WIND RIVER RESERVATION List of Topics

Background Reservation Overview￿ Petroleum System Overview Geologic Overview Petroleum Systems￿ Summary of play types Conventional / Unconventional Play Types Play Type 1 - Basin Margin Subthrust Play￿ Play Type 2 - Basin Margin Anticline Play￿ Play Type 3 - Deep Basin Structure Play Type 4 - Muddy Sandstone Stratigraphic Play Play Types 5,6,7 - Phosphoria Stratigraphic, Bighorn Wedge-Edge Pinchout Flathead-Lander and Equivalent Sandstone Play Play Types 8,9,10,12 - Madison Limestone, Darwin-Amsden Sandstone Triassic and Jurassic Stratigraphic, Cody and Frontier Play Type 11 - Shallow Tertiary/Upper Cretaceous Stratigraphic Play￿ Play Type 13 - Basin-Center Gas Play References OVERVIEW allow a credit to the operator/producer for amounts paid to Wyoming and has issued credits of over $12,000.000 WIND RIVER RESERVATION ￿ Due to the declining economy and declining production of the aging fields, The Shoshone and Arapahoe Tribes revenues to the JBC from taxation has been on a dramatic decline. In addition, due to the increased population of its non-Indian and corporate citizens, the JBC TRIBAL HEADQUARTERS:￿ Fort Washakie, Wyoming was and is in dire need of increased revenues in order to provide essential GEOLOGIC SETTING:￿ Wind River Basin government services, medical services, basic transportation, housing, police protection, fire protection, and solid waste disposal. The demand for these basic infrastructure services far exceeds the severance tax revenues. General Setting ￿ However, the JBC realizes that it cannot continue to raise its tax rates in order ￿ Currently, the Wind River Indian Reservation contains about 3500 square to meet this demand. Therefore, it has been lobbying the Congress to effect some miles of land. The reservation stretches from the northern part of the Owl Creek type of change in federal law that will aid Indian Tribes in their efforts to induce mountains to Sand Draw in the South. To the east it begins just west of Shoshone economic activity on Indian Reservations. and extends westward to the town of Dubois. There are approximately 2,500 ￿ The JBC has been lobbying for investment tax credits, employment tax Shoshone and approximately 5,000 Arapaho on the reservation. credits and have even lobbied for apportionment of state and tribal taxes. However, in the last three years, the JBC has had no success with this campaign. Government Other energy producing tribes and industry have also lobbied for these ￿ The Wind River Reservation is governed as follows: Each tribe has its own incentives, but with no success. 191 20 General Council that meets about three times a year. A General Council is 16 ￿ In addition, the Tribes have joined one taxpayer on the Reservation in a Park composed of each member of the tribe 18 years and older and is similar to a town Teton lawsuit against the state of Wyoming. The agreement between the Tribes and this meeting. The General Council of each tribe has delegated certain powers to the Worland taxpayer comes under the 1982 Indian Mineral Development Act. Other Business Council, but retains most major decision making authority. companies that would like to do oil and gas business with the Tribes should ￿ The Arapaho Business Council and the Shoshone Business Council each have Moran seriously consider entering into these type of agreements, if they want to avoid Washakie six members. Each tribe elects six members for a two year term. Each Business Hot Springs dual taxation. Council elects a chairman. Together, these twelve members comprise the Joint ￿ Finally, the Tribes have been negotiating with Wyoming for several years Business Council (JBC) of the Shoshone and Arapaho Tribes. The Joint Thermopolis concerning the dual taxation problem. However, after the Cotton Petroleum 26 Business Council is directly responsible for the day to day activities on jointly decision, Wyoming's position on this problem appears to be stronger. But it is Jackson owned resources and joint programs of the tribes. WIND RIVER 20 important to differentiate the facts of that case with the facts of the case Shoshone mentioned above. The most important difference being the type of agreement Wind River Indian Reservation Tax Structure 83 entered into between the tribes and the company. The Tribes are pushing for a 189 ￿ On December 12, 1978, the Joint Business Council (JBC) of the Shoshone solution of the dual taxation problem on the Wind River Indian Reservation, 26 20 and Arapaho Tribes enacted Ordinance Number 39, effective April 2, 1979. The which would serve as a model for all of Indian country. Riverton Ordinance imposed a one-half of one percent (0.5%) Privilege of Doing Business 789 Tax on the market value of gas produced, saved and/or sold or transported from Sublette Fremont Contacts Boulder Lander the field where produced within the exterior boundaries of the reservation. ￿ The Joint Business Council feels it is in the best interest of their people to Subsequently, the JBC amended Ordinance Number 39 on March 10,1982 and fully develop their oil and gas resources in an efficient, economic, and 287 increased the tax rate from one-half of one percent (0.5%) to four percent (4.0%). 191 environmentally sound method. The Joint Business Council will accept 189 ￿ None of the oil and gas companies operating on the reservation at that time 28 proposals at your earliest convenience. The Joint Business Council along with paid the tax. Several of the major oil and gas producers filed suit against the staff of the Wind River Tax Commission, the Shoshone Oil and Gas Commission Tribes challenging their authority to impose taxes on their production. On May 7, and the attorneys will evaluate all proposals within thirty days of submittal. The 1982 the Federal District Court in Cheyenne ordered the companies to start Joint Business Council will then act on the recommendation of the staff and paying the tax into an escrow account under its control. Although, the JBC attorneys within thirty days of the committee's action. enacted the Ordinance back in 1978, no revenues flowed to the Tribes until June ￿ For additional information, please mail your request and/or proposal to the of 1986. ￿ On May 6, 1986, the United States District Court dismissed the suit against following: the Tribes, due to a previous United States Supreme Court decision which allowed Indian Tribal Governments the authority to tax within their boundaries. Since, that time the JBC and the Wind River Tax Commission have collected Joint Business Council millions of dollars to support and finance the services it provides to its citizens. Shoshone and Arapaho Tribes ￿ On June 19, 1987, the JBC, again amended Ordinance Number 39. The c/o Wind River Tax Commission amended Ordinance created the Wind River Tax Commission. In addition, the P.O. Box 830 JBC increased the tax rate from four percent to four percent plus amounts paid to Wyoming and its subdivisions. The state of Wyoming imposes a six percent Fort Washakie, Wyoming 82514 (6.0%) severance, a one-half of one percent conservation and approximately seven percent in ad valorem taxes. Thus, the total tribal tax would be closer to seventeen percent (17.0%). However, the JBC realized by increasing the tax rate, it would drive the operators off the reservation. Therefore, the JBC decided to

Wind River Reservation RESERVATION OVERVIEW Page 1 of 18 Wyoming Structure contours on top of Lower WIND RIVER BASIN AREA Cretaceous Dakota Sandstone or 5000 equivalent on margins of basin

Projected structural contour (approx. - Wind River Basin - Petroleum System Overview 10,000') on the top of the Dakota Wind River Reservation Washakie Sandstone Owl ￿ The Wind River Basin is a northwest-southeast trending Hot Springs County Anticline or syncline - showing direction Stratigraphic Column of plunge County asymmetrical intermontane basin of the Rocky Mountain Foreland, Creek Thrust fault - teeth on upside Wind River Reservation Area 0 located in central Wyoming. Province boundaries are defined by Mountains Normal or reverse fault fault-bounded Laramide uplifts that surround it. These include the 0 Natrona Surface fault - unknown structural extent County Precambrian outcrop Owl Creek Mountains to the north, Wind River Mountains to the Paleogene & Neogene Undifferentiated -5000' 5000' Tertiary volcanics outcrop west, Casper arch to the east, and the Sweetwater Uplift to the south. 5000' Wind River Fm Oil Field Eocene The Wind River Basin Province is about 200 mi. long and 100 mi. Indian Meadows Fm Gas Field wide, encompassing an area of about 11,700 sq. mi. Actual basinal

Oil and Gas Field Cenozoic Fort Union Fm 0 Casper Paleocene area not capped by eroded Precambrian and/or Paleozoic rock is TERTIARY S 5000' Figure WR 2.1 - approximately 7,500 sq. mi. The Wind River Reservation comprises Lance Fm

-5000' Tectonic features, almost half of this basinal area, 3,500 sq. mi. All of the major Meeteese Fm Arch structure and field -5000' petroleum systems and play types have been encountered in the Mesaverde Ss distribution map (after 5000' Wind Upper 0 reservation area. Approximately 0.55 BBO , 35 MMBNGL, and Cody Sh 5000' Johnson & Rice, 1993.) Fremont 0 2.9 TCFG are known to have been produced from the entire basin County -5000' Frontier Fm 5000' -10,000 since 1884. 0 5000' Mowry Sh River ￿ A nearly complete stratigraphic section, Cambrian through S Sweetwater Tertiary in age fill the sub-basins located within the reservation area CRETACEOUS Muddy Ss 0 N 5000' of the Wind River Basin. Sevier-aged and Cretaceous epicontinental Thermopolis Sh

Lower Lower S Uplift seaway basins have been complexly folded, thrusted, and faulted Range

Mesozoic Cloverly Fm Sublette County 5000' during the Laramide orogenic event (initiated latest Cret.-earliest Morrison Fm Paleocene). Basement involved and detached structural features create intricate and complicated stratigraphic correlations throughout JURASSIC Sundance Fm Map Fremont County Carbon the Wind River Basin. Early paleozoic platform carbonates and Gypsum Springs Fm Area County 0 30 mi fringing patch reefs of a mainly carbonate province become Nugget Ss Wyoming Sweetwater County Contour interval = 5000' siliciclastic-dominated by latest Paleozoic time. Sandstone reservoirs 0 40 km TRIASSIC Chugwater Gp of the Permian Phosphoria Formation and Pennsylvanian Tensleep Dinwoody Fm T 9 produce the bulk of the petroleum within the reservation area. 2000' PERMIAN Wind River Reservation N Locally, many of the other Cretaceous sandstone reservoirs produce Phosphoria Fm S T Surface Features and 3000' 8 Tensleep Ss N significant quantities of oil and gas. Black shales of the Phosphoria PENNSYLVANIAN Oil & Gas Fields and Mowry formations are considered the source of the petroleum for Amsden Fm 5000' 5000' 4000' T 7 much of the Wind River basin reservoirs. Deeply buried Cretaceous MISSISSIPPIAN S.L. N Madison Ls Circle Ridge and Tertiary coals are probably the source of significant amounts of 5000' Maverick Springs T S.L. S.L. Bighorn Dol 6 ORDOVICIAN

N thermogenic methane (gas) found in Cretaceous/Tertiary reservoirs. Paleozoic Rolff Lake Maverick Springs SE Sheldon -5000' S.L. -10,000' Gallatin Ls Dome NW -7000' Little Dome T Sheldon W. Sheldon 5 N CAMBRIAN Gros Ventre Fm Legend (abnd) Dome -5000' Pavillion Structure contours to the north and east of NW (abnd) yellow line are drawn on top of Paleocene S.L. -5000' Flathead Ss Mexican Muddy Ridge T Fort Union Formation--contours to 4 the south and west are drawn on top Draw (abnd) 5000' N of the Permian Park City Formation -10,000' Steamboat Sand Mesa PRECAMBRIAN Undifferentiated Major thrust faults Undiscovered Resource Butte -5000' Discovered Resource 5000' Pavillion T Contour interval-every 5000',2000' or Pilot Butte Source horizon 3 S 1000' where appropriate Boysen 500 N Oil field Tertiary volcanic 500 3.0 Production from reservoirs outcrop Pilot S. T 3.0 Oil Gas Gas field Undifferentiated -5000' Ocean Lake 2 400 in approx. proportions precambrian Winkleman S.L. N 400 Oil and gas field and paleozoic outcrop Sage Creek N. T Wind River Basin 300 2.0 Figure WR 2.3 - Stratigraphic column for Wind River Indian 2.0 1 300 Wind River Basin Butte Sage Creek S.L. -10,000' N Oil TCF Basin (Willette, D., 1996). 0 5 10 15 Miles Anticline (abnd) MMBO

TCF 200 Riverton E. 200 T MMBO Gas 5 10 15 20 Kilometers 1.0 1.0 North 1 Gas Plunkett (abnd) S 100 100 Sharp Nose(abnd) Riverton Alkali Estimates from U.S.G.S. Estimates from U.S.G.S. Dome Butte Oil 1995 T2S 1995 0 Lander R3E R4E R5E R6E 0 0 0 R1E R5W R4W R3W R2W R1W R2E Figure WR-2.4. These graphs depict the estimates for discovered and undiscovered hydrocarbons Figure WR 2.2 - Reservation area and distribution of oil and gas fields. The reservation area contains many of the large within the Wind River Basin. The bulk of new discoveries should be gas with over 100 MMBO added surface structural features drilled early in the exploration history of the Wind River Basin; Sage Creek Anticline (1886) to production as well. Historic ratios of oil versus gas discoveries will not apply in the future as and Lander fields(1912) for example. Major structural features both shallow and deep account for significant production exploration efforts will most likely target for new gas reserves (Willette & USGS, 1996). from the reservation area. Winkleman Dome and Steamboat Butte have each produced over 90 MMBO. Circle Ridge has produced over 34MMBO. Pilot Butte, Maverick Springs, and Lander have each produced over 10 MMBO. Gas production from Riverton Dome and Pavillion fields exceed 175 BCFG per field. Deep basin gas and subthrust plays provide the bulk of the future petroleum potential. (after Johnson and Rice, 1993).

