Wyoming's Oil & Gas Basins

Bighorn Basin Geology

Cross Sections

Geologic Map

Type Log

The Bighorn Basin is an elongate, northwest-trending structural basin in north-central Wyoming. It is approximately 193 km (120 mi) long and up to 145 km (90 mi) wide. In the axis of the basin, Paleozoic, Mesozoic, and Cenozoic rocks are present with a total thickness exceeding 7,620 m (25,000 ft). The basin is bounded on the north and east by the Pryor and Bighorn Mountains, and on the south and west by the Owl Creek, Absaroka, and Beartooth mountains.

The present structural configuration of the Bighorn Basin resulted from the Late Cretaceous through Early Eocene Laramide orogeny (Blackstone, 1963), during which the peripheral mountain uplifts experienced their major growth. The folding and faulting that formed the present oil-producing anticlines in the Bighorn Basin occurred during pulses of compressional stress, mainly oriented northeast-southwest.

Fox and Dolton (1996) defined the types of plays prevalent in the Bighorn Basin and suggested some potential plays for future development as part of a resource assessment of the basin. Both structural and stratigraphic traps occur in Paleozoic and Cretaceous source-rock/reservoir systems in the basin. Structural plays include basin margin subthrusts, basin margin anticlines, deep basin structures, and sub-Absaroka-volcanics. Principal stratigraphic plays include Phosphoria pinchout (up-dip facies change) and Tensleep paleogeography (dune fields versus interdune regions) (Fox and Dolton, 1996). Significant potential plays include basin center/deep gas and coalbed natural gas.

Although most of the basin's production comes from anticlinal or other structural traps, Lawson and Smith (1966) suggested that many of the structurally-controlled traps are influenced by stratigraphic effects, including intraformational variations in permeability and, as in the Bonanza and Nowood fields, incised channels in the Tensleep surface that were later filled with impervious Goose Egg sediments. Later Laramide folding may have been superimposed on or near these primary traps. Pure stratigraphic traps are also productive within the Bighorn Basin. The largest of these is the Cottonwood Creek field in the southeast corner of the basin, a trap resulting from an eastward, updip facies change from Phosphoria carbonate to the impermeable red shale and anhydrite facies of the Goose Egg Formation.

The source of essentially all the oil and gas found in Paleozoic reservoirs in the basin is the dark, phosphatic, fine-grained, marine facies of the Phosphoria Formation (Stone, 1967). Primary migration began immediately after deposition of Triassic sediments and was completed by Early Jurassic time. Hydrocarbons accumulated in regional stratigraphic traps created by up-dip facies changes, pinch-outs, or truncation of the reservoir rocks in the Phosphoria, and irregular truncation of thick Tensleep Sandstone beds prior to the deposition of the impervious Phosphoria/Goose Egg Formation. This situation is especially prevalent east of the area covered by marine carbonate facies of the Phosphoria Formation (Stone, 1967). Oil and gas in some of these stratigraphic traps were later released by fracturing and faulting associated with Laramide folding. During the Laramide orogeny, these hydrocarbons moved into older Paleozoic reservoir rocks and older structures where they were trapped in common pools. The occurrence of a common oil-water contact, in many cases, is attributed to fractures joining the reservoirs. Also, the oil-water contact is often tilted as a result of hydrodynamic flow (Stone, 1967).

Mesozoic formations produce a much lower percentage of the Bighorn Basin’s oil and gas, with the most production coming from the Upper Cretaceous Frontier Formation. Source rocks in the Mesozoic include the Cody, Frontier, Mowry, and Thermopolis black shale units (Stone, 1967).

Production

The Bighorn Basin is primarily an oil-producing basin. Oil was first discovered in the basin in 1904 as a spring on the Bonanza anticline. In 1905, the first producing oil well in the basin was drilled into the Tensleep Sandstone in the Bonanza field. Since these initial discoveries, more than 143 oil fields produce (or have produced) from 60 reservoirs and/or co-mingled reservoirs ranging in age from Cambrian to Paleocene. Seven fields within the Bighorn Basin are in the top 10 cumulative oil-producing fields in Wyoming, with two more fields ranking within the state’s top 25 (WOGCC, 2018). However, oil gas production in the Bighorn Basin has steadily declined since 1978.

Future Development

Despite the decreasing production levels, most fields in the Bighorn Basin still contain a significant quantity of recoverable oil. In response, energy extraction companies are utilizing new and traditional secondary and tertiary recovery techniques to revitalize old fields and to activate fields that were not economically feasible in years past. Future oil production in the Bighorn Basin will heavily rely on these recovery techniques.

Unconventional reservoir plays could also improve oil and gas production in the Bighorn Basin. Many of the same Cretaceous formations exist in the Bighorn Basin that are currently being exploited as unconventional reservoirs in other Wyoming basins. Future exploration for similar unconventional plays, horizontal drilling, and hydraulic fracturing could again make the Bighorn Basin a major player in state oil and gas production.

►References

Blackstone, D.L., Jr., 1963, Development of geologic structures in central Rocky Mountains, in Childs, O.E., and Beebe, B.W., eds., Backbone of the Americas—Tectonic history from pole to pole: Tulsa, Ok., American Association of Petroleum Geologists Memoir, p. 160-179.

Fox, J.E., and Dolton, G.L., 1996, Petroleum geology of the Bighorn Basin, north-central Wyoming and south-central Montana, in Bowen, C.E., Kirkwood, S.C., and Miller, T.S., eds., Resources of the Bighorn Basin: Casper, Wy. , Wyoming Geological Association, 47th annual field conference, Guidebook, p. 19-39.

