exist in the Silurian Interlake which distinct rock types. The upper and lower zones are black shale with a high organic matter can be dolomitized reefs or tidal deposits. Thickness of the Interlake Formation across the reservation area content. The middle zone is a relatively lean organic shale/siltstone. U.S.G.S. analyses of ranges from 200-300' (Figure FP-11.1). Production at Fort Peck has been confined to small scale the Bakken indicates that 11.5-12.1 weight percent of the shale is organic carbon. Evidence structures in the northeast corner of the Reservation. suggests that the Bakken has generated hundreds of million barrels of oil (some suggest The Ordovician Red River shales are thought to be the source rocks for this play and are thermally close to 1 billion) but production/migration from the interval is problematic. Production mature within the basin center. Typical traps are gentle folds with faulting, associated with regional within the Bakken must be concentrated in intervals where fractures (original or induced) structure. Stratigraphic traps (either pinch-outs or porosity variations) may exist. can remain open to fluid flow. Bakken, where it exists, is thermally mature (see Fig. FP-11.2). It forms a continuously sourced, self-sealed reservoir. Production is controlled by fractures; matrix porosity and permeability are low. Different fairways are assumed to exist. The areas with the highest 110 100 105 potential have elevated thermal maturity, proximity to subcrop, close fracture spacing and proximity to basin flexure hinge lines. Vitrinite reflectance should be greater than 0.9-1.02. A Ft. Peck 1100 A' Antelope

Ft. Berthold 900 Reservation 700 Canada 0 United States 500 0 North Dakota 300 ?

Montana 100

? 200 100

225

125 ? 250 Silurian and 225 older rocks exposed Immature 200 South Dakota Approximate Limit Of Bakken Formation "Low-Resistivity" Limey dolomite facies Bakken Shale Wyoming 0 (Modified from Sandberg, 1962) Organic-rich rocks 150 dolomite facies Mature "High" Resistivity Bakken Shale 175 have not yet generated Organic-rich rocks have generated 100 contour interval, 200' hydrocarbons - matrix hydrocarbons-matrix porosity is porosity is water Resistivity oil saturated. saturated. Control Point Figure FP-11.1. Thickness of Silurian Interlake Formation, facies, and location of regional cross-section A-A' (modified (Induction or Laterolog) after Peterson, 1987). 0 30 60 North Dakota Miles South Dakota PLAY TYPE 5

Pre-Red River Gas Play Montana

General Characteristics- Production has been established from Ordovician (Winnipeg) and Cambrian (Deadwood) sandstones within the Williston Basin. Typically these intervals contain a diagenetic Figure FP-11.2 - Areas of 'high' and 'low' electrical resistivity in Bakken shales, with subsurface isotherm contours (degrees) and overprint which has occluded most of the primary porosity; i.e. carbonate and silica secondary cement in interpreted area of source-rock maturity (after F. Meissner, 1987). pore throats. However, fracture enhanced porosity or preserved primary porosity associated with overpressured source intervals may be present. Between 600-800 feet of Cambrian and Ordovician sediments may be present across the reservation area. Potential reservoir rock is primarily a quartz-arenite sandstone with thin stringers of shale, siltstone, and limestone interbedded within the interval. These units are located within the thermally mature or over mature hydrocarbon window within the basin. Both gas and condensate are produced. Source rock for this interval is considered to be organic-rich marine shales within the Winnipeg horizon. Hydrocarbon generation probably occurred in late Cretaceous to early Tertiary time. Traps are asymmetric folds associated with basement-involved structural trends. These structures are generally highly faulted with multiple episodes of fault re-activation.

Fort Peck Reservation UNCONVENTIONAL/CONVENTIONAL PLAY TYPES Page 11 of 13 Montana (4) Pre-Prairie, (5) Pre-Red River Gas, (6) Bakken Play 112 Figure FP-12.1. 110 102 108 106 CANADA 104 PLAY TYPE 7 Paleogeographic map of 48 UNITED STATES Cretaceous Sands-Biogenic Gas (Muddy, Judith Cretaceous North America during SWEETGRASS Epeiric Seaway HILLS BEARPAW MTNS BOWDOIN Late Cretaceous time, A DOME A' River, Eagle) Greenland showing the Cretaceous POPLAR Alaska DOME NESSON ANTICLINE LITTLE ROCKY 48 seaway (after Rice and MTNS General Characteristics - Upper Cretaceous sandstones produce west of the Shurr, 1980). Fort Peck Reservation at Bowdoin Dome. Studies by Rice and Shurr (1980) CAT CREEK ANTICLINE WESTERN LIMIT CEDAR CREEK indicate that nearshore and barrier island sandstone deposits exist within the ANTICLINE 47 Cretaceous section in the reservation boundaries (Figures FP 12.1 and 12.3). CENTRAL MONTANA Shallow late Cretaceous and early Tertiary organic-rich shales may provide UPLIFT OF the source of biogenic gas; especially in the central/western portion of the PORCUPINE WILLISTON BASIN DOME ND reservation. Source quality and thickness is unknown, however, the kerogen Canada 46 SD is a mixture of algal and terrestrially derived material.