INTRODUCTION Wind River Reservation Page 2 of 18 Wyoming Petroleum System Overview Regional Geology ￿ The Wind River Basin occupies the geographic center of Wyoming and is surrounded by some of 3000 120-100 mya 140-120 mya Wyoming's highest mountains. The Wind River Mountains (13,500+ feet in elevation) form the 2000 western boundary of the basin against which several major southwest verging thrust systems abut. The northern margin of the basin is constrained by the Owl Creek and southern Big Horn Mountains, while Wyoming Wyoming the southern basin margin is marked by the Granite Mountains. The eastern edge of the basin is Sevier delineated by the more subtle topography of the Casper arch which separates the Wind River basin Wind River Wind River Reservation Reservation from the Powder River basin. The basin is 180 miles long, northwest to southeast and is 75 miles wide north to south. The reservation area comprises most of the northwestern and central portions of the basin. The predominant pattern of deposition for both the Paleozoic and Mesozoic intervals consist of Orogenic 1000 500 complexly interbedded sandstone and shales. Only the lower Paleozoic section contains carbonate and

1000 evaporite deposits. Belt 3000

500 Isopach of Paleozoic and early Mesozoic Geologic History Isopach of Upper Lower Cretaceous ￿ During Paleozoic and early Mesozoic time all of central Wyoming was part of the stable shelf Lower Cretaceous Deposition lying east of the Cordilleran orogenic belt. Deposition upon the shelf occurred primarily in shallow Deposition seas. Because of the broad shelfal, area widespread facies changes and unconformities resulted from relatively minor sea level fluctuations. ￿ Combined thickness of Cambrian-aged deposits range from 1025' in the western edge of the basin A B to approximately 775' in the east. The Flathead Sandstone and the Gros Ventre Formations consist of predominantly clastic deposits while the Upper Cambrian Gallatin Limestone provides the first evidence of carbonate depositional conditions within the shallow, shelfal environment. ￿ Ordovician-aged sediments of the Wind River Reservation are represented only by the Bighorn Dolomite. Estimates in thickness range from 125-300 feet and the dolomite thins to the east and southeast and is absent in the southeast corner of the reservation due to an erosional unconformity.

500 1000 Devonian rocks are thin to absent across the reservation area. The Madison Limestone comprises most 100 - 80 mya 80 - 64 mya of the Mississippian-aged sediments within the reservation. It ranges between 500-700 feet in

5000 2000 thickness with the upper portion containing karst features. 1000 Wyoming 2000 4000 10000 ￿ During Pennsylvanian and Permian time, marine deposition became progressively more Wyoming terrestrially influenced. The Amsden Formation consists of dolomite, shale, sandstone, and limestone 5000 Wind River Reservation ranging between 250-350 feet thick. The Tensleep Sandstone is a known reservoir interval containing Wind River massive to cross-bedded shelf and eolian sandstone deposits between 200-400 feet thick. By Permian Reservation 6000 12000 time, the reservation area alternated between terrestrial shoreline and restricted carbonate depositional 10000 O environments. The Phosphoria Formation contains an organic-rich source interval, dolomite, shale, 8000 r i 1000 g 500 and limestone deposits between 200-300 feet thick. i n a Lower Triassic deposits contain the Dinwoody Formation (50-150 feet thick), dominantly l

T terrestrial Chugwater Group deposits (800-1000') containing typical 'red bed' continental sediments, h

i c k and the Nugget Sandstone. The upper Triassic/lower Jurassic Nugget Formation is a known reservoir n e interval consisting of large-scale, cross-bedded eolian deposits. The formation is as thick as 300 feet, s s thins to the northeast, and is absent in the northern part of the reservation area. Jurassic deposition U n Isopach of k reflects both nearshore marine and fluvial conditions in the area. The Gypsum Spring and Sundance Late Upper Cretaceous no wn Formations contain oolitic limestone, glauconitic sandstone, gypsum and anhydrite ranging between Isopach of Deposition 250-350 feet thick. The Morrison Formation consists of fluvial sandstone, siltstones, and shales and Early Upper Cretaceous D Deposition contains well known dinosaur bone-beds. C Eroded or non-depositional edge along uplift of Colorado Plateau Cretaceous Geologic History ￿ Lower Cretaceous sediments reflect the first pulse of foreland basin development in the reservation area. Effects from the Sevier orogenic event located to the west are mainly restricted to relatively thin, Figure WR 3.1 - Generalized patterns of deposition in the Rocky Mountain area during Cretaceous time. A - Mid Atlantic spreading caused uplift, thrusting, fine-grained shale deposition in this area (Figure 3.1). The Cloverly Formation ranges between 250- and folding in the Sevier orogenic belt, synorogenic sediments were thick adjacent to the Sevier uplift and very thin elsewhere. B - Continued westward plate 450 feet thick and consists of 'weathered' thin sandstone deposits and paleosols representing coastal movement is reflected in uplifts on the western plate margin, thick deposits adjacent to the overthrust belt, and thin deposits over a wide area of the foreland. plain deposition. The Thermopolis and Mowry Shale Formations represent the initiation of clastic, C - Early uppermost Cretaceous deposition is thickest adjacent to the overthrust belt; a thicker section of marine sediments may reflect a general downwarping of the foreland area. D - During latest Cretaceous and early Paleocene, the spreading rate between North America and Eurasia was greatly marine epeiric sea conditions. increased. Early Laramide buckling of the basement in the foreland began to occur, and foreland uplifts formed north-south parallel to the overthrust belt (after Gries, R. 1983).

Wind River Reservation GEOLOGY OVERVIEW Page 3 of 18 Wyoming Regional Geologic History Figure WR-4.1 - Depositional Structural Evolution of Wind River Basin Owl Creek patterns of Eocene and Uplift ￿ Complex Laramide orogenic events produced a structural fabric in the Wind ￿ Early Laramide (latest Cretaceous) erosion was mostly from north-south Big Horns Paleocene time slices in the Wind River Basin. A. - Fine River area that produced polyphase structural re-orientations of major elements. trending arches and ranges (Gries, R.,1983). Eroded material included grained (non-synorogenic) However, studies of all the major Laramide Rocky Mountain basins and uplifts previously deposited Mesozoic shale, limestone, dolomite, and sandstone. As Paleocene sediments were Wind River Mountains Casper Arch show similar patterns of development. The Laramide orogenic event was uplift continued in early Paleocene, Paleozoic rock fragments became thickest at the south end of triggered by the opening of the mid-atlantic ridge and movement of the North incorporated in fluvial/alluvial sedimentation. Thick sections of lower - middle the Big Horn Mountains and 1000 in a deep trough on the north American craton along a westward directed line of motion during latest Eocene coarse, boulder conglomerates adjacent to the east-west trending ranges side of the Wind River Basin. Cretaceous time. The ridge-opening accelerated in Paleocene/Eocene time and are evidence of major uplift during the late phase of the Laramide orogeny (Fig. B. - Eocene deposition movement of the craton became directed southwestward. WR-4.1). reflected the denudation of ￿ Most structural analyses indicate that little or no vertical movement occurred ￿ Most foreland basins have thicker sections of Eocene syn-orogenic Granite 2500 the Owl Creek and other on east-west trending structures in latest Cretaceous/Paleocene time. However, sedimentary rocks than Paleocene and uppermost Cretaceous, an indication Mountains surrounding uplifts with A. 1000 substantial activity on northwest-southeast trending structures is likely and coarse-grained conglomerate perhaps of greater tectonism at the end of the Laramide orogeny than during the Paleocene Deposition and clasts of Paleozoic and produced westward verging, linear thrust sheets (Figure WR-4.2). It is possible earlier phases (Gries, R., 1983). Wind River Basin Precambrian rocks (after that east-west trending strike-slip faults also developed along zones of basement Gries, R., 1983). weakness. ￿ Development of east-west trending thrust sheets occurred during maximum compression (southward directed) in Eocene time. Detailed surface mapping has Owl Creek Uplift shown Eocene east-west trending thrusts and folds truncate or are superimposed Big Horns on earlier Laramide north- and northwest-trending thrusts and folds (Figure WR- 1000 4.2).

7000 Casper Arch Wind River Mountains 5000

1000 Wind River Reservation 5000 500

500 3000 B. Granite Mountains 4000 Eocene Deposition Owl Creek Mountains Legend Wind River Basin 5000 5000 Cretaceous Geologic History (Continued) Structure contours are 5000 5000 level drawn on top of the Permian ￿ As the foreland area developed and the basin began to downwarp due to crustal loading, thick piles of sediment began to -3000 sea Owl Creek Park City Formation except accumulate in front of the thrust sheets (Figure WR-3.1). The early Late Cretaceous Frontier Formation, an important oil/gas Mountains -10,000 where noted. Datum is mean producing formation, ranges in thickness between 600-1000 feet. As downwarping continued, the clastic- marine Cody Shale sea level -2500 was deposited. Accumulation ranges between 2500-5000 feet in thickness. -5000 Precambrian rock

￿ Terrestrial conditions were re-established in the reservation area by the time the Mesaverde Formation was deposited. sea level sea sea

Containing fluvial and shoreline sandstones, coal, and carbonaceous shale, the formation ranges between 1000-2000 feet in -7000 Paleozoic and older rocks -5000 -6000

thickness but is absent in the southwest part of the reservation due to later uplift and erosion. The overlying Meeteetse level Tertiary volcanics Formation contains depositional environments similar to the Mesaverde, but the interbedded coal horizons are much thicker. -5000 Plant remains and dinosaur bones have been found in this formation and it can be up to 1400 feet in thickness. Structural low ￿ As the basement buckled and uplifted during latest Cretaceous time, denudation of these highlands started to occur. The Lance Formation contains the first evidence of clasts from Paleozoic and Cambrian rocks deposited in lenticular Thrust fault conglomeratic horizons. While the thickness of the interval is highly variable, it can range up to 1200 feet in thickness. -10,000 -2500 Contour interval - Wind River 2000 1000' or 500' Cenozoic Geologic History Mountains sea level Contours east of this

￿ On the margins of the Wind River Basin the Paleocene Fort Union Formation unconformably overlies the Late Cretaceous sea level 5000 line are drawn on the top Lance Formation but in the northern and central troughs, fluvial and alluvial fan deposition continued (Figure WR 4.1). sea level lower member of Paleocene -5000 Earliest Eocene deposits of the Indian Meadows Formation contain abundant alluvial fan and channel sandstones and 4000 Fort Union Formation conglomerates. Mesozoic and Paleozoic rock clasts are common and landslide/slide block masses from these thrust sheets -9000 are present as well. By the time of the Wind River Formation deposition, Precambrian rock fragments are abundant and -10,000 reflect exposure of the igneous/metamorphic cores of the uplifts (Figure WR 4.1). The thickness of the Wind River

-2000 Formation ranges from a few feet at the basin margin, to over 6000 feet in the northern part of the reservation area. sea level Oligocene and younger sediments consist of a thin veneer of volcanic tuffs, volcanic breccia and sandstone deposits. Quaternary glacial till and outwash gravel are present in the southwestern part of the reservation.