Lawson, D.E., and Smith, J.R., 1966, Pennsylvanian and Permian influence on Tensleep oil accumulation, Bighorn Basin, Wyoming: American Association of Petroleum Geologists Bulletin, v. 50, no. 10, p. 2,197-2,220.

Stone, D.S, 1967, Theory of Paleozoic oil and gas accumulation in Bighorn Basin, Wyoming: American Association of Petroleum Geologists Bulletin, v. 51, no. 10, p. 2,056—2,114.

WOGCC, 2018, Wyoming Oil and Gas Conservation Commission website, accessed May 15, 2018, at http://wogcc.state.wy.us/legacywogcce.cfm.

Denver Basin Geology

Cross Section (from the Colorado Geological Survey)

Geologic Map

Type Log

The Denver Basin of Wyoming is an asymmetrical Laramide-age basin in the southeastern corner of the state that covers more than 180,000 square km (70,000 square mi) in parts of Colorado, Wyoming, South Dakota, Kansas, and Nebraska. The basin is often termed the Denver-Julesburg Basin, or the Denver-Julesburg-Wattenburg Basin. The bulk of the basin is in Colorado. In Wyoming, the Denver Basin is bounded on the west by the Laramie Range and on the north by the Hartville Uplift.

The Denver Basin has typical foreland basin-style geometry with a north-south trending basin axis. The strata on the western side of the basin dip steeply toward the east, while the strata in the eastern Denver Basin gently slope to the west. The basin is more than 3,962 m (13,000 ft) deep, as defined by the 1.6 billion year-old Precambrian basement. The bulk of the strata preserved in the Denver Basin were deposited during and after Laramide deformation, and are thus Cretaceous age and younger. Surface outcrops in the Denver Basin are generally Tertiary in age.

The Silo field, discovered in 1981 (Sonnenberg, 2011), is the largest field in the basin and the largest horizontally-drilled field in Wyoming. Production in the Silo field is primarily from the Cretaceous Niobrara Formation, which is predominantly fractured chalk (reservoir) encased in tight shales and mudstones (seal). This unconventional reservoir is conducive to horizontal drilling and hydraulic fracturing that significantly enhance production.

Production

Oil and gas was first discovered in the Denver Basin in 1901, and it now includes approximately 1,500 hydrocarbon fields spanning several states (Higley and Cox, 2007). The Denver Basin of Wyoming has 31 named oil and gas fields, 18 of which are not currently producing oil or gas (WSGS oil and gas map). Production has fluctuated through the years, with an increase of more than an order of magnitude from 2009 through 2017 (WOGCC, 2018).

Future Development

Although production efforts in the Denver Basin have historically focused on the Niobrara Formation, operators are beginning to explore other unconventional plays in the basin. Horizontal drilling and hydraulic fracturing have increased recent production from the tight sand formations of the Upper Cretaceous Muddy "J" Sandstone and the Codell Sandstone Member of the Carlile Shale. As drilling techniques and reservoir characterization in the Denver Basin are refined and improved, increased production from unconventional reservoirs is expected to continue.

►References

Higley, DK., and Cox, DO., 2007, Oil and gas exploration and development along the Front Range in the Denver Basin of Colorado, Nebraska, and Wyoming, in Higley, DK., comp., Petroleum systems and assessment of undiscovered oil and gas in the Denver Basin Province, Colorado, Kansas, Nebraska, South Dakota, and Wyoming—USGS Province 39: U.S. Geological Survey Digital Data Series DDS-69-P, chap. 2, 41 p.

Sonnenberg, S.A., 2011, Silo field summary, in Estes-Jackson, J.E., and Anderson, D.S., eds. Revisiting and revitalizing the Niobrara in the central Rockies: Denver, Co., Rocky Mountain Association of Geologists, p. 494—497.

WOGCC, 2018, Wyoming Oil and Gas Conservation Commission website, accessed May 15, 2018, at http://wogcc.state.wy.us/legacywogcce.cfm.

Greater Green River Basin Geology

Cross Sections

Geologic Map

Type Log - Moxa Arch

Type Log - Rock Springs Uplift

The Greater Green River Basin encompasses the southwest portion of Wyoming and extends south into northeastern Utah and northwestern Colorado. The footprint of the basin covers 54,269 km² (20,953 mi²) in Wyoming. The Greater Green River Basin is bounded on the west by the Sevier overthrust belt, on the north by the Wind River Mountain Range, to the east by the Rawlins Uplift and Sierra Madre Mountain Range, and to the south by the Uinta Mountains.

The Greater Green River Basin is an amalgamation of several sub-basins, including the Green River Basin, Great Divide Basin, Washakie Basin, and Sand Wash Basin. These sub-basins were formed during the Late Cretaceous to Early Eocene Laramide orogeny, with the uplift of the Moxa arch, Rock Springs Uplift, Cherokee Ridge arch, and Wamsutter arch. An intermittent record of sedimentation from the Cambrian through present is preserved in the basin, with total compacted sediment fill that can be greater than 9,144 m (30,000 ft) thick.

Many oil and gas fields in the Greater Green River Basin occur in anticlinal traps (Law, 1988). These anticlinal traps are secondary folds on the larger-scale Laramide uplifts. Stratigraphic traps are rare in the basin, with the exception of the Cretaceous formations, such as Patrick Draw field, where an up-dip pinch-out of the Almond Formation traps a significant accumulation of oil (Weimer, 1965, 1966). Structural traps occur in fields such as the giant Jonah gas field, where natural gas is trapped in the Lance Formation sandstones within a fault-bounded wedge (Cluff and Cluff, 2004).