Cretaceous PRYOR Numerous gas shows have been recorded in over a dozen wells on NORTHERN LIMIT - Epeiric Seaway UPLIFT BIG HORN POWDER RIVER BASIN the Fort Peck Reservation (Table FP 12.1). It is unclear whether the shows MTNS United MT States 45 are all biogenic or a mixture of biogenic/thermogenic gases. Regional WY 0 Cretaceous BLACK HILLS structure plays an important role in providing migration conduits but also in Epeiric Seaway UPLIFT creating favorable trapping mechanisms. Presence of sealing horizons are 44 problematic and probably transient with respect to trapping/accumulating

Mexico Cuba gas. Additional exploration data needs to be acquired to address the source Figure FP-12.2. Major structural elements of the area, showing location of cross- and seal issues. section A-A' (after Rice and Shurr, 1980).

Table FP-12.1: Cretaceous Gas Shows, Fort Peck Reservation Figure FP-12.3. 180 Mi 90 Mi 150 Mi A Diagrammatic sequence A' Well Name Location Kjr Kea Knb Kgh Kmw Kmd Kd Source GLACIER NAT'L PARK of selected Cretaceous MARINE SHALE & WILLOW CREEK NONMARINE ROCKS SILTSTONE Rocks from Glacier BEST WELLS FM (PART) COASTAL SANDSTONE National Park to the west W.P. Tribal 1 8-29-49 x x x x x GL CHALK & LIMESTONE flank of the Williston Probe Tribal 1 16-31-48 x x x x x x GL CALCAREOUS SHALE Basin, Montana (after Chaske 42-32 32-30-50 x x x x x GL ST MARY RIVER FM BEARPAW Rice and Shurr, 1980). MTNS Franz 1 30-31-45 x x x x GL Tweten 1-19 19-31-44 x x x x x GL,R WEST FLANK WILLISTON BASIN Tovas 21-34 34-30-47 x x x x GL HORSETHIEF Treasure St. Farms 31-32-46 x x x GL BEARPAW SHALE SANDSTONE FOX DOME HILLS SS HELL CREEK FM. EPU WELLS FOX HILLS SS Shows 28,29-50,51 15 1 C BEARPAW SHALE EPU 10 G 30-29-51 x PT-630 EPU 5 G 29-29-51 x PT-650 JUDITH RIVER FM EPU 4 G 33-29-51 x PT-180 PIERRE SHALE OTHER WELLS CLAGGETT SHALE ARDMORE BENTONITE BED Multiple Shows Reservation 3 2 2 1 2 1 1 GL,S EAGLE SS Judith River Reservation 11 C,DST,S TWO MEDICINE FORMATION VIRGELLE SS GAMMON Multiple Shows Near Reserv. 3 4 4 4 GL TELEGRAPH SHALE CREEK FM. NIOBRARA FM CARLILE SHALE Total Shows 42 16 12 12 6 2 1 MARIAS RIVER SHALE BELLE FOURCHE SH GREENHORN FM Upper Cretaceous GL=Gas Log, R=Geologist, C=Completion Report, PT=Production IP mcfgpd MOWRY SHALE Lower Cretaceous DST=Drill Stem Test, S=Sample Log, Kjr=Judith River, Kea=Eagle, Knb=Niobrara, Kgh=Greenhorn, Kmw=Mowry, Kmd=Muddy, Kd=Dakota SKULL CREEK SHALE VAUGHN MUDDY SS MBR BLACKLEAF FM

Fort Peck Reservation UNCONVENTIONAL PLAY TYPE 7 Page 12 of 13 Montana Cretaceous Sands (Muddy, Judith River, Eagle) Ft. Peck Reservation General References Chamberlin, Virgil R., 1985, "Benrud, East Field", Montana Oil and Gas Field Zachos, Louis G., 1985, "Lustre Field"; Montana Oil and Gas Field Symposium, Symposium, Montana Geological Society, Billings, Montana, pp. 211-214. Montana Geological Society, Billings, Montana, pp. 737-738 and map Anderson, Robert C., 1995, The Oil and Gas Opportunity on Indian Lands- pocket Exploration Policies and Procedures, Bureau of Indian Affairs, Division of ______, 1985, "Benrud, Northeast Field", Montana Oil and Gas Field Energy and Mineral Resources, General Publication G-95-3, 158 p. Symposium, Montana Geological Society, Billings, Montana, pp. 215-216. Fort Peck - Map References