Figure WR-4.2 - Structure map of Wind River Reservation area (after Keefer, W., 1993).

Wind River Reservation GEOLOGY OVERVIEW Page 4 of 18 Wyoming Geologic History 104 102 116 114 112 110 108 106 Lithofacies of 112 110 108 106 Phosphoria and equivalents the Meade Peak has been calculated to be 2.4%, with some beds containing as 0 100 200 Miles much as 30% organic carbon by weight. Average TOC from the Retort 48 Carbonaceous Mudstone Interbedded Carbonaceous 100 200 300 Kilometers member ranges from 4.2-4.9%, maximum values are about 10 weight percent Mudstone/Sandstone 5k Inferred Mesozoic Arrows indicate total organic carbon. Sandstone 4k thickness contours probable migration paths during late ￿ Hydrocarbon generation resulted from the effects of deep burial in Carbonate rock 46 2k 3k Thickness of Mesozoic Cretaceous westernmost Wyoming and adjacent areas (see Fig. WR-5.2). Fluids were 46 ND Red Mudstone section (in km) - probable maximum depth of burial SD 2k generated during passage of the source rocks through the oil/condensate Halite Montana window corresponding to burial depths between 2.2 - 4.5 km. Relatively 2.5k Gypsum Wyoming unimpeded migration pathways (both lateral and vertical) occurred during 3.5k Terrestrial land area 3k Late Cretaceous time just prior to the Laramide orogeny (Fig. WR-5.2). 44 44 ￿ The lower Cretaceous Mowry shales and their equivalents are major 4k source rocks in the northern Rocky Mountain - Great Plains region. They are

5k 3k one of the major sources of hydrocarbon in the Jurassic Nugget Sandstone of NB 6k southwestern Wyoming, lower Cretaceous Muddy Sandstone, and other WY 7k 2.5k 3.5k ID 8k 3k Cretaceous sandstone reservoirs. 42 9k 4k ￿ In the reservation area, the Mowry shale may range between 500 - 600 feet Idaho 4k NV UT 42 in thickness. A significant percentage of the interval includes non-source Utah 5k lithofacies such as oxic, bioturbated mudstone, sandstone and siltstone. CO 2.5k Typically, only the basal Mowry can be considered a source facies due to the Edge of carbonaceous 40 shale beds Colorado presence of anoxic, laminated mudstone. 3.5k ￿ The Mowry shales contain a mixture of predominantly type II and type III 3k o 100 200 300 Miles 40 organic matter (see Fig. WR-5.4). These organic matter types represent a 2.5k mixing of terrestrial and marine organic matter. Organic matter suites with 100 200 300 400 Kilometers this composition are typical of shallow, epicontinental seas. In general, the Figure WR-5.2 - Inferred maximum depth of burial of Phosphoria Mowry section within the reservation area contains a higher percentage of Figure WR-5.1 - Lithofacies of Phosphoria (Meade Peak Mbr) and equivalent rocks in Wyoming and adjacent areas. Formation based on thickness of Mesozoic section. Solid lines indicate terrestrially derived organic matter (more gas prone) than the shales deposited Note position of reservation relative to carbonaceous mudstone and organic-rich carbonate horizon (after Maughan, thickness of Mesozoic in kilometers, dashed lines are inferred. Arrows 1984). indicate probable migration paths during late Cretaceous time. Barbed within the axial portion of the Mowry seaway. lines are leading edge of Cordilleran overthrust belt (Maughan, 1984). ￿ Areas of anomalously low TOC values in the Mowry coincide with the Petroleum Systems Overview deeper parts of Laramide structural basins which developed after the deposition of these shales. Regional variations in the TOC content may reflect in part a reduction of the TOC by thermal maturation or abrupt ￿ In the Wind River Basin area, there are three and possibly four 3.5 4.0 2.5 3.0 variations in the precursor organic facies (see Fig. WR-5.3). source rock petroleum systems that have generated or are generating Blackleaf 1.0 1.5 2.0 Formation hydrocarbons. The reservation area is ideally situated to explore at 2.5 least three of these systems. Thrusting during the Laramide orogenic 2.0 event has obscured evidence regarding migration pathways, lithofacies 1.5 1.5 relationships, and even a clear determination of geothermal gradient in 2.5 SD 2.0 some areas. However, some generalizations can be made. MT 1000 Type I (Alginite) Figure WR-5.4 - Plot of ￿ A major source rock interval in the Wind River Basin is the WY Sandstone Mowry Shale whole rock HI vs. OI for 1.5 Skull Creek Shale Permian Phosphoria Formation which contains two organic-rich shale Mowry and Skull Creek Increasing Maturation 1.5 800 members called the Meade Peak and Retort intervals. These rocks Muddy Shale samples. Samples contain a were formed at the periphery of a foreland basin between the Paleozoic Coastal Plain 1.5 2.5 NB Sediments 2.0 mixture of dominantly

continental margin and the North American cratonic shelf (see Fig. ID 1.5 Newcastle Newcastle Fluvial Sandstone 2.0 Type II (Exinite) type II and type III WR-5.1). Restricted circulation patterns, increased biologic activity UT 600 kerogen. Oil and a Marine Sandstone 1.5 due to zones of upwelling, and resultant anoxia contributed to the strongly gas prone Batholiths 2.5 2.0 CO preservation of algal organic matter. source rock would be Land, sediment 1.5 400 ￿ Petroleum generation from the Phosphoria Formation ranges source Type III (Vitrinite/Inertinite) the result (after Burtner 6 between 24.6 - 30.7x10 metric tons according to various authors. Contour interval = & Warner, 1984). Reservoirs such as the Tensleep, Chugwater Group, and Nugget 0.5 Wt. % TOC J Sandstone 0 50 100 150 200 Sandstone contain oils which have been typed back to the Phosphoria. 200 The bulk of the oil seems to have been generated from the Miles carbonaceous mudstone strata (see Fig. WR-5.1). Figure WR-5.3 - Regional distribution of total organic carbon (TOC) in the Mowry Shale. Hydrocarbon Index (mg HC/g Corg.) Anomalously low TOC values may coincide with lithofacies variation or position with the deeper 0 ￿ Both organic-rich members of the Phosphoria occur within the portions of Laramide structural basins where significant generation/expulsion has occurred (from 50 100 150 200 250 reservation boundaries (Retort and Meade Peak). The average TOC of Burtner & Warner, 1984). Oxygen Index (mg CO2/g Corg.)

Wind River Reservation GEOLOGY OVERVIEW Page 5 of 18 Wyoming Petroleum Systems Canada U.S.A. Northwest 3) The Uppermost Cretaceous/Lower Tertiary section of the reservation Montana Trough area contain several potential source horizons; either organic-rich shales or Stratigraphic Unit (Ma) Ages

thin-bedded coals. Oil and gas produced from the Fort Union reservoirs, as Series System Williston basin or event (in feet) Thickness Bull well as oil shows in the Wind River Formation were probably generated from mid-Mio. 15 - 0 Mountain basin these intervals. In addition, Lance Formation shows and reservoired to present uplift and erosion -3,380 hydrocarbons may also be source from these zones. ￿ Figure WR-6.1 depicts the distribution of basins in which thermogenic gas Split Rock 900 24 - 15 has been generated from Tertiary or Upper Cretaceous coals, generally under Formation Crazy Miocene Mountain deep burial conditions. These coals contain typical type lll gas-generating basin Powder East limit of Laramide kerogen. These coals could charge conventional sandstone reservoirs as well White River Bighorn River structural disturbance as uncoventional 'tight' sandstones (basin-center accumulations). In addition, 500 36 - 24 basin basin Formation Western limit the coals may also provide a viable exploration target. Oligocene of Rocky Mountain Wind River ￿ Humic coals are capable of both generating and storing significant amounts Post lower Eocene Thrust and Fold Basin 1,980 of dry methane gas. Methane generation commences within the high voliatile rocks-undivided Belt 55 - 38 bituminous A coal rank, where volatile matter content is 37.8% and vitrinite Wind River and Indian Tertiary Meadows Formations reflectance is 0.73% (Meissner, 1984). Lowland areas adjacent to the Eocene 4,625 Greater undifferentiated Green River Cretaceous Seaway provided environments conducive to the formation of basin lagoonal swamps, shoreline paralic swamps, channel-overbank swamps, and Shotgun 2,175 59 - 55 Member Denver restricted lacustrine swamps. Later Laramide orogenic activity has eroded Piceance basin some of these horizons while preserving others under thick volumes of Waltman Uinta basin basin Tertiary sediment (Figure WR-6.2). Shale 840 60 - 59 ￿ In addition to coaly intervals, at least one shale horizon in the Tertiary Member Paleocene section may have the organic-richness to generate hydrocarbons (Figure WR- Lower 1,350 66 - 60 member 6.2). In the reservation area, the Waltman Shale has been modeled using Fort Union Formation Paradox Regional eastward Figure WR-6.2 - Stratigraphic column of Tertiary stratigraphy in the basin known well data and vitrinite measurements. Approximate location of this erosion limit of Upper well is located in Figure WR-6.1. reservation area of the Wind River Basin. Position of potential Cretaceous Coals source interval is depicted in brown (after Nuccio, V., 1994).

Time (Ma) San Juan basin 60 50 40 30 20 10 0 0 0 Major Laramide uplifts Raton Major Laramide basins basin Interpreted Maturity Line based on 2000 Laramide basins where 2000 100 (F) measured Ro data Cretaceous-Lower Tertiary Eocene coals have generated gas Approximate position of well + used in Tertiary section burial 4000 Modeled Maturity history model 4000 + Bottom Eocene Line + Figure WR-6.1 - Generalized map showing the distribution of major Laramide structural basins and uplifts in the constant heat + Rocky Mountain region. Eastward limit of Uppermost Cretaceous coal deposition is shown along with those basins 150 (F) flow of + Fort Union 6000 45 mWm-2 + which have reached sufficient maturity to generate gas from these coal deposits (after Meissner, F., 1984). Shotgun Member + 6000 Top Waltman Shale

￿ The major Tertiary oil source rock in the Wind River Basin is the Waltman Shale Waltman Shale ++ Depth (feet) 8000 + Member +++ member of the Fort Union Formation. The Waltman Shale contains a mixture of both + Depth (feet) 200 (F) Bottom Tertiary 8000 Lower + types II and III kerogen, with total organic carbon content values as high as 7.0 wt%. Oil Window Member Mean Ro values for samples taken from the modeled well range from .61-.9% (Figure 10000

WR-6.4). In general, oil generation is thought to begin around the .60 Ro value. 10000 ￿ Using a constant heat flow value that matched measured Ro values, a burial and 12000 temperature history of the stratigraphic interval was modeled (Figure WR-6.3). The 250 (F) maturity level for the Waltman Shale ranged between .70-.90% Ro corresponding to 12000 burial depths between 7000-10,000'. Maximum burial temperatures reached 250 degrees Farh. at about 15 Ma before present. Based on this information, the Tertiary Waltman .5 .6.7 .8 1.0 Maturity (%Ro) Shale has reached the proper maturity level to have generated hydrocarbons near the 14000 basin center. In addition, for the interval that was buried to around 11,000' may have Figure WR 6.3 - Burial history diagram depicting oil generation window relative to position of the Figure WR-6.4 - Measured and modeled Ro data from reached the critical threshold to initiate gas generation. Waltman Shale. Diagram illustrates the probable generation of hydrocarbons from this zone under well located on Figure WR 6.1. Data was input into ￿ This potential source interval may charge subthrust plays, basin-center plays, as well basin center burial conditions. Position of well from which this data was modeled is located on Figure burial history model to generate range of oil generation as conventional fold/thrust structural traps. WR-6.1 (after Nuccio, V., 1994). from the Waltman Shale (from Nuccio, V., 1994).