Primary oil production is from the Upper Cretaceous Frontier Formation and Mesaverde Group, followed by the Lower Cretaceous Dakota Sandstone ("Dakota Sandstone" is a formation name borrowed from neighboring states and frequently used in the hydrocarbon industry, but is unofficially recognized in Wyoming). Carbon dioxide and helium production on the LaBarge platform is from the Mississippian Madison Limestone.

Hydrocarbons are also commonly produced from the Pennsylvanian and Permian Tensleep/Weber sandstones. Nearly all formations are known to contain hydrocarbons at one location or another within the Greater Green River Basin.

Hydrocarbon source rocks vary by location within the section and within the basin. The U.S. Geological Survey (USGS Southwestern Wyoming Province Assessment Team, 2005) determined nine regional total petroleum systems in the southwestern Wyoming province (the bulk of which includes the Greater Green River Basin of Wyoming). These nine systems imply source rocks in the Phosphoria Formation, Mowry/Aspen Shale, Hilliard/Baxter Shale, Niobrara Formation, Mesaverde Group, Lewis Shale, Lance and Fort Union formations, and the Wasatch and Green River formations. Excluding the Phosphoria (Permian), Wasatch and Green River formations (Eocene), and Fort Union Formation (Paleocene), all other source rocks are Cretaceous—primarily Upper Cretaceous.

The source rock facies within the Phosphoria Formation are contained within the Meade Peak and Retort members. The Phosphoria was deposited in a sediment-starved, restricted basin on the western edge of the Wyoming shelf (Piper and Link, 2002). Within this complex, the Meade Peak and Retort members were formed in areas favorable for upwelling, high organic productivity, and preservation of organic matter (e.g., Piper and Link, 2002). Total organic content values are as high as 30 weight percent in this organic-rich source rock. High amounts of sulfur suggest original oil composition within the Phosphoria was Type-IIS kerogen, with oil generation beginning during the Late Cretaceous (Johnson, 2005).

The Cretaceous source rocks resulted from relative transgressions and regressions within a foreland basin that was progressively subsiding from the advancing Sevier orogen. These source rocks are all marine shales, some of which were deposited under anoxic conditions that preserved an unusual amount of carbonaceous matter. Of the Cretaceous shales, the Mowry/Aspen Shale has the highest total organic content (Burtner and Warner, 1984) and is primarily responsible for charging the Dakota Sandstone and Frontier Formation reservoirs throughout the Rocky Mountain region (Warner, 1982; Burtner and Warner, 1984), with additional gas locally sourced from the Frontier coals.

Eocene Wasatch and Green River source rocks are lacustrine organic-rich shales and marginal marine and terrestrial coal and carbonaceous mudstones (Roberts, 2005). Lacustrine source rocks contain Type-I and mixed Type-I and Type-Ill kerogen, while the coal and carbonaceous units contain Type-Ill kerogen (Grabowski and Bohacs, 1996; Carroll and Bohacs, 2001). These source rocks are responsible for significant oil shale deposits in the Green River Formation and biogenic gas accumulations (i.e., coalbed natural gas) in both the Wasatch and Green River formations.

Production

The Greater Green River Basin is a mature hydrocarbon province that has been under production since the early 20^th century. There are 303 named fields in the basin, 250 of which have primarily produced natural gas, with some associated oil (WSGS oil and gas map). The basin is home to an accumulation of C0₂ greater than 100 trillion cubic feet on the crest of the Moxa arch, as well as the nation's primary helium reserve. Twelve of Wyoming’s top 100 highest-producing oil fields and more than half of the state’s most productive gas fields are in the Greater Green River Basin. (WOGCC, 2018).

Oil and gas production in the Greater Green River Basin has not declined as much as it has in other Laramide basins throughout Wyoming. This is in part due to the discovery of the giant Jonah gas field, and also due to the success of C0₂-EOR projects in the Lost Soldier and Wertz fields, and the Monell unit in the Patrick Draw field.

Future Development

In general, drilling has decreased in the Greater Green River Basin over the past few years and production has followed this trend. Production of both oil and gas declined since 2010, down from a high of 17.5 million barrels of oil and 1.4 trillion cubic feet of gas (WOGCC, 2018).

However, there are plans to produce oil and gas from many thousand additional wells in the Greater Green River Basin over the coming decades. Production from these future wells should offset the declining production in the Green River Basin.

There are presently five large natural gas projects in various stages of the federal review process in the Greater Green River Basin. The largest two projects are Anadarko’s Blacks Fork project and Jonah Energy’s Normally Pressured Lance project. Combined, these two projects propose to drill 11,000 wells in the western portion of the basin. The primary drilling targets for this Blacks Fork project include the Cretaceous-age sandstones and shales of the Frontier and Dakota formations, while the Normally Pressured Lance project will target the Upper Cretaceous Lance Formation (WSGS oil and gas map).

A handful of small and interesting developments have occurred in the eastern Greater Green River Basin over the past few years. Horizontal drilling and hydraulic fracturing have made for productive natural gas wells in the Paleocene Fort Union Formation in the Washakie Basin and the Mesaverde Group on the far eastern flank of the basin. Improved drilling and production technologies may further increase production from what were historically thought of as tight and unproductive sandstone or shale reservoirs, but are now rather typical unconventional reservoirs.

►References

Burtner, R.L., and Warner, M.A., 1984, Hydrocarbon generation in Lower Cretaceous Mowry and Skull Creek shales of the northern Rocky Mountain areas, in Woodward, J. , Meissner, F.F., and Clayton, J.L., eds., Symposium on hydrocarbon source rocks of the greater Rocky Mountain Region: Denver, Co., Rocky Mountain Association of Geologists, p. 449—467.

