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'''By Zachary Hollon, Workhorse Geologic LLC, USA'''

'''By Zachary Hollon, Workhorse Geologic LLC, USA'''

The Lower-Upper Cretaceous, Albian-Cenomanian-aged Mowry Shale in the Powder River Basin of northeastern Wyoming and southeastern Montana (Figures 1 and 2) is a siliceous, organic-rich, dark-gray to black marine [[mudstone]] interbedded with bentonite, sandstone, and silt.<ref>Burtner, R., and M. Warner, 1984, Hydrocarbon generation in Lower Cretaceous Mowry and Skull Creek shales of the northern Rocky Mountain area: Hydrocarbon Source Rocks of the Greater Rocky Mountain Region, Rocky Mountain Association Geologists.</ref><ref>Davis, H. R., C. Byers, and L. Pratt, 1989, Depositional mechanisms and organic matter in Mowry Shale (Cretaceous), Wyoming: AAPG Bulletin, vol. 9, p. 1103–1116.</ref> (Nixon, 1973). Radiolaria tests, Fish scales, fish teeth, fish bones, fecal pellets, inoceramus debris, and ammonites are found in the bedding planes and silt-laminae of the Mowry Shale throughout Wyoming<ref>Anderson, A., and B. Kowallis, 2005, Storm deposited fish debris in the Cretaceous Mowry Shale near Vernal, Utah: Utah Geological Association Publication 33, p. 125–130.</ref> (Davis, 1970). Calcareous cone-in-cone concretions are seen in core and outcrop<ref>Hollon, Z.G., 2014, Elemental chemostratigraphy and reservoir properties of the Mowry Shale in the Bighorn and Powder River basins, Wyoming, USA: MS thesis, Colorado School of Mines, 156 p.</ref>. Numerous bentonite beds up to 3 ft thick in the Mowry Shale allow for the precise recognition of time equivalent strata over vast areas (Nixon, 1973). In outcrop, the Mowry Shale has a distinct profile and weathers to a dark to light gray, is hard, and often has large jointing sets. The Mowry Shale is ranges in thickness from 150 to 250 ft and is a significant source rock for the Cretaceous reservoirs in the Powder River Basin.

The Lower-Upper Cretaceous, Albian-Cenomanian-aged Mowry Shale in the Powder River Basin of northeastern Wyoming and southeastern Montana (Figures 1 and 2) is a siliceous, organic-rich, dark-gray to black marine [[mudstone]] interbedded with bentonite, sandstone, and silt.<ref>Burtner, R., and M. Warner, 1984, Hydrocarbon generation in Lower Cretaceous Mowry and Skull Creek shales of the northern Rocky Mountain area: Hydrocarbon Source Rocks of the Greater Rocky Mountain Region, Rocky Mountain Association Geologists.</ref><ref>Davis, H. R., C. Byers, and L. Pratt, 1989, Depositional mechanisms and organic matter in Mowry Shale (Cretaceous), Wyoming: AAPG Bulletin, vol. 9, p. 1103–1116.</ref> <ref name=Nxon>Nixon, R. P., 1973, Oil Source Beds in Cretaceous Mowry Shale of Northwestern Interior United States: AAPG Bulletin, vol. 57, no. 1, p. 136–161</ref>. Radiolaria tests, Fish scales, fish teeth, fish bones, fecal pellets, inoceramus debris, and ammonites are found in the bedding planes and silt-laminae of the Mowry Shale throughout Wyoming<ref>Anderson, A., and B. Kowallis, 2005, Storm deposited fish debris in the Cretaceous Mowry Shale near Vernal, Utah: Utah Geological Association Publication 33, p. 125–130.</ref> (Davis, 1970). Calcareous cone-in-cone concretions are seen in core and outcrop<ref>Hollon, Z.G., 2014, Elemental chemostratigraphy and reservoir properties of the Mowry Shale in the Bighorn and Powder River basins, Wyoming, USA: MS thesis, Colorado School of Mines, 156 p.</ref>. Numerous bentonite beds up to 3 ft thick in the Mowry Shale allow for the precise recognition of time equivalent strata over vast areas<ref name=Nxon />. In outcrop, the Mowry Shale has a distinct profile and weathers to a dark to light gray, is hard, and often has large jointing sets. The Mowry Shale is ranges in thickness from 150 to 250 ft and is a significant source rock for the Cretaceous reservoirs in the Powder River Basin.

Exploration and production from the Mowry Shale has been periodic and slow. As the writing of this, there are 47 completed horizontal wells in the Mowry, 17 of which have been drilled since 2018, and most of the wells are south of the Belle Fourche Arch in Campbell and Converse Counties. The 2006-2015 one-mile laterals rarely made commercial wells, plagued by drilling and completion issues from the thick bentonites that are found throughout the Mowry. EOG’s return to the Mowry Shale in 2018 with modern slickwater completions designs and two-mile laterals proved the Mowry to be a commercial oil play in their core acreage, renewing interest from basin operators. In 2019, the Mowry had its largest production, producing ~986,000 BO, ~9.4 BCF, and ~1,800,000 BW. In 2020, the Mowry production decreased slightly, producing ~960,000 BO, ~8.5 BCF, and ~1,200,000 BW (Figure 3) (WOGCC, 2021).

Exploration and production from the Mowry Shale has been periodic and slow. As the writing of this, there are 47 completed horizontal wells in the Mowry, 17 of which have been drilled since 2018, and most of the wells are south of the Belle Fourche Arch in Campbell and Converse Counties. The 2006-2015 one-mile laterals rarely made commercial wells, plagued by drilling and completion issues from the thick bentonites that are found throughout the Mowry. EOG’s return to the Mowry Shale in 2018 with modern slickwater completions designs and two-mile laterals proved the Mowry to be a commercial oil play in their core acreage, renewing interest from basin operators. In 2019, the Mowry had its largest production, producing ~986,000 BO, ~9.4 BCF, and ~1,800,000 BW. In 2020, the Mowry production decreased slightly, producing ~960,000 BO, ~8.5 BCF, and ~1,200,000 BW (Figure 3) (WOGCC, 2021).

 

Wyoming Oil and Gas Conservation Commission - http://pipeline.wyo.gov/legacywogcce.cfm

Wyoming Oil and Gas Conservation Commission - http://pipeline.wyo.gov/legacywogcce.cfm