Wind River Reservation GEOLOGY OVERVIEW Page 6 of 18 Wyoming Petroleum Systems (continued) WIND RIVER BASIN SCHEMATIC ILLUSTRATION OF POTENTIAL HYDROCARBON TRAPPING MECHANISMS AND PLAY TYPES

Basin margin anticline play Basement involved Shallow Tertiary-Upper Cretaceous Play Types - Wind River Basin ex. Circle Ridge, Steamboat Stratigraphic and Combination traps Butte, Lander, Sage Creek ex. Muddy Ridge, Sand Mesa 1. Basin Margin Subthrust 2. Basin Margin Anticline 3. Deep Basin Structure 4. Muddy Sandstone Stratigraphic Muddy Sandstone stratigraphic play ex. Grieve, Sun Ranch and Wild 5. Phosphoria Stratigraphic Horse Butte fields 6. Bighorn wedge-edge pinch-out Basin margin subthrust play 7. Flathead-Lander and equivalent ex. Tepee Flats, deeper pool sandstone stratigraphic discovery Cave Gulch Basin margin anticline play 8. Madison Limestone Deep basin structure Detached structures stratigraphic ex. Madden, Pavillion, ex. Windrock ranch and Riverton Dome Winkleman fields 9. Darwin-Amsden sandstone stratigraphic 10. Triassic and Jurassic stratigraphic 11. Shallow Tertiary-Upper Cretaceous stratigraphic 12. Cody and Frontier stratigraphic 13. Basin-Center gas unconventional/hypothetical conventional Basin-center gas play Hypothetical

Other hypothetical plays detailed in subsequent sections

Figure WR 7.1 - Schematic illustration of play types showing distribution of hydrocarbons (modified from Willis & Groshong, 1993)

Reservation: Wind River Total Production ( by province-1996) Wind River Basin Undiscovered resources and numbers of fields are Geologic Province: Central Wind River Oil: 550 MMBO for Province-wide plays. No attempt has been made Province Area: Wind River Basin (11,700 sq. miles) Gas: 2.8 TCFG to estimate number of undiscovered fields within the Reservation Area: 3500 sq. miles NGL: 32 MMBNGL Wind River Reservation USGS Play Type Description of Play Oil or Gas Known Accumulations Undiscovered Resource (MMBOE) Play Probability Drilling depths Favorable factors Unfavorable factors Designation mean vol. oil, mean vol. gas, mean size, non assoc. (chance of success)

Basin Margin Subthrust 3501 Laramide basin-margin thrusting Both 50-200 BCF 31.1 MMBO (mean) 1 3,000 - 12,000 ft 1) confirmed play; new, ongoing 1) seismic delineation may prove has trapped oil/gas in upturned, exploration effort difficult 152 BCF (mean) overturned, folded, and faulted 2) thermally mature source rocks 2) field size could be small Phanerozoic strata below the 9.4 MMBO (mean field size) in portion of reservation 3) drilling mobilization may be 1 overthrust wedge. Multiple reservoir 6 BCF nonassociated gas 3) source rocks and reservoir present difficult horizons 4) multiple horizon exploration targets 4) drilling may be difficult

Basin Margin Anticline 3502 Anticlinal noses and domes forned Both 420 MMBO 19 MMBO (mean) 1 3,000 - 9,000 ft 1) confirmed play; production within 1) mature field development, new during the Laramide orogenic event. 525 BCFG 54 BCF (mean) reservation field development unlikely Best development along shallow margins 2) thermally mature source rocks 2) chance of hydrodynamic 3.6 MMBO (mean field size) of basin. Multiple reservoir horizons and 3) source rocks and reservoir present flushing of small structures 2 structural configuration 2 BCF nonassociated gas 4) seismic delineation is useful 3) possible small target size

Deep Basin Structure 3503 Intrabasin anticlinal, domal and fold Gas/condensate 15 MMBO 8.3 MMBO (mean) 1 9,000 - 14,000 ft 1) confirmed play; production exists 1) trapping mechanisms may nose structures within the deep,axial 1.3 TCFG 390 BCF (mean) on/near reservation be subtle, stratigraphic in part portion of the basin. Forned,enhanced 2) source rocks in oil-gas window, 2) new targets may be of 3.1 MMBO (mean field size) during the Laramide Orogeny with possible generation of gas probable smaller areal extent 3 older precursors. Multiple reservoir targets. 7 BCF nonassociated gas 3) source rocks and reservoir present 3) increased depths enhances 4) seismic may be very useful drilling difficulties/expense

Table WR 7.2 - Summary of play information.

Wind River Reservation GEOLOGY OVERVIEW Page 7 of 18 Wyoming Play Summary Reservation: Wind River Total Production ( by province-1996) Wind River Basin Undiscovered resources and numbers of fields are Geologic Province: Central Wind River Oil: 550 MMBO for Province-wide plays. No attempt has been made Province Area: Wind River Basin (11,700 sq. miles) Gas: 2.8 TCFG to estimate number of undiscovered fields within the Reservation Area: 3500 sq. miles NGL: 32 MMBNGL Wind River Reservation USGS Play Type Description of Play Oil or Gas Known Accumulations Undiscovered Resource (MMBOE) Play Probability Drilling depths Favorable factors Designation Oil Volume, Gas Volume, Field Size (chance of success) Unfavorable factors Muddy Sandstone 3504 Unconformity bounded pinch-outs Both 32 MMBO 58.6 MMBO (mean) 1 4,000 - 12,000 ft Stratigraphic 1) confirmed play; 1) discontinuous, complex of discontinuous Muddy Sandstone 160 BCFG 350 BCF (mean) production within reservation reservoir target intervals provide trapping 7.3 MMBO (mean Field size) 2) thermally mature source rocks 2) rough topography mechanisms. Stratal framework is 4 BCF nonassociated gas 3) source rocks and reservoir present 3) narrow play area 4 4) seismic delineation possible 4) seismic may not be helpful complex and distribution controlled 5) sequence stratigraphic interpretations useful by paleotopography and sea-level fluctuations.

Phosphoria Stratigraphic 3506 Porous, detrital carbonate tidal Oil > 1 MMBOE 12 MMBO (mean) .80 7,000 - 13,000 ft 1) confirmed play near reservation 1) limited production from channels of the Ervay member of no gas volume area interval the Phosphoria form possible reservoirs. 4.5 MMBO (mean field size) 2) thermally mature source rocks 2) reservoir facies may not 3) source rocks and reservoir be present in reservation area Fine-grained carbonates/shales provide interbedded 5 lateral and vertical seals. The reservoirs 3) limited well penetrations to 4) favorable migration pathways interval are adjacent to mature/organic-rich source rock.

Bighorn wedge-edge 3509 Wedge-edge pinch-outs of the unknown no information very high risk, no .05 8,000 - 13,000 ft 1) Thermally mature source rocks pinch-out 1) No production within Ordovician Bighorn Dolomite which available calculated estimates 2) Porosity could range up to 18% reservation abut against the base of the Madison 3) 'Bright' seismic character, easy 2) variable, discontinuous porosity to identify horizon Limestone could provide a trapping 3) lack of well control 6 mechanism. Dolomites can contain 4) small areal extent of targets 5) seismic may not be useful abundant intergranular porosity.

Flathead-Lander & 3510 Stratigraphic pinch-outs of unknown no information very high risk, no .05 10,000 - 14,500 ft 1) continuous sandstone lenses equiv. sandstone 1) lack of well control Cambrian Flathead and Ord. available calculated estimates 2) thermally mature source rocks 2) complex migration pathways Lander Sandstones could provide 3) high volume reserves if present 3) porosity highly variable a trapping mechanism. Variable 4) stratigraphic play, seismic of 7 reservoir quality. limited use 5) drilling depths/expense

Madison Limestone 3511 Porosity variation and topography unknown no information high risk, no .10 7,000 - 11,500 ft. 1) karst related porosity typically 1) lack of well control Stratigraphic related to karst development within available calculated estimates high 2) complex migration pathways the Madison Limestone could be 2) thermally mature source rocks 3) porosity highly variable a viable exploration target. 3) seismic may be very useful in 4) stratigraphic play, seismic may 8 picking karst horizons not be useful in structurally 4) 'bright' seismic reflector very disturbed areas 5) drilling depths/expense

Darwin - Amsden unknown 3512 Stratigraphic entrapment of no information high risk, no .10 7,000 - 11,000 ft. 1) sandstone porosity variable, but 1) porosity highly variable Stratigraphic hydrocarbons in discontinuous available calculated estimates could range up to 16% 2) complex migration pathways sandstones of the Penn. Darwin 2) thermally mature source rocks 3) no established production and Amsden Formations may be 3) large, areal extent of sandstone 4) stratigraphic play, seismic may possible. Unknown to variable lenses not be useful in structurally 9 reservoir quality very disturbed areas

Triassic & Jurassic 3513 Stratigraphic traps may exist in unknown high risk - no .10 6,000 - 10,000 ft Stratigraphic no information 1) porosity may be high 1) discontinuous, complex truncations and pinchouts of calculated estimates 2) thermally mature source rocks reservoir target Triassic and Jurassic aged 3) source rocks and reservoir present 2) rough topography sandstones. Complex stratigraphy, 4) seismic delineation possible 3) narrow play area 10 but possible good reservoir 5) sequence stratigraphic 4) seismic may not be helpful quality. interpretations usful

Shallow Tertiary-Upper 3515 Stratigraphic and modified Oil/gas > 1 MMBOE no oil volume .70 2,500 - 8,000 ft 1) confirmed play near reservation 1) limited production from Cretaceous structure/stratigraphic trapping 72 BCF (mean) area interval mechanisms in arkosic/lithic unknown (mean field size) 2) thermally mature source rocks 2) areal extent of target may be sandstones of Tertiary and Upper 3) source rocks and reservoir 3.0 BCF nonassociated gas small 11 Cretaceous age. Humic-rich source interbedded 3) seismic may not be useful in rocks adjacent to possible reservoirs. 4) favorable migration pathways structurally distrubed areas

Cody and Frontier 3518 Deep basin stratigraphic traps of unknown no information high risk, no .10 8,000 - 13,000 ft 1) Thermally mature source rocks Stratigraphic 1) No production within Upper Cretaceous Cody and calculated estimates 2) Porosity could range up to 15% reservation Frontier fine-grained sandstones. 3) clastic, sandstone reservoirs 2) variable,discontinuous porosity Mowry shale source horizons 3) lack of well control 12 interfingered within sandstones. 4) small areal extent of targets 5) seismic may not be useful

Basin Center Gas high risk, no 3505 Extensive and continuous gas no information .20-.70 11,000 - 14,500 ft 1) continuous accumulations 1) lack of well control overpressured gas accumulations calculated estimates but 2) thermally mature source rocks 2) complex migration pathways trapped in low permeability Paleocene volumes of gas in excess of 3) high volume reserves if present 3) porosity / permeability - low and uppermost Cretaceous reservoirs 2 TCF possible 4) stratigraphic play, seismic of 13 in deep parts of basin. Characterized limited use by overpressuring due to active generation of gas. 5) drilling depths/expense Table WR 9.1 - Play summary information. unconventional/hypothetical play conventional play