Carroll, A.R., and Bohacs, K.M., 2001, Lake-type controls on petroleum source rock potential in nonmarine basins: American Association of Petroleum Geologists Bulletin, v. 85, no. 6, p. 1033-1053.

Cluff, R.M., and Cluff, S.G., 2004, The origin of Jonah field, northern Green River Basin, Wyoming, in Robinson, J.W. , and Shanley, K.W., eds., Jonah field—Case study of a giant tight0gas fluvial reservoir: American Association of Petroleum Geologists Studies in Geology 52 and Rocky Mountain Association of Geologists Guidebook, Chapter 8, p. 127—145.

Grabowski, G.J. , Jr., and Bohacs, K.M., 1996, Controls on compositions and distributions of lacustrine organic-rich rocks of the Green River Formation, Wyoming [abs.]: San Diego, Ca., American Association of Petroleum Geologists and Society of Economic Paleontologists and Mineralogists Annual Meeting, v. 5, p. 55.

Johnson, R.C., 2005, Geologic assessment of undiscovered oil and gas resources in the Phosphoria Total Petroleum System, Southwestern Wyoming Province, Wyoming, Colorado, and Utah, in U.S. Geological Survey Southwestern Wyoming Province Assessment Team, Petroleum systems and geologic assessment of oil and gas in the Southwestern Wyoming Province, Wyoming, Colorado, and Utah: U.S. Geological Survey Digital Data Series DDS-69-D, chap. 4, 46 p.

Law, B.E., 1988, Geologic framework and hydrocarbon plays in the Southwestern Wyoming Basins Province: U.S. Geological Survey Open-File Report 88-450-F, 29 p.

Piper, DZ., and Link, P.K., 2002, An upwelling model for the Phosphoria sea—A Permian, oceanmargin sea in the northwest United States: American Association of Petroleum Geologists Bulletin, v. 86, no. 7, p. 1217—1235.

Roberts, S.B., 2005, Geologic assessment of undiscovered petroleum resources in the Wasatch- Green River Composite Total Petroleum System, Southwestern Wyoming Province, Wyoming, Colorado, and Utah, in U.S. Geological Survey Southwestern Wyoming Province Assessment Team, petroleum systems and geologic assessment of oil and gas in the Southwestern Wyoming Province, Wyoming, Colorado, and Utah: U.S. Geological Survey Digital Data Series DDS-69D, chap. 12, 22 p.

Weimer, R.J., 1965, Stratigraphy and petroleum occurrences, Almond and Lewis formations (Upper Cretaceous), Wamsutter arch, Wyoming: Casper, Wy. , Wyoming Geological Association, 19th annual field conference, Guidebook, p. 65—81.

USGS Southwestern Wyoming Province Assessment Team, 2005, Petroleum systems and geologic assessment of oil and gas in the Southwestern Wyoming Province, Wyoming, Colorado, and Utah: U.S. Geological Survey Digital Data Series DDS-69-D.

Warner, M.A., 1982, Source and time of generation of hydrocarbons in the fossil basin, western Wyoming thrust belt, in Powers, R.B., ed., Geologic studies of the Cordilleran thrust belt: Rocky Mountain Association of Geologists, p. 805—815.

Weimer, R.J., 1966, Time-stratigraphic analysis and petroleum accumulations, Patrick Draw field, Sweetwater County, Wyoming: American Association of Petroleum Geologists Bulletin, v. 50, no. 10, p. 2150-2175.

WOGCC, 2018, Wyoming Oil and Gas Conservation Commission website, accessed May 15, 2018, at http://wogcc.state.wy.us/legacywogcce.cfm.

Hanna Basin Geology

Cross Section

Geologic Map

Type Log

The Hanna Basin is a small yet anomalously deep (9,144 m, 30,000 ft) intermontaine Laramide-style basin, approximately 64 km (40 mi) east-west and 40 km (25 mi) north-south. The basin is bounded to the north by the Shirley and Seminoe mountains, to the east by Simpson Ridge, to the south by the Medicine Bow Mountains and Park Range, and to the west by the Rawlins Uplift.

The structural development of the Hanna Basin occurred in multiple stages. The Hanna Basin was first isolated from the Greater Green River Basin by the uplift of the Shirley and Granite mountains during the early Paleocene, followed by middle-Paleocene growth of the Sweetwater Uplift. The Medicine Bow Mountains and Rawlins Uplift occurred during the late Paleocene. The Cambrian-through Jurassic-age sedimentary strata that accumulated before the structural development of the Hanna Basin are less than 762 m (2,500 ft) thick.

During the Laramide orogeny, the Hanna Basin was isolated from the surrounding basins and became a closed drainage. This structural configuration resulted in a thick succession of Upper Cretaceous to Lower Paleogene fluvial and lacustrine sedimentary deposits. These fluvial and lacustrine strata account for the bulk of the strata in the basin center, and can be up to 5,791 m (19,000 ft) thick.

Production

Dyman and Condon (2005) define the Hanna—Mesaverde coalbed gas total petroleum system in the Hanna Basin, as including portions of the Mesaverde (Almond), Medicine Bow, Ferris, and Hanna formations. Two coalbed natural gas (CBNG) pilot projects in the basin, established by 2005, have produced very little gas from this petroleum system. The Seminoe Road CBNG pilot project contained 16 wells that produced 1,400 cubic feet of gas per day; the Hanna Draw CBNG pilot project had nine wells that averaged less than 1,000 cubic feet of gas per day (Dyman and Condon, 2005).