Beeman, William R., et al., 1996, Digital Map Data, Text and Graphical Images Diehl, L.A., 1985, Poplar, "Northwest Field", Montana Oil and Gas Field Executive Reference Map 334, 1985 edition, Extended Area, Northern Rocky in Support of the 1995 Assessment of United States Oil and Gas Resources, Symposium, Montana Geological Society, Billings, Montana, pp. 893-895. Mountains, Geomap Company. United States Geological Survey, Digital Data Series DDS-35, CD ROM. Grabb, Robert F., 1985, "Palomino Field", Montana Oil and Gas Field Executive Reference Map 321, 1983 edition, Southern Williston Basin, Geomap Charpenteir, Ronald R., et al., 1996, Tubular Data, Text, and Graphical Images Symposium, Montana Geological Society, Billings, Montana, pp. 853-855. Company. in Support of the 1995 National Assessment of United States Oil and Gas Resources, United States Geological Survey, Digital Data Series DDS-36, Hargrove, Howard R., 1985, "Tule Creek Field", Montana Oil and Gas Field Indian Land Areas, 1992, United States Department of the Interior-Bureau of CD ROM. Symposium, Montana Geological Society, Billings, Montana, pp. 1131- Indian Affairs. 1134. Gautier, Donald L., et al., 1996, 1995 National Assessment of United States Oil Clayton, Lee, et al., 1980, Geological Map of North Dakota Survey. and Gas Resources - Results, Methodology, and Supporting Data, United Monson, Lawrence M., 1995, Fort Peck Reservation Oil Summary, Part I: States Geological Survey Digital Data Series DDS-30 Release 2. Reservoirs, Production, and Reserves", Seventh Annual Williston Basin Darton, N.H., et al., 1951, Geologic Map of South Dakota, United States Symposium, Montana Geological Society, Billings, Montana, pp. 253-264. Geological Survey. ______., et al., 1995, 1995 National Assessment of United States Oil and Gas Resources, Overview of the 1995 National Assessment of Potential ______, et al., 1995, "Fort Peck Reservation Oil Summary, Part II: Ross, Clyde P., et al., 1958, Geological Map of Montana, Montana Bureau of Additions to Technically Recoverable Resources of Oil and Gas - Onshore Exploration Opportunities", Seventh Annual Williston Basin Symposium, Mines. and State Waters of the United States, United States Geological Survey Montana Geological Society, Billings, Montana, pp. 265-278. Circular 1118, 20 p. ______, et al., 1995, "Cretaceous System Stratigraphy and Shallow Gas Mallory, William Wyman, et al., 1972, Geologic Atlas of the Rocky Mountain Resources on the Fort Peck Reservation, Northeastern Montana", Seventh Region, Rocky Mountain Association of Geologists ,331 p. International Williston Basin Symposium, Montana Geological Society, Billings, Montana, pp. 163-176. Peterson, James A. and MacCary, Lawrence M., 1987, "Regional Stratigraphy and General Petroleum Geology of the U.S. Portion of the Williston Basin ______, et al., 1995, "Evaluating Mineral Resource Potential on the Fort and Adjacent Areas", Williston Basin: Anatomy of a Cratonic Oil Province, Peck Reservation Using GIS Analysis", Seventh International Williston Rocky Mountain Association of Geologists, pp. 9-43. Basin Symposium, Montana Geological Society, Billings, Montana, pp. 367-372. Rice, Dudley D. and Shurr, George W., July 1980, "Shallow, Low-Permeability Reservoirs of the Northern Great Plains - Assessment of their Natural Gas Peterson, James A, 1996, "Williston Basin Province (031)", Tabular Data, text, Resources", American Association of Petroleum Geologists Bulletin, and Graphical Images In Support of the 1995 National Assessment of Untied Volume 64/7, pp. 969-987. States Oil and Gas Resources, United States Geological Survey, Digital Data Series DDS-36, CD ROM. Willette, Donna C., et al., 1996, "Oil and Gas Atlas on Indian Lands", Indian Resources Building Partnerships, Sixth Annual Energy and Minerals Reeves, S.E., 1985, "Lisa", "Tule Creek", East Field"' Montana Oil and Gas Conference, Bureau of Indian Affairs, Division of Energy and Mineral Field Symposium, Montana Geological Society, Billings, Montana, Resources, 10 p. pp. 1135-1137

Fort Peck - Fields and Articles ______, et al., 1985, "Volt Field"; Montana Oil and Gas Field Symposium, Montana Geological Society, Billings, Montana, Ames, Vincent, 1985, "Reserve Field", Montana Oil and Gas Field Symposium, pp. 1155-1160. Montana Geological Society, Billings, Montana, pp. 955-959. Shurr, George W., 1995, "Tectonic Setting and Paleotectonic History of the Fort Anderson, Robert C., 1995, "Fort Peck Indian Reservation - The Assiniboine Peck Reservation in Northeastern Montana", Seventh International Williston and Sioux Tribes", The Oil and Gas Opportunity on Indian Lands - Basin Symposium, Montana Geological Society, Billings, Montana, Exploration Policies and Procedures, Bureau of Indian Affairs, Division of pp. 11-22 Energy and Mineral Resources, General Publication G-95-3, pp. 43-53. Swenson, Robert E., 1967, "Trap Mechanics in Nisku Formation of Northeast Brunson, Tim, 1985, "Poplar, East Field", Montana Oil and Gas Field Montana", American Association of Petroleum Geologists Bulletin, Volume Symposium, Montana Geological Society, Billings, Montana, pp. 889-891, 51/10, pp. 1948-1958. map in back pocket.

Page 13 of 13 Fort Peck Reservation REFERENCES Montana