Wind River Reservation GEOLOGY OVERVIEW Page 8 of 18 Wyoming Play Summary (continued) Basin Margin Subthrust Play PLAY TYPE 1 buried Mesozoic and Paleozoic potential reservoir horizons could be Basin Margin Subthrust Play involved. Principal reservoirs include the Pennsylvanian Tensleep, Wind River Basin, Wyoming Permian Phosphoria carbonates, and Upper Cretaceous Frontier, Mesaverde, and Lance Formations. Source horizons could be from ￿ Laramide basin-margin thrusting has trapped oil and gas in the Phosphoria, Mowry, or Tertiary Fort Union Formations. It is State Line upturned, overturned, folded, and faulted Phanerozoic strata below likely that the shallower horizons would receive significant Sheridan the overthrust wedge. The limits of this demonstrated play are contributions from the Upper Cretaceous/Tertiary source intervals defined by the leading edge of basin-margin thrust faults and an Big Horn due to the simpler migration pathways. assumed overhand displacement of 6 mi. This is a currently Because Laramide thrust faults have thrust thick wedges of Park developing exploration play (Cave Gulch discovery) with previous Precambrian rocks over younger Paleozoic and Mesozoic intervals, exploration success limited to the Tepee Flats field. The Tepee Flats Basin outline the depth of burial of the source intervals is usually great enough for Johnson field is currently producing gas from the Frontier Formation at a Washakie source rocks to have generated hydrocarbons locally or for Play outline depth of about 12,200 ft. with a known recoverable of 9.0 BCFG hydrocarbons to have migrated from mature areas in deeper parts of Hot Springs Oil well (see Figures WR 10.2 & 10.3). Since this play has only been the basin during/after Laramide deformation (Figure WR 10.3). Gas well marginally explored, significant new reserves could be anticipated Some pre-Laramide migration may have taken place, moving Dry hole from this play type. The Cave Gulch discovery attests to the hydrocarbons into reservoirs before tectonic development of the economic viability of this concept with known recoverable Natrona basin-margin folds and faults. In this case, stratigraphic traps could Fremont estimates ranging from 50-200 BCFG (Fig. WR-10.1). Sparse Cave Gulch have formed prior to basin-margin thrusting and folding. Discovery information has been published regarding this new discovery but it Subsequent structural development could have re-mobilized is thought that relatively 'shallow' (>10,000 feet) Upper Cretaceous previously trapped hydrocarbons or kept the previous trap intact reservoirs contain the gas reserves. In the reservation area, little Sublette with a structural overprint enhancing the original trapping exploration has occurred over the potential subthrust areas. Wind River mechanism. Reservation Reservoir type and quality are highly variable since any of the

Carbon West A A' East Sweetwater Moncrief Wind River Tepee Flats 16-1 Casper 0 100 200 North 10,000 Basin Arch Miles

Figure WR-10.1 - Play outline for the Wind River Basin Margin Subthrust Play. Approximate location and type of penetrations in play outline located on figure. County and reservation outline depicted as well (from U.S.G.S. 1995 National Assessment). 0 0 Tertiary

￿ Petroleum is trapped where structures with closure occur Owl Creek beneath the basin-margin thrust and is sealed by associated Range -10,000 -10,000 rocks or by impermeable rocks of the hanging wall thrust Madden sheet. In the thrusting process the underlying beds are folded Gas Field Mesozoic and often upturned or overturned with fault slivers typically A' 19733 present (Figure WR-10.3). Oil and gas may also be trapped in 16-1 Moncrief these upturned, overturned, faulted, and folded strata. Depth Casper Wind River A Arch of production is highly variable, ranging from more than -20,000 Precambrian -20,000 20,000 ft. on the structurally steepest side of the asymmetrical Basin basin to less than 10,000 ft. in other basin-margin areas. Paleozoic

0 6 12 Miles -30,000 -30,000

Figure WR-10.2 - Location of adjacent Subthrust play Figure WR-10.3 - Subthrust structure on Casper arch could be similar to Madden field northwest of Moncrief 16-1 example along the eastern margin of the Wind River Tepee Flats discovery well. This structure is an symmetric fold related to compression of Owl Creek Range. Similar Basin (from Gries, 1983). subthrust structure may be present in the reservation area (after Gries, 1983).

Wind River Reservation CONVENTIONAL PLAY TYPE 1 Page 9 of 18 Wyoming Basin Margin Subthrust PLAY TYPE 2 Basin Margin Anticline Play Basin Margin Anticline Play Diagrammatic cross-section of Wind River Basin, Wyoming Sage Creek Anticline ￿ This mature exploration play is defined by the State Line occurrence of oil and gas trapped in anticlines and domes, in 2,000m Sheridan many cases faulted, and in faulted noses that formed during Chugwater Group major thrust movement in the Laramide orogeny. These Cody Shale Big Horn structures are best developed along the shallow margins of Park 1,000m the basin, with production ranging from about 1,000 ft. to Lower Cretaceous 14,000 ft. The inner boundary of the play is located at the Cambrian Basin outline Johnson Base Cretaceous Washakie approximate basinward limit of basin-margin anticlines (Fig. Play outline WR-11.1). The outer boundary is drawn at the outcrop edge Hot Springs Oil well sea level of the Tensleep Formation. Chugwater Top Paleozoic Group Gas well ￿ Basement-involved and basement-detached thrusting has Dry hole produced complex folded/faulted anticlines, domes, and Natrona synclines. These surface features were drilled early (1900- -1,000m Cambrian Fremont 1950's) in the exploration history of the Wind River Basin. Figure WR-11.4 shows an example of a typical basement- Sublette involved thrust/fold pair showing development of subsidiary Precambrian faults and upturned fault sliver. In this case, the Sage Creek -2,000m Wind River Reservation Anticline has only produced minimal hydrocarbons. Figure (no vertical exaggeration) WR-11.5 shows the development of a typical detachment Figure WR-11.4 - Basement-involved fold-thrust structure development. Subsidiary fault structure; detachments usually occur in Triassic or Jurassic- development, usually detachment features. Example of complex fault-propagation fold fold model aged sediments. typical of foreland uplifts (modified from Willis & Groshong, Jr., 1993). Carbon ￿ Major fields have been discovered in these complex Sweetwater thrust/fold structures. Circle Ridge contains multiple 0 100 200 North reservoir horizons ranging from the Madison to Phosphoria Miles Formations (Figure WR-11.2). This is typical for this play type. Because of the shallow nature of some of these Figure WR-11.1 - Play outlines for the Basin Margin Anticline Play in the Wind River Basin. Approximate locations of structures and close proximity to outcrop, tilted oil/water well penetrations in play area noted (from U.S.G.S. 1995 National Assessment). contacts are common due to flushing from nearby recharge Windrock Ranch Anticline SW NE areas (Fig. WR-11.2). Care must be taken in evaluating the Major Fields located within Reservation hydrodynamic conditions of potential targets in this play Cretaceous Riverton Dome ￿ ￿ 180 BCFG, 510 MBO Lander￿ 20 MMBO type. Steamboat Butte ￿ ￿ 95 MMBO Pavillion￿ 174 BCFG Winkleman Dome￿ ￿ 98 MMBO Maverick Springs￿ 10 MMBO Circle Ridge￿ 29 MMBO Muddy Ridge ￿ 29 BCFG Yellowstone Cretaceous Jurassic

National Big -100m Powder Jurassic Park Horn Basin River Circle Ridge Gypsum Sundance Field Basin SW NE Windrock Ranch Spgs. Recharge Jur/Triassic Form. Anticline Wind 9000' area 9000' Circle Ridge Sage Creek River Casper Nugget Anticline 8000' 8000' Sandstone 7000' Mowry Sh. 7000' 6000' 6000' Green Denver 5000' Chugwater Grp. 5000' Rock Schematic Cross-Section River Springs Basin 4000' Phosphoria 4000' Cheyenne Hydrocarbon producing through Circle Ridge Basin Figure WR-11.5 - Example of basement-detached folding and faulting in Laramide- Tensleep zone 3000' Amsden Field 3000' aged structures. Note development of smaller-scale anticline/syncline pair (pop-out Madison Wyoming Location Map anticline) developed in the center of syncline. Example of fold-thrust deformational 2000' 2000' style typical of foreland uplifts (after Willis & Groshong, Jr., 1993). Figure WR-11.3 - Location map for areas depicted on page (after Figure WR-11.2 - Generalized cross section from southwest to northeast through northern portion of Circle Ridge Anticline Anderson & O'Connell, 1993). showing its topographic and hydrodynamic setting. Faults not shown; no vertical exaggeration (after Anderson & O'Connell, 1993).

Wind River Reservation CONVENTIONAL PLAY TYPE 2 Page 10 of 18 Wyoming Basin Margin Anticline PLAY TYPE 2 (continued) Yellowstone National Big Basin Margin Anticline Play Powder Park Horn Basin River ￿ Examples from the Circle Ridge Field illustrate the nature of this particular ￿ Pre-Laramide generation and long-distance migration from western Circle Ridge Field play type within the Wind River Basin. Producing formations range in age from Wyoming prior to basin formation, followed by remigration during the Laramide Basin Mississippian through Cretaceous and include Madison, Tensleep, Phosphoria, Orogeny, is a possibility for charging lower Paleozoic reservoirs. However, Windrock Ranch Anticline Wind Sundance, Nugget, Cloverly, Muddy, Frontier, Cody, and Mesaverde local generation of deeply buried Cretaceous source rocks is a likely mechanism Sage Creek River Casper Formations (see Figure WR-12.3). Primary production has been from the for charging reservoirs as well. Anticline Beaver Madison, Tensleep, and Phosphoria Formations. Many of the fields have ￿ Structural closure in faulted anticlines, domes, and noses is the predominant Creek multiple pay zones and some show common oil-water contacts involving several trapping mechanism for this play. Figure WR-12.2 illustrates the typical of the Paleozoic reservoirs. Sandstone is the dominant reservoir lithology. thrust/fold structural pattern found in this play type. The shallower portions of ￿ Paleozoic reservoirs contain hydrocarbons derived from a distinct these structures tend to become structurally more complex due to subsidiary Green Denver Phosphoria source facies. Two fields in the western part of the basin, Circle fault development along the major thrust horizons. While the deeper, larger Rock River Springs Basin Ridge and Beaver Creek, produce oil from the Madison Limestone (see Figure areas of structural closure may have been thoroughly explored, the smaller, Basin Cheyenne WR-12.1). Properties of the oil in these two fields are nearly identical to those shallower structural compartments should offer significant potential for future of the Tensleep and Phosphoria oil in the same area, indicating that the oil may exploration. Wyoming Location Map have been derived from the younger Phosphoria source or re-mobilized from younger reservoir horizons. Figure WR-12.3 depicts the structural position of Figure WR-12.1 - General location map showing position of Wind River the Phosphoria in relation to other reservoir horizons; additional throw in the Basin and Circle Ridge Field. structure could easily juxtapose Madison against known source intervals or reservoirs.