Conventional oil and gas exploration occurred in the Hanna Basin throughout the 20th century. There are currently 18 named fields in the Hanna Basin, eight of which are abandoned (WSGS oil and gas map). The most productive oil field, Big Medicine Bow field, produces from the Cloverly (Dakota) Formation, Sundance Formation, and Tensleep Sandstone (WOGCC, 2017). The most productive gas field, Separation Flats field, produced from the Muddy Sandstone but is no longer active. The Hanna Basin has not been extensively explored for undiscovered petroleum accumulations, and there are potential conventional and unconventional undiscovered accumulations (Dyman and Condon, 2007).

Coal mining has been active in the Hanna Basin since 1868 (Flores and others, 1999). These mines operated at the town site of Carbon, Wyoming, until 1900, when mining operations moved to the town of Hanna after the railroad was rerouted. Most of the coal extraction in the Hanna as well as Carbon basins (which is separated from the Hanna Basin by the northeast-southwest trending Saddleback Hills anticline) has been from the Hanna coal field (Pierce, 1996). Coal is primarily mined from the Upper Cretaceous and Paleocene Ferris Formation, as well as the Paleocene Hanna Formation.

Future Development

Because of the anomalous structure of the Hanna Basin relative to other Laramide basins (that is, it is a small but very deep basin), exploration targets are limited to the flanks of the basin— the basin center is considered too deep for most exploration. There has been very little exploration in the basin over the past few years, mostly limited to CBNG projects. There are a few confidential Cloverly (Dakota) Formation wells on the western flank of the Hanna Basin with as-yet unknown results. There are no proposed drilling projects on federal lands in the Hanna Basin. Currently, the Hanna Basin is not expected to experience much of an increase in oil and gas production unless CBNG again becomes an economic resource.

►References

Dyman, T.S., and Condon, S.M., 2007, 2005 geologic assessment of undiscovered oil and gas resources, Hanna, Laramie, and Shirley basins Province, Wyoming and Colorado, in U.S. Geological Survey Hanna, Laramie, and Shirley Basins Province Assessment Team, Petroleum systems and geologic assessment of undiscovered oil and gas, Hanna, Laramie, and Shirley basins Province, Wyoming and Colorado: U.S. Geological Survey Digital Data Series DDS-69-K, chap. 2, 62 p.

Flores, R.M., Cavaroc, V.V., Jr., and Bader, L.R., 1999, Ferris and Hanna coal in the Hanna and Carbon basins, Wyoming—A synthesis: U.S. Geological Survey Professional Paper 1625-A, chap. HS, 49 p.

Pierce, B.S., 1996, Quality and petrographic characteristics of Paleocene coals from the Hanna Basin, Wyoming: Jackson, Wy., 12th Annual Meeting of the Society of Organic Petrology, Organic Geochemistry, v. 24, no. 2, p. 181-187.

WOGCC, 2018, Wyoming Oil and Gas Conservation Commission website, accessed May 15, 2018, at http://wogcc.state.wy.us/legacywogcce.cfm.

Laramie Basin Geology

1:24,000-scale bedrock geologic maps

• Best Ranch
• Centennial
• Dale Creek
• Howell
• Johnson Ranch
• Laramie
• Pilot Hill
• Red Buttes
• Sherman Mountains West

1:100,000-scale bedrock geologic maps

• Geologic Map of the Laramie Quadrangle

The Laramie Basin, in southeast Wyoming, is a complexly downfolded Laramide basin. It trends north-south and is approximately 80 km (50 mi) long by 50 km (31 mi) wide. The Laramie Basin is bounded by the Medicine Bow Mountains on the west, the Hanna Basin on the northwest, the Shirley Mountains on the north, and the Laramie Mountains on the east.

Overthrust Belt Geology

Cross Sections

The Overthrust Belt is a zone of highly deformed rock layers stretching from northern Alaska to Mexico. The portion of the Overthrust Belt in Wyoming that has been the target of oil and gas exploration efforts is more than 160 km (100 mi) wide and 320 km (200 mi) long. It is bounded to the north by Jackson Hole, Wyoming, to the east by the Darby and Prospect faults, and to the south by the Uinta Uplift.

The Overthrust Belt is not part of the Laramide Basin system, but was instead created by the Cretaceous-age Sevier orogeny approximately 150 to 55 million years ago. The Sevier orogeny was a shortening event that resulted in "thin-skinned" thrusting, or generally north-south oriented thrust faults that do not involve the Precambrian basement rocks.

Often termed the Thrust Belt or Sevier Belt, the Overthrust Belt contains a series of anticlinal traps that can store hydrocarbons. These potential traps can be seen on cross sections of the Overthrust Belt. The complexity of the Overthrust Belt's geology, including highly folded and faulted strata, has contributed, and continues to contribute, to the difficulty of exploring for oil and gas in this area.

The Jurassic Nugget Sandstone and the Mississippian Madison Limestone have been the most prolific oil and gas producing formations in Wyoming's Overthrust Belt. From 1978 through 2017, more than 167 million barrels of crude and nearly 11 trillion cubic feet of gas were produced from these two formations (WOGCC, 2018).

Other, mostly gas-producing, formations in the Overthrust Belt include the Ordovician Big Horn Dolomite; Pennsylvanian Amsden Formation; Permian Phosphoria Formation and Weber Sandstone; Triassic Thaynes Limestone; Jurassic Twin Creek Limestone; Cretaceous Baxter, Mesaverde, Muddy, and Bear River formations; and Eocene Almy Formation.

