Changes

'''By Bruce Hart, Western University, London, Ontario, Canada'''

'''By Bruce Hart, Western University, London, Ontario, Canada'''

[[file:Figure1MancosCommRept.jpg|300px|thumb|{{figure number|1}}Type logs through the Cretaceous section of the San Juan Basin, showing the principle stratigraphic units. Note the interval commonly drilled in the Offshore Mancos Shale play. Modified from Hart<ref name=Hart>Hart, B. S., 2021, Stratigraphy and Hydrocarbon Resources of the San Juan Basin: Lessons for Other Basins, Lessons from Other Basins: The Mountain Geologist, in press</ref>.]]

[[file:Figure1MancosCommRept.jpg|300px|thumb|{{figure number|1}}Type logs through the Cretaceous section of the San Juan Basin, showing the principle stratigraphic units. Note the interval commonly drilled in the Offshore Mancos Shale play. Modified from Hart<ref name=Hart>Hart, B. S., 2021, Stratigraphy and Hydrocarbon Resources of the San Juan Basin: Lessons for Other Basins, Lessons from Other Basins: The Mountain Geologist, in press.</ref>.]]

Sharp reductions in demand for oil and gas dramatically affected drilling in the San Juan Basin of New Mexico and Colorado. This summary focuses on the Mancos Shale play in the period 2017-2020 although other unconventional targets (e.g., tight-gas plays of the Dakota and Mesaverde, CBM from the Fruitland Coal) have been drilled and produced for more than 70 years. [[:file:Figure1MancosCommRept.jpg|Figure 1]] shows a type log through the Cretaceous section of the San Juan Basin.

Sharp reductions in demand for oil and gas dramatically affected drilling in the San Juan Basin of New Mexico and Colorado. This summary focuses on the Mancos Shale play in the period 2017-2020 although other unconventional targets (e.g., tight-gas plays of the Dakota and Mesaverde, CBM from the Fruitland Coal) have been drilled and produced for more than 70 years. [[:file:Figure1MancosCommRept.jpg|Figure 1]] shows a type log through the Cretaceous section of the San Juan Basin.

* The “Offshore Mancos Shale play” targets shales and shaly sandstones, including both low-quality reservoir rocks and Type II-III source rocks. As such, it is best described as a hybrid play.

* The “Offshore Mancos Shale play” targets shales and shaly sandstones, including both low-quality reservoir rocks and Type II-III source rocks. As such, it is best described as a hybrid play.

[[file:Figure3MancosCommRept.jpg|300px|thumb|{{figure number|3}}Oil (green) and gas (red) wells drilled in Mancos pools. A) In the period 2017-2020 (125 wells). B) In 2020 alone (11 wells). Contours show the top Dakota elevation, simplified from Craigg<ref name=Craigg>Craigg, S. D., 2001, Geologic framework of the San Juan Structural Basin of New Mexico, Colorado, Arizona, and Utah, with emphasis on Triassic through Tertiary rocks: US Geological Survey Professional Paper 1420, 70 p.</ref>.]]

[[file:Figure3MancosCommRept.jpg|300px|thumb|{{figure number|3}}Oil (green) and gas (red) wells drilled in Mancos pools. A) In the period 2017-2020 (125 wells). B) In 2020 alone (11 wells). Contours show the top Dakota elevation, simplified from Craigg<ref name=Craigg>Craigg, S. D., 2001, Geologic framework of the San Juan Structural Basin of New Mexico, Colorado, Arizona, and Utah, with emphasis on Triassic through Tertiary rocks: U.S. Geological Survey Professional Paper 1420, 70 p.</ref>.]]

[[:file:Figure2MancosCommRept.jpg|Figure 2]] shows examples of the intervals historically completed as Mancos wells from the Offshore Mancos Shale play using vertical wells. The Mancos is divided into two members, Upper and Lower, separated by an unconformity (Base Niobrara Unconformity, BNU) that formed near the end of the Turonian. Mancos production is almost invariably from the Upper Mancos, from an interval sometimes called El Vado or Niobrara. Unfortunately, some pools that produce from the same stratigraphic level are also called Gallup, although that name is stratigraphically incorrect. Shoreline sandstones of the Gallup sit stratigraphically below the BNU.  

[[:file:Figure2MancosCommRept.jpg|Figure 2]] shows examples of the intervals historically completed as Mancos wells from the Offshore Mancos Shale play using vertical wells. The Mancos is divided into two members, Upper and Lower, separated by an unconformity (Base Niobrara Unconformity, BNU) that formed near the end of the Turonian. Mancos production is almost invariably from the Upper Mancos, from an interval sometimes called El Vado or Niobrara. Unfortunately, some pools that produce from the same stratigraphic level are also called Gallup, although that name is stratigraphically incorrect. Shoreline sandstones of the Gallup sit stratigraphically below the BNU.