Figure WR-12.2 - Structure 36 31 contour map of Circle Ridge 5500 5500 Circle Ridge Field on top of the Phosphoria Circle Ridge Field Formation. Shows position of 5750 Field Cross Section A - A' 6000 thrusts at depth, A' 6250 compartmentalized behavior of A reservoirs, and fairly simple 6500 5750 A' structural closure at 'deep' Phosphoria level (after Mowry 6500 Anderson & O'Connell, 1993). Sundance 6250 Cloverly/Thermopolis Tensleep Morrison Amsden

6500

A Chugwater Grp. Madison 7250 Phosphoria 1 6

Morrison Amsden

7000 Bighorn Frontier Madison

6750 Mowry

Sundance Phosphoria 6500 Cambrian Cambrian Phosphoria 6250 Structure Map 6000 Chugwater Grp. Tensleep 5750 Flathead Ss. contour interval = 50' Basement

12 7 Figure WR-12.3 - Stratigraphic/structural reconstruction of outcrop and well data through a northern cross-section of Circle Ridge Field. See Figure WR 12.2 for cross- section location. This field is typical of the basin margin anticline structures found in this play. Multiple reservoir horizons, compartmentalized reservoirs and flow units, 5280' = 1 mile and complex fluid pathways are common in this type of play (modified after Anderson & O'Connell, 1993). Scale Wind River Reservation CONVENTIONAL PLAY TYPE 2 Page 11 of 18 Wyoming Basin Margin Anticline Play (Continued) Deep Basin Structure Play PLAY TYPE 3 Most fields have multiple pool production from a great range of Wind River Basin, Wyoming Deep Basin Structure depths and thicknesses. Most individual reservoir intervals range between 25-50 feet in thickness. Reservoirs may be overpressured; for example most Tertiary and Mesozoic strata on the Madden structure are State Line ￿ This is a demonstrated gas play with entrapment in large intrabasin overpressured but nearly normal pressure gradients occur near the top of Sheridan anticlinal, domal, and fold nose structures within the deep axial portion of the Paleozoic interval. Big Horn the basin. The boundary of this play is defined on the north by the leading Most of the productive reservoir intervals are interbedded with edge of the northern basin-margin thrust fault and on the south and west by source rocks. This facilitates migration and entrapment of the Park the deep limit of the Basin Margin Anticline Play. hydrocarbons. Indigenous source rocks are found in the Permian Basin outline ￿ Reservoir rocks range in age from Mississippian to Eocene. The bulk of Phosphoria, Cretaceous Mowry, and Tertiary Fort Union (including Johnson Play outline the gas production has been from Lance, Fort Union, Wind River, and Washakie Waltman shale) Formations. Early Paleocene generation from the Fort Oil well Mesaverde Formations. However, deeper drilling has encountered Union sources has been modeled using vitrinite reflectance data. Hot Springs Gas well significant reserves in the Mississippian Madison and Pennsylvanian Generation probably continues to present and accounts for some of the Dry hole Tensleep Formations. Porosity and permeability reduced through overpressured intervals encountered in some fields. compaction/cementation with deeper burial, may be re-enhanced by Potential for undiscovered resources may be good-excellent in this fracturing and secondary cement dissolution. Early migration and Natrona play due to deeper pool discoveries. Madden Field (825 BCFG), Pavillion entrapment may have preserved some of the original porosity. Even if the (174 BCFG), Waltman-Bull Frog (96 BCFG), and Frenchie Draw (46.5 hydrocarbons have been re-mobilized due to movement associated with the BCFG) all have the potential for deeper reservoir horizons. In fact, many Fremont Laramide Orogeny, the porosity and permeability may have been of the currently discovered fields do not include Paleozoic units such as the Sublette preserved. This would allow subsequent migration into reservoir intervals Madison Limestone, which is a major new reservoir at Madden Field. Wind River from source rocks that initiated generation/expulsion in late Paleocene Reservation through to the present time.

Pavillion Field Wind River Basin Datum - Fort Union Formation Carbon R 2 E R 3 E Sweetwater 0 100 200 North Pavillion Field Parameters Miles 1900

25 30 Formations: ￿ Fort Union & Figure WR-13.1 - Well distribution, play outline, and location of the Deep Basin Structure 1700 1800 Wind River Fm. Play in the Wind River Basin (from U.S.G.S. 1995 National Assessment). T 2000 Lithology: ￿ sandstone 4 N Porosity: ￿ 20% av., range 4-28% Permeability:￿ av. 3 md, range Figure WR-13.2 - Major field 36 31 from 0.1 - 300 md 1600 distribution in the Wind River 1800 Pay thickness:￿6-50 feet 1900 Wind River Basin. Fields producing from Oil/Gas column: 400-500 feet Deep Basin Structure plays Gas/Oil Ratio:￿ almost 100% dry ￿ Owl Creek Mountains Basin and noted (from Johnson & Rice, methane gas Reservation 1993). 1 6 Circle Ridge Depths: ￿ 3000-12,000 feet Maverick subsea Sheldon Spring Dome West Sheldon Muddy Ridge Other: Deeper pools in both Dome Sand Pavillion and Madden Steamboat Mesa Fields have been Butte 12 7 Wind River Range Madden Casper Arch found in the Pavillion Boysen Frenchie Pilot 2000 Miss. Madison, Butte Fuller Reservoir Draw T 1900 Indian Butte Waltman 3 Cretaceous Frontier, Winkleman Haybarn Figure WR-13.3 - Structure Bull N Cody, and Mesaverde Dome Riverton Dome E. Cooper contour map of Pavillion Field. 1800 Frog Formations. Riverton Reservoir Datum is top of the Fort Union 1700 Lander Alkali Butte N. Wallace Creek 1500 Dome Castle Formation. This structure 13 1600 18 Gardens Alkali Grieve N. illustrates the typical domal - Butte 1400 Dallas Dome Beaver Creek Muskrat anticlinal nose structural Big Sand Draw Grieve orientation of this play type. Derby Note absence of major fault Granite Mountains Oil Field horizons - blind thrust probably Dome 24 19 Location of oil and gas fields 0 40 Gas Field at depth (after Wyoming 1400 from the Deep Basin Structure Play Miles Oil & Gas Field Geological Assoc., 1982). Gas well CI = 50 feet

Wind River Reservation CONVENTIONAL PLAY TYPE 3 Page 12 of 18 Wyoming Deep Basin Structure Play Muddy Sandstone Play PLAY TYPE 4 Wind River Basin, Wyoming Muddy Sandstone Stratigraphic Play ￿ Migration from adjacent Mowry source rocks provides efficient pathways for fluid migration. This demonstrated play is heavily explored along the southern margin of State Line ￿ This is a stratigraphic play with anticipated entrapment of Sheridan oil/gas in updip pinchouts of discontinuous Muddy Sandstone the basin but is lightly explored in the central or western regions. Relatively new bodies, deposited as a complex series of coastal/valley-fill discoveries at Austin Creek (1988) and Sun Ranch (1987) indicate that additional Big Horn sandstone horizons whose distribution is controlled by exploration opportunities are possible. Park Basin paleotopography and sea-level fluctuations. Actual outline of ￿ The reservation area is ideally situated to capitalize on new target possibilities outline play area may be unknown due to subtle nature of some within this play. Application of improved seismic processing techniques, sequence Johnson Play channel/coastline complexes on seismic (Figure WR-14.1). stratigraphic principles, and fluid migration modeling could greatly enhance the Washakie outline ￿ The Muddy Sandstone and equivalent strata have produced future potential within this play type. Hot Springs Oil well more than 1.7 billion bbl of oil-equivalent hydrocarbons in the Gas well Dry hole Rocky Mountain region. Production is controlled principally by unconformities formed during a relative sea level lowstand. Natrona Fremont Reservoirs are found in paleohills of older marine sandstones, younger valley fill and associated alluvial plain channel sandstones, and infilling transgressive marine deposits (see Sublette Marine Figures WR-14.3 and WR-14.4). Foreland Wind River ￿ Valley fill and channel reservoirs have produced at least 359 Bow Basin Reservation MMBOE, onlap cycles another 318 MMBOE, and older marine Island Deltas Cedar Creek buried-hill reservoirs more than 269 MMBOE. The excellent Sevier High Orogenic reservoir characteristics and the high quality of oil (33-43 API Belt gravity) make it a prime drilling objective. Porosity ranges from Carbon Cratonic Sweetwater about 9% - 15% at depths to about 11,000 ft. Most reservoirs Source 0 Muddy to East 100 200 North range between 20 - 52 ft. in thickness. Deltas Miles

Bell Creek High Figure WR-14.1 - Play outline for the Muddy Sandstone Play showing distribution of dry holes, oil and (A) T1 Ancestral gas wells, and reservation outline (from U.S.G.S. 1995 National Hydrocarbon Assessment). T2 Bighorns

Sweetwater Uplift

Ancestral Belle Fourche Arch

Ancestral Rock T1 & T2 Springs Uplift Bear River Alluvial Fans (B) (Not palinspastically Hartville Uplift Wind River Erosional restored) Surface Owl Creek Mountains Basin and Regional Drainage Divide Reservation Drop in Circle Ridge sea level Maverick Sea Level Sheldon Spring Dome West T3 Sheldon Muddy Ridge Ephraim Dome Sand Conglomerates Steamboat Mesa (C) Wattenberg High Butte Rise in Wind River Range Madden Casper Arch Pavillion Boysen Frenchie sea level Dakota Pilot Indianola Group equiv. Butte Fuller Reservoir Draw Indian Butte Waltman Winkleman Haybarn Erosional edge of Bull Dome Riverton Dome E. Cooper Skull Creek Shale Frog Mogollon High to Riverton Reservoir Lander Alkali Butte N. Wallace Creek Southwest Dome Castle T4 Gardens Wild Horse Eroding Paleozoic source Alkali area in Arizona/Utah Butte Grieve N. Butte Dallas Dome Beaver Creek Muskrat Sun Ranch Grieve Big Sand Draw Trend of Coarsening-upward log signatures Derby Conglomerates and alluvial fan deposits Granite Mountains Figure WR-14.3 - Generalized alluvial valley model applicable 0 100 200 Dome Present Precambrian outcrops miles Location of oil and gas fields to the Muddy Formation (Weimer, 1983). (A). Initial wave- Wind 0 40 River from the Muddy Sandstone Play Generalized paleocurrent direction Miles dominated deltaic progradation during highstand (B). T3 time Area depicts truncation of older marine and deltaic deposits with Drainage patterns of Muddy Formation channels Figure WR-14.2 - Distribution of fields within the Wind River Basin that are producing from the Muddy Sandstone continued sea level lowering (C). T4 time shows relative sea Play type. Small fields > 1 MMBO are not shown on diagram (modified from Johnson & Rice, 1993). level rise and backfilling of valley networks with fluvial/ marine Figure WR-14.4 - Muddy Sandstone drainage networks developed at maximum sea level lowstand. strata ( Dolson, et al,1991). Paleocurrent directions shown are derived from cross-bedding in fluvial strata. Note position of general reservation area relative to channel networks and deltas (from Dolson, et al, 1991).

Wind River Reservation CONVENTIONAL PLAY TYPE 4 Page 13 of 18 Wyoming Muddy Sandstone Stratigraphic Play PHOSPHORIA STRATIGRAPHIC PLAY Stratigraphic Column Wind River Basin, Wyoming Isopach Map of Retort Shale Member for of Phosphoria Formation Wind River Reservation State Line > 10 ft. of Ervay Member Sheridan Area where carbonate porosity < 10% Big Horn > 20 ft. of Ervay Member Park where carbonate porosity < 10% Paleogene & Neogene Undifferentiated

Basin outline Wind River Fm Johnson Eocene Washakie Play outline Indian Meadows Fm Hot Springs Oil well Evaporite

Cenozoic Paleocene Fort Union Fm Gas well Facies TERTIARY S Dry hole North Limit of Lance Fm Natrona Permian rocks Fremont Meeteese Fm 0 Mesaverde Ss

Sublette 50 Upper Cody Sh Montana Wind River Frontier Fm Reservation Approx, location of Wyoming Mowry Sh Wind River Reservation25 S

25 CRETACEOUS Muddy Ss 100 Thermopolis Sh

Carbon 75 Lower S Sweetwater

Mesozoic Cloverly Fm 0 Evaporite 100 200 North Tectonic Miles 25 Facies Morrison Fm Disturbed50 Zone 25 75 JURASSIC Sundance Fm Figure WR-15.1 - Play outline for the Phosphoria Stratigraphic Play showing distribution of dry 50 holes, oil and gas wells, and reservation outline (from U.S.G.S. 1995 National Hydrocarbon Gypsum Springs Fm Assessment). Nugget Ss Carbonate Evaporite TRIASSIC Chugwater Gp Facies PLAY TYPE 5 75 Facies Dinwoody Fm PERMIAN Phosphoria Stratigraphic Play Redbed Mudstone Phosphoria Fm S 50 Facies PENNSYLVANIAN Tensleep Ss 25 ￿ High sulfur oil may be stratigraphically trapped in the Ervay Member of the Phosphoria Amsden Fm 0 Formation along a north-south transition zone from Phosphoria carbonates to the west and 25 MISSISSIPPIAN Madison Ls red shale and evaporites to the east (Fig. WR-15.2). The play area is located in the eastern ORDOVICIAN Bighorn Dol