The main source rock in the Overthrust Belt is presumed to be the Cretaceous Mowry Shale. The Permian Phosphoria Formation and other Cretaceous organic-rich formations, such as the Bear River and Frontier formations, may also be minor sources of oil and gas in the region (USGS Wyoming Thrust Belt Province Assessment Team, 2003).

Production

Exploration began in the late 1800s and early 1900s in the Overthrust Belt region, primarily in shallow fields associated with oil seeps. These small fields were unsuccessful. Despite the discovery of the large La Barge and Dry Piney fields in the mid-1900s in the transition zone between the Greater Green River Basin and the Overthrust Belt, intensive exploratory efforts did not commence until the discovery of several fields during the mid-1970s (Ver Ploeg, 1979).

Twenty-four fields within the Overthrust Belt have been reported as having produced oil or natural gas (WSGS oil and gas map). The bulk of the gas production, which is significant, is from the Fogarty Creek, Painted Reservoir East, Lake Ridge, and Whitney Canyon-Carter Creek fields (WOGCC, 2018).

Future Development

Although there have been rumors of an emerging Phosphoria Formation horizontal play in the Overthrust Belt, there are no data on the WOGCC (2018) website validating this rumor. No productive wells have been drilled in the area since 2012, and at this point, there appears to be no new Overthrust Belt oil or gas projects on the horizon.

►References

USGS Wyoming Thrust Belt Province Assessment Team, 2003, Assessment of Undiscovered Oil and Gas Resources of the Wyoming Thrust Belt Province: U.S. Geological Survey World Energy Assessment Project Fact Sheet.

Ver Ploeg, A.J., 1979, The Overthrust Belt—An overview of an important new oil and gas provinceThe Overthrust Belt—An overview of an important new oil and gas province: Geological Survey of Wyoming [Wyoming State Geological Survey] Public Information Circular no. 11, 15 p.

WOGCC, 2018, Wyoming Oil and Gas Conservation Commission website, accessed May 15, 2018, at http://wogcc.state.wy.us/legacywogcce.cfm.

Powder River Basin Geology

Cross Section

Geologic Map

Type Log

The Powder River Basin area encompasses the Powder River structural basin and Powder River energy basin. The structural basin is an asymmetric trough in southeastern Montana and northeastern Wyoming that trends north-south for approximately 401 km (250 mi) and is 161 km (100 mi) wide. It is bounded to the south by the Casper Arch, Laramie Mountains, and Hartville Uplift; to the west by the Bighorn Mountains; to the north by the Miles City arch in Montana; and to the east by the Black Hills. The Powder River energy basin is loosely defined by the Cretaceous–Tertiary boundary observed in outcrops.

Formations in the Powder River Basin have near-vertical to overturned dips along the western margin and gentle sub-horizontal (basinward) dips along the eastern margin. Structural deformation began in the Powder River Basin region during deposition of the Upper Cretaceous (Maastrichtian) Lewis Shale and ended during deposition of the Eocene Wasatch Formation (Curry, 1971), resulting in structural relief greater than 7,620 m (25,000 ft) (Blackstone, 1981). Nearly 2,438 m (8,000 ft) of syn-Laramide sedimentary rocks are preserved within the Powder River Basin (Curry, 1971).

Hydrocarbon fields within the Powder River Basin generally occur as stratigraphic traps or in basin-bounding anticlinal structures, and are generally classified as producing from Paleozoic or Mesozoic strata. The Tensleep Sandstone and Minnelusa Formation are the major Paleozoic oil producers. According to Dolton and others (1990), the Tensleep primarily produces from structural (anticlinal) traps and the Minnelusa produces from both structural and stratigraphic traps.

The hydrocarbon source rocks that likely charged the Tensleep and Minnelusa reservoirs were Permian shales in western Wyoming. Dolton and others (1990) argue that the hydrocarbons were generated by Jurassic time, migrated east, and were trapped until the Laramide orogeny.

Subsequent uplift allowed some hydrocarbons to escape, while some remained in the Tensleep and Minnelusa reservoirs. In the eastern parts of the basin, lower Minnelusa reservoirs may have been locally sourced from interbedded black shales (Clayton and Ryder, 1984).

Formations deposited during the Cretaceous represent the other major hydrocarbon reservoirs in the Powder River Basin. These include the Muddy Sandstone (eastern equivalent of the Newcastle Sandstone), Wall Creek Sandstone Member of the Frontier Formation, and Turner Sandstone Member of the Carlile Shale. Historically less-productive Cretaceous-age reservoirs such as the Lakota Formation, Fall River (Dakota) Sandstone, Mowry Shale, Frontier Formation, Niobrara Formation, Shannon and Sussex sandstone members of the Cody Shale, Teapot and Parkman sandstone members of the Mesaverde Formation, and the Teckla Sandstone Member of the Lewis Shale are now the main focus of unconventional resource exploration and production in the Powder River Basin.

The source rock for most of the Upper Cretaceous hydrocarbon reservoirs is the Mowry Shale, with significant contributions from the Niobrara Formation and Carlile Shale (Momper and Williams, 1984; Dolton and others, 1990). Hydrocarbons were generated in the deeper western part of the basin and migrated up-dip toward the east into the Cretaceous reservoirs. Estimates suggest nearly 12 billion barrels of oil were generated in the Mowry Shale (Momper and Williams, 1984).

Production

Development of the Powder River Basin as a hydrocarbon-producing basin followed slowly behind development in the other Laramide basins. The first producing oil well in the basin was drilled in 1889 north of Salt Creek field, which is still the most productive oil field in Wyoming. Numerous fields were discovered over the following years, but development was not steady until crude prices and transportation stabilized (Hughes, 1983).

