Powder river basin
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The Powder River Basin is a sedimentary basin located in northeastern Wyoming and southeastern Montana containing an abundance of fossil fuels ranging from crude oil, natural gas, and coal. The Powder River Basin covers nearly 20,000 square miles and is oriented in a northwest-southeast direction spanning approximately 230 miles long and approximately 100 miles wide. Distinct uplifts such as the Miles City Arch, Black Hills, Laramie Range, and Bighorn Mountains define the boundaries of the basin and most of the production arises from the Cretaceous period. Coal is the primary fossil fuel produced from the Basin as the Powder River Basin is the leading coal producing basin in the United States by producing 43% of the nation’s coal per year. Crude oil and natural gas production figures in the basin have risen in recent years with the onset of horizontal drilling.
The Paleozoic time period includes anything deposited between the Cambrian and the Permian. This period was defined by mostly marine deposition in the shallow sea that covered the area up until the Pennsylvanian period. During the Pennsylvanian a transgression occurred; bringing non-marine sediments into the basin. The reason that there is not much production taken from the rocks in this time period is that erosion destroyed many of the hydrocarbon deposits over time and many of the traps are deep beneath several layers of rock that make it difficult and often uneconomic to pursue these formations. 
The Mesozoic time period includes anything deposited between the Triassic and the Cretaceous. Most of the hydrocarbon production in the region comes from this time period, specifically the Cretaceous. Towards the end of the Jurassic and the beginning of the Cretaceous, the sea experienced several transgression/regression cycles that deposited a high amount of organic material in the basin from both marine and non-marine sources. This is why you see the majority of oil production in the Powder River Basin come from the Upper and Lower Cretaceous formations.
The Tertiary time period was not so much responsible for the creation of hydrocarbon deposits within the basin, but more so for where those deposits are now located. Many tectonic movements during this time caused the locations of deposits to shift. The Tertiary period was primarily defined by folds and faults in the earth’s crust due to plate tectonics. This created the faults we see to the west of the Powder River Basin.
One of the primary geologic risk in the Niobrara Formation is the uncertainty on the natural fractures and faults within the formation. For instance, fracture connectivity with the formation is not currently well known, which creates concerns as fracture connectivity gives indication on the distribution of fluids. Another major geologic risk in the Powder River Basin is the increasing drilling depths required to reach shale formations in the basin. For instance, drilling depths in the Niobrara have increased throughout time and now wells are approaching depths near 12,000 feet per well. Consequently, there is concern with the drilling expertise necessary to successful obtain production at depths this large and the cost associated with drilling deeper wells. Additionally, it is projected that new oil discoveries in the Niobrara Formation will occur in the deepest areas of the basin in overpressured reservoirs creating another geologic risk. The geologic risk brought with finding additional oil in the Niobrara is to find producible sandstone in an overpressured area. 
The productive Niobrara Formation in the basin contains calcareous shale, shaley limestone, and marls as reservoir rocks. According the USGS, reservoir zones in the Niobrara range from 50 to 200 feet in thickness, however, there have been wells drilled in the basin where the zones were near 400 feet. The most prolific benches composed of these reservoir rocks within the Niobrara are the Wolf Mountain, Tow Creek, and Buck Peach benches. Nonetheless, the reservoir rocks in the Niobrara are held to hold unfavorable porosity and permeability due to the fine-grained nature of the reservoir rocks. As a result, production from Niobrara requires hydraulic fracturing to adequately develop the reservoir.
Trap and Seal
The forms of traps within the productive Niobrara formation in the Powder River Basin are classified to be stratigraphic in addition to structural straps. Stratigraphic traps in the Niobrara formation arose from the deposition of reservoir rock sandstones next to shales creating stratigraphic facies change traps. Well Draw, a prominent field producing from the Niobrara formation, is a key example of a stratigraphic facies change trap created in the basin from a facies change from sandstone to shale. Structural traps created in the basin are primarily fault traps created by Laramide deformation. Common seals in Niobrara formation range from shales and siltstones whose low permeability and porosity qualities assist in preventing oil within reservoir rock sandstones from escaping.
Source Rock and Migration
The source rocks in the major producers (namely the Niobara) of the Powder River Basin consist primarily of carbonates that were allowed to form when the sea level was relatively low in the region. Constant transgression and regression of the oceans covering the basin also brought sediment from further inland that was eventually turned into shale. This shale now surrounds the hot spots that are considered to be within the Niobara formation. The hydrocarbon migration of the Niobara is considered to be mostly vertical over time. This is due to faults that run vertically through the shale that lies on top and beneath the formation.