Wind River Basin, limits of the play defined to the east by the eastern limit of the Ervay Paleozoic Figure WR-15.2 - Map showing thickness of Retort Phosphatic Shale Member of Phosphoria Gallatin Ls Member, to the west by the estimated limit of viable carbonate porosity, and to the north Formation (Lower Permian), and distribution of carbonate porosity greater than 10 percent in the Ervay Gros Ventre Fm and south by Phosphoria outcrops (Fig. WR-15.1). Member (from J. Peterson, 1988). CAMBRIAN ￿ Potential reservoir intervals occur in the Ervay Member of the Phosphoria Formation. Flathead Ss PLAY TYPE 6 They are typically dolomitized grainstones and packstones, along with algal framework PLAY TYPE 7 PRECAMBRIAN Undifferentiated laminations containing abundant fenestrate porosity. These reservoir intervals formed in Bighorn Wedge-Edge Pinchout Play Flathead-Lander and Equivalent high-energy tidal and shoreline environments. Reservoir matrix porosities average about 10 Sandstone Stratigraphic Play Source horizon percent, but are fracture enhanced due to generation of hydrocarbons in-situ. Reservoir ￿ This is a hypothetical play concept characterized by S thicknesses range between 25 - 75 feet. wedge-edge pinchouts of the Ordovician Bighorn Oil Gas Production from reservoirs ￿ The interbedded nature of the carbonate facies with known source facies in the dolomite against the base of the Madison Limestone ￿ This is a hypothetical play concept which involves in approx. proportions Phosphoria may create efficient migration pathways into reservoir horizons. Exploration in (Fig. WR-15.3). This is a very high risk play with no hydrocarbons trapped in stratigraphic facies this interval was initiated back in 1953 with the discovery of the Cottonwood Creek Field in known hydrocarbon occurrences or source rocks to change/erosional truncation horizons within the Figure WR-15.3 - Stratigraphic column for the Wind River Basin occur near/within the potential trapping horizon. Cambrian Flathead and Ordovician Lander Sandstones depicting general distribution of major source intervals and reservoir the Bighorn Basin. This large field has known reserves of 59 MMBO and 42 BCFG. horizons. Subsequent discoveries in the Bighorn Basin have been small and infrequent. Exploration ￿ Reservoirs in the Bighorn Dolomite could contain (Fig. WR-15.3). No known hydrocarbon occurrences success in the Wind River Basin has been of limited extent, and only one or two very small moderate-high porosities within an intergranular fabric. or source intervals are known within these formations. accumulations have been found to date. Dolomitized intervals within this formation are very ￿ Potential reservoir intervals could occur in ￿ Stratigrapahic traps should occur near the edge of the carbonate facies in the Ervay common and anticipated to occur throughout most of sandstones which are probably present throughout Member; in porous, detrital reservoirs deposited within the high energy regimes of tidal the reservation area. Although regional truncation is much of the reservation area. Quality of potential

channels on coastal tidal flat environments. Updip seals are provided by fine-grained demonstrated, the presence of traps at this reservoirs may be poor due to diagenesis and carbonates of intertidal/supratidal origin. The facies change from carbonates to the west, to unconformity horizon is undocumented. compaction. The absence of known source intervals red mudstone/evaporites could be thought of as a regional/lateral sealing configuration. near these reservoir horizons implies that the chance of Depth to producing horizons could range from 2,000 - 20,000 feet. exploration success is minimal.

Wind River Reservation UNCONVENTIONAL PLAY TYPES 5,6,7 Wyoming Phosphoria Stratigraphic, Bighorn Wedge-Edge Pinchout Page 14 of 18 Flathead-Lander and Equivalent Sandstone Stratigraphic Plays PLAY TYPE 8 PLAY TYPE 9 Madison Limestone Stratigraphic Play Darwin-Amsden Sandstone Stratigraphic Play

Western Limit ￿ This hypothetical play encompasses possible hydrocarbons ￿ This hypothetical play consists of stratigraphic entrapment of oil in discontinuous of Charles Salt enclosed within or at the top of the Mississippian Madison sandstone lenses of the Pennsylvanian Darwin and Amsden Formations. Although no Approx. limit Limestone. The trapping mechanism involves a combination of known traps exist within the Wind River Basin, these formations are productive elsewhere of Bakken Formation porosity variation and topography creation related to karst in structural settings. development. ￿ Potential reservoir intervals in poor-moderately porous sandstones are believed to be ￿ Karstic, vuggy porosity carbonate intervals in the upper part of present over most of the reservation area. Total interval thickness ranges between 100 - 300 the Madison Limestone are expected throughout the play area feet (Figure WR-16.2). Variable quality of porosity and permeability are expected and may (Figure WR-16.1). In some cases, these intervals may be fracture be modified by burial diagenetic processes. ? enhanced. The presence of sealing horizons above the Madison ￿ Hydrocarbon charging of this interval is problematic and would require complex, remain problematic. In addition, to charge these potential reservoirs structurally modified, migration pathways. In addition, poor seal quality is expected

Montana ? requires fault juxtaposition of Phosphoria source against Madison. immediately above the horizon. This requires advantageous timing of hydrocarbon generation, ￿ No production exists within this play type and it is classified as a high risk exploration Wyoming structural development, and migration. target. Considerable variation of sandstone distribution and porosity exists within the Approx, location of ￿ No production exists utilizing this play concept within the Wind interval; detailed facies mapping of the Amsden as well as detailed structural modeling Wind River Reservation ? River Basin and the presence of effective traps has not been would be required to effectively explore for hydrocarbons.

Tectonic demonstrated. As a result, this play type is classified as very high risk owing to poor charge and trap potential. Detailed mapping of Disturbed Zone the Madison karst surface is required to evaluate the exploration Amsden and Big Snowy Group potential within the reservation area. Equivalents Isopach Map

500 thickness in feet

Carbonate Porosity Map of Madison Formation 0 > 100 ft. where carbonate 500 porosity > 10% > 200 ft. where carbonate 1500 Big Snowy Trough porosity > 10% 1000 PLAY TYPE 12 500 Figure WR-16.1 - Map showing distribution of net porosity greater than 10 percent in Cody and Frontier Stratigraphic Play 100 Madison carbonate rocks, approximate limit of Bakken Formation and equiv., and 100 reservation area (after J. Peterson, 1988). ￿ This hypothetical play would include deep oil and gas accumulations in stratigraphic traps from the Upper Cretaceous PLAY TYPE 10 Cody and Frontier Formations. These sandstone/shale intervals Montana are in thick marine sequences of shale and fine-grained sandstone. Wyoming Triassic and Jurassic Stratigraphic Play 0 ￿ Potential reservoir intervals of sheets of fine-grained 200 300 sandstone are present throughout the reservation area. Although ￿ This hypothetical play encompasses stratigraphic plays within the Approx, location of 200 Chugwater Group, Nugget Sandstone, Sundance, and Morrison equivalent reservoirs are productive in structural settings, Wind River Reservation reservoir quality and effective traps in deeper, off-structural Tectonic Formations. The Nugget Sandstone provides the best opportunity for 300 300 commercial production from wedge-edge pinchouts and truncations in settings remain speculative. Disturbed Zone ￿ Cretaceous source rock intervals in the Mowry Shale are the eastern and northern portion of the Wind River Basin. 500 interbedded with these potential reservoir horizons. A favorable ￿ Potential reservoirs would include mostly sandstone with good 200 hydrocarbon generation and migration history could charge these 100 porosity and permeability. Sealing horizons remain problematic as 700 100 100 well as the presence of effective hydrocarbon charge. reservoirs if an effective trapping mechanism is present. The presence of traps of significant size have not been demonstrated. 200 ￿ Numerous shows and non-commercial accumulations have been 300 300 found in these zones. They may act as migration pathways into other This play is characterized as high risk because of these issues. 500 horizons. This play is classified as high risk and would require 200 700 detailed stratigraphic/charge modeling to effectively explore for 1000 200 0 0 hydrocarbons from these intervals. 0 50 Miles

Figure WR-16.2 - Map showing thickness of Amsden Formation and Big Snowy Group equivalents (after J. Peterson, 1988).

Wind River Reservation CONVENTIONAL / UNCONVENTIONAL PLAY TYPES Wyoming Madison Limestone, Darwin-Amsden Sandstone Page 15 of 18 Triassic and Jurassic, and Cody/Frontier Stratigraphic Plays Shallow Tertiary-Upper Cretaceous Stratigraphic Play PLAY TYPE 11 Stratigraphic Wind River Basin, Wyoming Unit (Ma) Shallow Tertiary/Upper Cretaceous Stratigraphic Play Ages Series System or event (in feet) Thickness

mid-Mio. to present uplift and erosion -3,380 15 - 0 State Line Primarily a gas play, the shallow Tertiary and Upper Cretaceous reservoirs have Sheridan also yielded liquids as well in these discontinuous, sandstone reservoirs. This play has Split Rock 900 24 - 15 Formation

Big Horn been lightly explored for years and a number of small accumulations have been Miocene Park Basin discovered within/outside the reservation area (Figures WR-17.1 and WR-17.2). Outline ￿ In general, the proven reservoirs include the Wind River, Fort Union, Lance and White River 500 36 - 24 Formation Play Mesaverde Formations (Figure WR-17.3). These clastic sandstone reservoirs have Johnson Oligocene Washakie Outline good-excellent porosity and permeability, however, most exhibit discontinuous, Post lower Eocene 1,980 Hot Springs rocks-undivided Oil well fluvial reservoir architecture (Figure WR-17.4). Source horizons are 55 - 38 Wind River and Indian Gas well underlying/interbedded Cretaceous/Paleocene shales and coals. Humic-rich coal Tertiary Eocene Meadows Formations 4,625 Dry hole horizons may be contributing to the gas charge as well as other shale zones with undifferentiated Shotgun Natrona abundant Type III kerogen mixtures (Figure WR-17.2). In some instances, oil from the 2,175 59 - 55 Member Waltman Shale has accumulated in reservoirs of Upper Cretaceous through Eocene Waltman age. Shale 840 60 - 59 Fremont Member

￿ Facies changes and local erosional unconformities associated with channel Paleocene Sublette Lower 1,350 66 - 60 migration are the typical trapping mechanisms for these fluvial reservoirs. They are member

Wind River Fort Union Formation Reservation typically alluvial/fluvial sandstones that form localized channel bodies of limited areal extent (Figure WR-17.4). Traps are small and sometimes occur in combination with Lance Formation 2,200 74 - 66 structural enhancement. Seals are provided by associated fine-grained overbank shales. Fluid migration is primarily vertical. Meeteese Form. 800-1,000 79 - 74 Upper Carbon ￿ Stacking of multiple reservoir horizons is enhanced when the underlying Sweetwater Mesaverde Form. 1,200-1,800 84 - 79 0 100 Cretaceous Mesaverde Formation is unconformably overlain by younger Paleocene 200 North Cretaceous reservoirs. This also allows more efficient migration from source horizons within Miles Figure WR-17.3 - Stratigraphic column of Tertiary/Upper Cretaceous Upper Cretaceous/Paleocene intervals (Figure WR-17.5). stratigraphy in the reservation area of the Wind River Basin. Position of Figure WR-17.1 - Play outline for the Shallow Tertiary/Upper Cretaceous Stratigraphic Play showing distribution potential source interval is depicted in brown and intervals containing coal of dry holes, oil and gas wells, and reservation outline (from U.S.G.S. 1995 National Hydrocarbon Assessment). are depicted in dark gray (modified from Nuccio, V., 1994). N S