The Powder River Basin was historically an oil-producing basin. Gas occurrences were rare and were usually gas caps associated with oil reservoirs. However, coalbed natural gas (CBNG) development in the late 1990s and 2000s changed the Powder River Basin into a significant natural gas-producing region. At its peak in 2009, the Powder River Basin produced more than 584 billion cubic feet of natural gas (WOGCC, 2018). Natural gas production has been declining in the Powder River Basin since 2009, largely due to low gas prices, depleted CBNG reservoirs, and competition from large unconventional gas plays.

Oil production in the Powder River Basin has fluctuated through several boom and bust cycles. In 2010, however, oil production in the basin started increasing dramatically, and has since been reaching levels not seen since the late 1980s (WOGCC, 2018).

Future Development

Lengthy horizontal laterals, multi-lateral completions, and multi-stage hydraulic fracturing are now allowing operators to produce large amounts of oil from previously-uneconomic tight sands and shales. Based on the substantial number of new wells completed and new applications for permits-to-drill within the basin, this upswing in oil production is expected to continue despite low-to-moderate oil prices.

Large oil and gas developments on federal land in Converse and Campbell counties have taken advantage of these technological advancements. Operators in the Greater Crossbow and Converse County developments are expected to drill nearly 6,500 wells—the majority of which will be horizontal—that target stacked, unconventional Upper Cretaceous reservoirs (WSGS oil and gas map).

►References

Blackstone, D.L., Jr., 1981, Compression as an agent in deformation of the east-central flank of the Bighorn Mountains, Sheridan and Johnson Counties, Wyoming: Contributions to Geology, v.19, no. 2, p. 105-122.

Clayton, J.L., and Ryder, R.T., 1984, Organic geochemistry of black shales and oils in the Minnelusa Formation (Permian and Pennsylvanian), Powder River Basin, Wyoming, in Woodward, J. , Meissner, F.F., and Clayton, JL., eds., Hydrocarbon source rocks of the greater Rocky Mountain region: Denver, Co., Rocky Mountain Association of Geologists, p. 231-244.

Curry, W.H., Ill, 1971, Laramide structural history of the Powder River Basin, Wyoming: Casper, Wy., Wyoming Geological Association, 23rd annual field conference, Guidebook, p. 49-60.

Dolton, G.L., Fox, J.E., and Clayton, J.L., 1990, Petroleum geology of the Powder River Basin, Wyoming and Montana: U.S. Geological Survey Open-File Report 88-450-1), 64 p.

Hughes, L., 1983, Case histories of an electromagnetic method for petroleum exploration: Prepared by Zonge Engineering and Research Organization, Inc., Tucson, Ariz., 332 p.

Momper, J.A., and Williams, J.A., 1984, Geochemical exploration in the Powder River Basin, in Demaison, G., and Murris, R.J., eds., Petroleum geochemistry and basin evaluation: Tulsa, Okla., American Association of Petroleum Geologists Memoir 35, p. 181-191

WOGCC, 2018, Wyoming Oil and Gas Conservation Commission website, accessed May 15, 2018, at http://wogcc.state.wy.us/legacywogcce.cfm.

Wind River Basin Geology

Cross Sections

Geologic Map

Type Log

The Wind River Basin, in central Wyoming, is an east-west elongate structural basin of typical Laramide style, 115 km (71 mi) wide by 300 km (186 mi) long. The primary basin axis trends northwest-southeast, and is asymmetrically located near the northern basin margin. The basin is bounded by the Wind River Mountain Range on the west, the Owl Creek Mountains on the north, the Casper Arch to the east, and the Granite Mountains to the south.

Significant deformation occurred in the Wind River Basin during the Laramide orogeny that resulted in a basin center greater than 7,620 m (25,000 ft) deep, beds dipping 10-20 degrees toward the basin center on the south and western margins, and near-vertical to overturned strata on the north and eastern margins (Keefer, 1969). A thick succession of undeformed post-Laramide basin-fill strata was deposited unconformably on the pre-Laramide (pre-Eocene) rocks.

In the Wind River Basin, hydrocarbon traps typically consist of structural features such as domes, anticlines, or faulted anticlines (Keefer, 1969) situated on the basin margins in rocks deposited previous to or coincident with Laramide-age faulting. Other types of structural traps include anticlines or domes near the basin axis, generally in the north and northeast, as well as traps beneath the basin-bounding thrust faults, or sub-thrust plays (Fox and Dolton, 1996).

Some purely stratigraphic traps are also found in the Wind River Basin. The most frequent stratigraphic traps are lateral up-dip (to the east) facies changes in the Phosphoria, Park City, and Goose Egg formations. Others include sandstone pinch-outs in the sandstone reservoirs of the Frontier Formation, Mesaverde Group, and Muddy Sandstone, as well as vertical and lateral cementation variations in Tensleep Sandstone reservoirs. In some cases, structural traps are enhanced by the effects of stratigraphic-trapping. For example, oil and natural gas in Morrison Formation sands are held by a combination structural-stratigraphic trap on the nose of a domal structure in the Poison Spider West field (Gouger, 1989).

The Tensleep Sandstone and Phosphoria and Park City formations comprise the primary reservoir rocks in the basin. The bulk of the hydrocarbons in these formations were sourced from the black shales of the Mead Peak and Retort members of the Phosphoria Formation in western Wyoming and eastern Idaho (Sheldon, 1967; Stone, 1967; Kirschbaum and others, 2007). Migration began soon after generation, and may have been associated with Sevier orogenesis. Hydrocarbons moved up-dip, likely via the porous and permeable Tensleep Sandstone, into the area that is now the Wind River Basin and were trapped by the overlying impermeable Goose Egg Formation (Stone, 1967; Kirschbaum and others, 2007). Laramide faulting and folding was responsible for the subsequent rearrangement of the hydrocarbons into their present day structural and stratigraphic traps. Phosphoria-sourced hydrocarbons are commonly high in sulfur, exhibit high American Petroleum Institute (API) gravities, and are Type-IIS kerogen (Kirschbaum and others, 2007).