Production of crude oil in the Powder River Basin first began in 1889 near the Salt Creek field. The age of petroleum source rocks in the Powder River Basin range from Tertiary, Upper Cretaceous, Lower Cretaceous, Jurassic, Triassic, Permian, Permian-Pennsylvanian, Pennsylvanian-Mississippian. Oil production from the basin has traditionally been steady throughout time, however, the introduction of horizontal drilling to the basin has caused production to tremendously increase. For instance, 24.6 million barrels of oil were produced from the basin in 2000 and 41.8 million barrels of oil were produced from the basin in 2014. The Powder Basin is still being sought by industry for crude exploration opportunities as the most recent assessment of oil reserves left in the basin conducted in 2006 by the USGS estimated there was approximately 639 million barrels of oil left.
Natural gas has traditionally not been at the forefront of petroleum production in the Powder River Basin, yet the range of yearly natural gas production from the basin has ranged from two hundred to above five hundred billion cubic feet of natural gas in the recent years.  Coalbed natural gas composes most of the natural gas production from the Powder River Basin. For example, Wyoming’s yearly coalbed natural gas production has historically accounted for amounts ranging from 71% to 94% of the Powder River Basin’s yearly total production of natural gas. The USGS’s most recent assessment of undiscovered natural gas in the Powder River Basin administered in 2006 stated there was approximately 16.6 trillion cubic feet of natural gas left. 
Coal is the primary fossil fuel produced from the Powder River Basin due to the extensive coal reserves within the basin. In 2018, the Powder River Basin produced 324 million short tons of coal out of the 756 million short tons of coal produced in the United States. The Fort Union Formation within the basin holds most of the coal in the basin, particularly within the Tongue River member. Coal produced from the Powder River Basin is classified as subbituminous. The Powder River Basin’s coal burns in a range between 8,400 to 8,800 British thermal units per pound. Other common forms of coal such as anthracite and bituminous burn at higher amounts of British thermal units per pound making the Powder River Basin’s subbituminous coal a more economical option. The USGS estimates approximately 975 billion short tons of coal are available for extraction in the basin. 
In addition to petroleum and natural gas deposits, uranium has also been located in the Powder River Basin. Wyoming has been estimated to hold some of the largest uranium deposits in the world, and the planning process for mining projects is well underway in multiple counties in Northeast Wyoming as well as Southwest Wyoming. The mining of uranium can have negative impacts, however, and questions have been raised over the impact on ground water quality, public health, and property values. 
The Powder River Basin has seen increased drilling activity in recent years and operators are using hydraulic fracturing to produce as much as possible from the unconventional play. For instance, companies such as EOG Resources, Noble Energy, Chesapeake, and Devon Energy all have operations in the basin. The drilling depth to the productive Niobrara formation falls in a range between 7,000 and 8,000 feet according to the USGS. The average cost for a well producing from the Niobrara formation for a well-known operator in the Basin, EOG, is roughly $5.9 million dollars. Additionally, EOG uses a lateral length of 9,500 feet for their wells producing from the Niobrara formation.
Despite the attractiveness of the basin, there are factors that can hinder the economics for companies such as the reservoir pressure or sage-grouse restrictions. The Niobrara is characterized as an underpressured reservoir with a pressure gradient of .295 psi/foot. The concern that could potentially arise from the underpressurized characteristic of the reservoir is the chances of stuck drill pipe could be increased due to the pressure differential between the wellbore and the formation. If this occurred, operators would be experiencing additional costs to solve this issue. Another concern for operators is to comply with rules centered around protecting sage-grouse populations as this can affect surface locations for operations or infrastructure. For example, in core population areas for sage-grouse in Wyoming there cannot be any surface occupancy within a .6 mile perimeter of occupied sage-grouse leks. 
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- Coal. (2020, March 12). Retrieved from https://www.wyomingmining.org/minerals/coal/
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- Gordon, M. (2019) Executive Order 2019-3. Retrieved from https://wgfd.wyo.gov/WGFD/media/content/PDF/Habitat/Sage Grouse/Governor-Gordon-Greater-Sage-Grouse-EO-2019-3_August-21-2019_Final-Signed_2.pdf
New petroleum technology revitalizes Powder River Basin oil production, EIA: 
Evolution of sedimentary basins: Powder River Basin, USGS: 
Why the Powder River Basin produces more coal with fewer mines, Market Realist