200 Hot Springs Co. Ft. Fremont Co.

Wind River T 6 Owl Creek Mountains Basin and N Reservation T Circle Ridge 5 Maverick N Sheldon Spring Dome West Muddy Ridge T Sheldon 4 Dome Sand N Steamboat Mesa Butte Wind River Range Madden Casper Arch T Pilot Pavillion Frenchie 3 Fuller Reservoir Draw N Butte Indian Butte Area where Mesaverde is Winkleman Waltman overlain by and in normal T Haybarn contact with the Meeteetse 2 Dome Riverton Dome E. Cooper Bull Formation N Frog Riverton Reservoir Mesaverde is overlain by Lander Alkali Butte N. Wallace Creek Fort Union or younger T Dome Castle 1 Gardens Wild Horse Overbank fluvial mudstones and siltstones Mesaverde is overlain by Riverton N Alkali Lance Formation Grieve N. Butte Dallas Dome Butte Muskrat Meandering and multi-storied fluvial channel systems T Beaver Creek Sun Ranch Mesaverde outcrop Fort Washakie Grieve 1 Big Sand Draw Overbank swamp/coal deposits S Derby Dome Granite Mountains Braided stream conglomerate deposits formed by R 3 E R 4 E R 5 E R 6 E Location of oil and gas fields 0 40 R 5 W R 4 W R 3 W R 2 W R 1 W R 1 E R 2 E from the Shallow Tertiary/U. Cretaceous Play drainage of nearby highland areas Miles 0 5 10 15 Figure WR-17.4 - Diagram showing typical stratigraphic framework and Miles Figure WR-17.2 - Distribution of fields within the Wind River Basin that are producing from the Shallow reservoir anisotropy of Paleocene Fort Union Formation. Note distribution of Tertiary/Upper Cretaceous Play type. Small fields > 1 MMBO are not shown on diagram (modified from Johnson coal and potential reservoir intervals (modified from Flores & Keighin, 1993). Figure WR-17.5 - Map showing distribution of Mesaverde Formation within the & Rice, 1993). Wind River Reservation. Juxtaposition against shallower horizons facilitates migration of hydrocarbons (from Keefer & Johnson, 1993).

Wind River Reservation CONVENTIONAL PLAY TYPE 11 Page 16 of 18 Wyoming Shallow Tertiary/Upper Cretaceous Stratigraphic Play Basin-Center Gas Play PLAY TYPE 13 ￿ Since active generation is occurring from most of the Tertiary/Upper Wind River Basin, Wyoming Basin-Center Gas Play Cretaceous humic-rich coals and shales, timing is extremely favorable with reference to the interbedded potential reservoir intervals. Overpressuring which is one result of the active generation of gas State Line ￿ This play is characterized by an extensive and continuous appears to generally coincide with Ro=1.0% burial indicator. This Sheridan overpressured gas accumulation trapped in low permeability Paleocene maturation indice is usually reached at about 10,000 feet. Therefore, Big Horn and uppermost Cretaceous sandstone reservoirs in the deep parts of the Wind River Basin (Figure WR-18.1). The play exists because the active those Tertiary andUpper Cretaceous intervals below this subsea elevation Park generation of gas from source intervals in the deep part of the basin could be considered potential exploration targets. Basin ￿ The limiting factors regarding the development of these reservoirs outline creates overpressuring. This allows reservoirs to be charged that would Johnson are principally economic; the price of gas and expense associated in Washakie Play outline otherwise be non-reservoir intervals due to low permeability and developing reservoirs with significant internal compartmentalization. Hot Springs Oil well porosity. ￿ Principal reservoirs are sandstone beds in the Fort Union, Lance and Therefore, this play is considered high risk even though active generation Gas well from source intervals is occurring at the present time. Dry hole Mesaverde Formations. They are generally arkosic or lithic in composition, with poor to modest porosity and low permeability (Table Natrona WR-18.1). Within the reservation area the reservoirs could be of three Fremont types; alluvial-fluvial sandstone bodies with channels of limited areal extent, marine sandstone intervals with a more blanket-like character, Sublette and overbank siltstone/silty sandstone crevasse splay deposits. Wind River ￿ Trapping mechanisms for this play concept are depicted in Figure Reservation WR-18.2. This play will only be viable if active generation is occurring to continuously replenish the reservoir intervals since most sealing intervals are 'leaky' with respect to gas in these environments. Transient Carbon sealing mechanisms are common in deep, basin-center accumulations. Sweetwater 0 100 200 North Miles Schematic diagram of trapping mechanism Figure WR-18.1 - Play outline for the Basin-Center Gas Play showing distribution of dry holes, oil and gas for Basin Center Gas Play Type wells, and reservation outline (from U.S.G.S. 1995 National Hydrocarbon Assessment). B L Outcrop Sandstones are water bearing except on structure and in local 'Tight' Gas 'Tight' Gas stratigraphic traps Table WR-18.1 Conventional Gas Blanket/Lenticular Sandstone Blanket Siltstone, Silty Shale Gas-water transition Sandstone (Low Pressure Reservoir) (High Pressure Reservoir) zone

Porosity (%)￿ 14 - 25+￿ 3 - 12+￿ 10 - 30+ in individual Conventional siltstone laminations Decreasing Permeability

Porosity Type￿ Primary￿ ￿ Common secondary￿ Dominantly primary, Main gas zone (intergranular), some￿ (microvug), some￿ ￿ some secondary Conventional B secondary￿ intergranular￿ L modified from C. Spencer, 1989 Porosity Communication￿ Good-excellent. short￿ Poor, relatively long, sheet/￿￿ Good, short pore throats, but gas impeded by clays, pore throats￿ ribbonlike capillary system￿ ￿ small size of pores, and high Sw

Relative Clay Content￿ Low￿ High to moderate￿ Low to High in Pores L Water filled reservoir Water Saturation (%)￿ 25 - 50 ￿ 45 - 70+￿ 40 - 90 approximate Gas filled reservoir

In-Situ Permeability￿ 1.0 - 500+￿ 0.1 - 0.0005￿ <0.1 Migration barrier to Gas (md) L Lenticular reservoirs Capillary Pressure￿ Low￿ Relatively high￿ Moderate 'Tight' Geopressured reservoir Source rock B Blanket Grain Density (g/cm3)￿ 2.65￿ 2.65 - 2.74+ average;￿ Unknown, probably 2.65 - 2.70 reservoirs 'Tight' Geopressured reservoir 2.68 - 2.71 in siltstone Figure WR-18.2 - Generalized schematic cross-section showing general distribution of gas and water in conventional and 'tight' Reservoir Pressure￿ Usually normal-underpressured￿ May be under-overpressured￿ Overpressured (relative) lenticular and 'tight' blanket reservoirs. Note that conventional reservoirs have gas-water contacts while the low-permeability reservoirs do not. A source interval that is still in the active generation stage is needed to charge and 'overpressure' the low- Recovery of Gas in Place 75 - 90￿ ￿ <15 - 50 estimated low for￿ Unknown, probably low￿ (from C. Spencer,1989) (%)￿ individual reservoirs permeability reservoir horizons (after C.W. Spencer, 1989). Wind River Reservation UNCONVENTIONAL PLAY TYPE 13 Page 17 of 18 Wyoming Basin-Center Gas Play Wind River General References Spencer, C., 1989, Review of Characteristics of Low-Permeability Gas Reservoirs in Western United States, AAPG Bulletin, V. 73, No.5, p. 613-629. Anderson, T., and O'Connell, P., 1993, Structural Geology of the Circle Ridge Oilfield, Fremont County, Wyoming, in 1993, WGA Oil and Gas and other Resources of the Wind Steidtmann, J., McGee, L., & Middleton, L., 1983, Laramide Sedimentation, River Basin, Wyoming, Special Symposium 1993, eds., Keefer W., Metzger, W., & Folding, and Faulting in the Southern Wind River Range, Wyoming, in Godwin, L. RMAG, 1983, Rocky Mountain Foreland Basins and Uplifts, ed. Lowell, J., p. 161-179. Burtner, R.L., & Warner, M.A., 1984, Hydrocarbon generation in ￿ lower Cretaceous Mowry and Skull Creek Shales of the Northern Rocky Mountain area in the Permian Tisoncik, D., 1984, Regional Lithostratigraphy of the Phosphoria Formation in the Phosphoria Formation, in 1984, RMAG Hydrocarbon source rocks of the greater Rocky Overthrust Belt of Wyoming, Utah, and Idaho, in RMAG Hydrocarbon source Mountain region, p. 449-467. rocks of the greater Rocky Mountain region, p. 295 - 319.

Dolson, J., Muller, D., Evetts, M.J., & Stein, J.A., 1991, Regional Paleotopographic Trends and Willis, J., and Groshong, Jr., R., 1993, Deformational Style of the Wind River Production, Muddy Sandstone (Lower Cretaceous), Central and Northern Rocky Uplift and Associated Flank Structures, Wyoming, 1993, in 1993, WGA Oil Mountains, ￿ AAPG Bulletin, V.75, No.3, p. 409-435. and Gas and other Resources of the Wind River Basin, Wyoming, Special Symposium 1993, eds., Keefer W., Metzger, W., & Godwin, L. Flores, R. and Keighin, C, 1993, Reservoir Anisotropy and Facies Stratigraphic Framework in the Paleocene Fort Union Formation, Western Wind River Basin, Wyoming, in 1993, 1995 National Assessment of United States Oil and Gas Resources - Results, WGA Oil and Gas and other Resources of the Wind River Basin, Wyoming, Special Methodology, and Supporting Data, USGS Digital Data Series DDS-30, Symposium 1993, eds., Keefer W., Metzger, W., & Godwin, L. Release 2, 1996, eds. Gautier, D., Dolton, G., Takahashi, K, & Varnes, K.

Gries, Robbie; 1983, North-South Compression of the Rocky Mountain Foreland Structures in 1983, RMAG Rocky Mountain Foreland Basins and Uplifts, ed. Lowell, James D.

Gries, Robbie, 1983, Oil and Gas Prospecting Beneath Precambrian of Foreland Thrust Plates in Rocky Mountains, AAPG Bulletin, V. 67, No.1, p. 1-28.

Johnson, R.C., and Rice, D.D., 1993, Variations in Composition and Origins of Gases from Coal Bed and Conventional Reservoirs, Wind River Basin, Wyoming, in 1993, WGA Oil and Gas and other Resources of the Wind River Basin, Wyoming, Special Symposium 1993, eds., Keefer W., Metzger, W., & Godwin, L.

Keefer, W., and Johnson, R., 1993, Stratigraphy and Oil and Gas Resources in Uppermost Cretaceous and Paleocene Rocks, Wind River Reservation, Wyoming, in 1993, WGA Oil and Gas and other Resources of the Wind River Basin, Wyoming, Special Symposium 1993, eds., Keefer W., Metzger, W., & Godwin, L..

Maughan, E.K., 1984, Geological setting and some geochemistry of petroleum source rocks in the Permian Phosphoria Formation in 1984, RMAG Hydrocarbon source rocks of the greater Rocky Mountain region, p. 281-294.

Meissner, F.F., 1984, Cretaceous and Lower Tertiary coals as sources for gas accumulations in the Rocky Mountain area, in RMAG Hydrocarbon source rocks of the greater Rocky Mountain region, p. 401-432.

Nuccio, V.F., 1994, Vitrinite reflectance data for the Paleocene Fort Union and Eocene Wind River Formations, and burial history of drill hole data located in central Wind River Basin, Wyoming, in 1994 U.S.G.S. Technical Report #32.

Peterson, J., 1988, Review: Carbonate Reservoir Facies, Wyoming and parts of Montana, in 1988, RMAG, Occurrence and Petrophysical Properties of Carbonate Reservoirs in the Rocky Mountain Region, p. 75-96.

Phillips, S., 1983, Tectonic Influence on Sedimentation, Waltman Member, Fort Union Formation, Wind River Basin, Wyoming, in RMAG, 1983, Rocky Mountain Foreland Basins and Uplifts, ed. Lowell, J., p. 149-160.

Wind River Reservation REFERENCES Page 18 of 18 Wyoming