Production

Oil production in the Wind River Basin and Wyoming began with the completion of the Mike Murphy #1 well in 1884, just five years after America's first commercial oil well, the Drake well, was drilled. Mike Murphy #1, completed in the Chugwater Group to a depth of 91 m (300 feet) (Mullen, 1989; De Bruin, 2012), was the discovery well for the Dallas (or Dallas Dome) field in the southwestern Wind River Basin. The basin contains the first oil well drilled in Wyoming (Mike Murphy #1), the first logged well in Wyoming (Atlantic Richfield Company Muskrat 2C, September 1936), and the deepest completed well in the Rocky Mountain region (Burlington Resources Big Horn 1-5, completed between 23,758 and 23,902 feet in the Madison Limestone, Madden field).

Of the 118 named fields in the Wind River Basin, 63 primarily produce oil and 55 produce natural gas from reservoirs ranging in age from Mississippian to Eocene in age (WSGS oil and gas map). Additionally, a handful of these fields produce condensate liquids, which are reported as oil by the Wyoming Oil and Gas Conservation Commission. Oil production in the Wind River Basin declined from 1978 through 1995, held steady from 1995 until 2010 at near 4 million barrels per year followed by a slight increase in production before decreasing again to 4 million barrels per year (WOGCC, 2018). Natural gas production in the basin generally increased through 2005, and has been decreasing since 2009 (WOGCC, 2018).

The decline in oil production in the Wind River Basin has been offset recently with the use of efficient secondary and tertiary production techniques like those employed at the current CO₂-EOR project at Beaver Creek field. Although it is possible that small undiscovered petroleum accumulations may exist in the basin (Fox and Dolton, 1996), as with most hydrocarbon fields throughout Wyoming, it is more likely that any future increases in production will be the result of improved recovery methods.

Future Development

That said, the Moneta Divide project, proposed by Aethon Energy and Burlington Resources, may be a game changer. Although still in the federal review process, the Moneta Divide project, near the large Madden gas field in the northeastern Wind River Basin, plans to drill 4,250 wells and produce oil and gas from the Paleocene (Fort Union Formation), Cretaceous (Lance, Mesaverde, Cody, and Frontier formations), and the Mississippian (Madison Limestone) (WSGS oil and gas map). An environmental impact statement is currently being developed for this project, and a draft is scheduled for release mid-2018.

►References

De Bruin, R.H., 2012, Oil and gas map of Wyoming: Wyoming State Geological Survey Map Series MS-55, scale 1:500,000.

Fox, J.E., and Dolton, G.L., 1996, Wind River Basin Province (035), in Gautier, D.L., Dolton, G.L., Takashashi, K.I., and Varnes, K.L., eds., 1995 National assessment of United States oil and gas resources—Results, methodology, and supporting data: U.S. Geological Survey Digital Data Series DDS-30, release 2, 21 p.

Gouger, B.l., 1989, Poison spider west, in Cardinal, D.F., Miller, T., Stewart, W.W., and Trotter, J.F., eds., Wyoming oil and gas fields symposium Bighorn and Wind River basins: Casper, Wy. , Wyoming Geological Association, p. 380-383.

Johnson, R.c., Finn, T.M., Kirschbaum, M.A., Roberts, s.B., Roberts, L.N.R., cook, T., and Taylor, D.J., 2007, The Cretaceous-Lower Tertiary Composite Total Petroleum System, Wind River Basin, Wyoming, in U.S. Geological Survey Wind River Basin Province Assessment Team, Petroleum systems and geologic assessment of oil and gas in the Wind River Basin Province, Wyoming: U.S. Geological Survey Digital Data Series DDS-69-J, chap. 4, 96 p.

Keefer, W.R., 1969, Geology of petroleum in Wind River Basin, central Wyoming: American Association of Petroleum Geologists Bulletin, v. 53, no. 9, p. 1,839-1,865.

Kirschbaum, M.A., Lillis, P.G., and Roberts, L.N.R., 2007, Geologic assessment of undiscovered oil and gas resources in the Phosphoria Total Petroleum System of the Wind River Basin Province, in U.S. Geological Survey Wind River Basin Province Assessment Team, Petroleum systems and geologic assessment of oil and gas in the Wind River Basin Province, Wyoming: U.S. Geological Survey Digital Data Series DDS-69-J, chap. 3, 27 p.

Mullen, C., 1989, Dallas, in Cardinal, D.F., Miller, T., Stewart, W.W., and Trotter, J.F., eds., Wyoming oil and gas fields symposium Bighorn and Wind River basins: Casper, Wy. , Wyoming Geological Association, p. 114-116.

Sheldon, R.P., 1967, Long-distance migration of oil in Wyoming: Mountain Geologist, v. 4, no. 2, p. 53-65.

Stone, D.S, 1967, Theory of Paleozoic oil and gas accumulation in Bighorn Basin, Wyoming: American Association of Petroleum Geologists Bulletin, v. 51, no. 10, p. 2,056-2,114.

WOGCC, 2018, Wyoming Oil and Gas Conservation Commission website, accessed May 15, 2018, at http://wogcc.state.wy.us/legacywogcce.cfm.