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However, the Niobrara Formation includes not only good organic-rich mudstones, but also interbedded organic-lean carbonates, typically referred to as the Niobrara A, B, and C carbonates, with the B carbonate being the primary production zone.

However, the Niobrara Formation includes not only good organic-rich mudstones, but also interbedded organic-lean carbonates, typically referred to as the Niobrara A, B, and C carbonates, with the B carbonate being the primary production zone.

Data from core chips of the Golden Buckeye Petroleum 2-Gill Land Associates well demonstrate this vastly different TOC content (Tanck, 1997) ([[:File:M97Ch1.2FG8.jpg|Figure 8]]). This well flowed 20.7 m3 (130 bbl/day) of oil and 7220.8 m3 (255 mcf/day) of gas, with only 1.11 m3 (7 bbl/day) of water from the Niobrara B interval. The GOR is reported at 308.1 m3/m3 (1730 scf/bbl). The thesis by Tanck (1997) did not include carbonate carbon data, although calcite content is reported to be 84% at 2066.2 m (6779 ft). The productive Niobrara B is found in the 2054.3 to 2065.0 m (6740 to 6775 ft) interval, where oil crossover exists ([[:File:M97Ch1.2FG8.jpg|Figure 8]]). Oil saturations range from 63 to 80% of pore volume, with porosities of approximately 5 to 6% in this interval (Tanck, 1997). A deeper zone at 2075.7 to 2080.3 m (6810–6825 ft) has similarly high oil saturations, but much lower porosities in the 3 to 4% range (Tanck, 1997).

Data from core chips of the Golden Buckeye Petroleum 2-Gill Land Associates well demonstrate this vastly different TOC content<ref name=Tnck>Tanck, G. S., 1997, Distribution and origin of organic carbon in the Upper Cretaceous Niobrara Formation and Sharon Springs Member of the Pierre Shale, Western Interior, United States: Ph.D. thesis, University of Arizona, Tuscon, Arizona, 411 p.</ref> ([[:File:M97Ch1.2FG8.jpg|Figure 8]]). This well flowed 20.7 m3 (130 bbl/day) of oil and 7220.8 m3 (255 mcf/day) of gas, with only 1.11 m3 (7 bbl/day) of water from the Niobrara B interval. The GOR is reported at 308.1 m3/m3 (1730 scf/bbl). The thesis by Tanck<ref name=Tnck /> did not include carbonate carbon data, although calcite content is reported to be 84% at 2066.2 m (6779 ft). The productive Niobrara B is found in the 2054.3 to 2065.0 m (6740 to 6775 ft) interval, where oil crossover exists ([[:File:M97Ch1.2FG8.jpg|Figure 8]]). Oil saturations range from 63 to 80% of pore volume, with porosities of approximately 5 to 6% in this interval.<ref name=Tnck /> A deeper zone at 2075.7 to 2080.3 m (6810–6825 ft) has similarly high oil saturations, but much lower porosities in the 3 to 4% range.<ref name=Tnck />

 

The shale intervals are more organic rich and have higher oil contents indicative of source rocks that have generated hydrocarbons. In general, however, the higher the TOC, the lower is the oil crossover. Porosities are also lower in the shale, typically in the range of 2 to 3%.<ref name=Tnck />

The % Roe data from Tmax suggest a consistent trend over the 240 ft (73 m) interval reported. The Tmax increases from about 435 to 450degC (815 to 842degF) or 0.67 to 0.95% Roe. This is indicative of a very high paleogeothermal gradient, suggesting a very high heat flux. Zones with low Tmax values are oil-saturated carbonates, and those Tmax values are derived from oil, not kerogen.

The % Roe data from Tmax suggest a consistent trend over the 240 ft (73 m) interval reported. The Tmax increases from about 435 to 450degC (815 to 842degF) or 0.67 to 0.95% Roe. This is indicative of a very high paleogeothermal gradient, suggesting a very high heat flux. Zones with low Tmax values are oil-saturated carbonates, and those Tmax values are derived from oil, not kerogen.

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* TAG Oil, 2010: http://www.tagoil.com/fractured-shale.asp (accessed August 27, 2010).

* TAG Oil, 2010: http://www.tagoil.com/fractured-shale.asp (accessed August 27, 2010).

* Tanck, G. S., 1997, Distribution and origin of organic carbon in the Upper Cretaceous Niobrara Formation and Sharon Springs Member of the Pierre Shale, Western Interior, United States: Ph.D. thesis, University of Arizona, Tuscon, Arizona, 411 p.

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* Toreador Resources: 2010, Paris Basin shale oil: Toreador taking the lead, Unconventional Oil 2010, October 12, 2010, London: http://www.toreador.net/images/presentations/Toreador_Unconventional_Oil_2010.pdf.

* Toreador Resources: 2010, Paris Basin shale oil: Toreador taking the lead, Unconventional Oil 2010, October 12, 2010, London: http://www.toreador.net/images/presentations/Toreador_Unconventional_Oil_2010.pdf.

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* van Krevelen, D. C., 1961, Coal: New York, Van Nostrand Reinhold, 514 p.

* van Krevelen, D. C., 1961, Coal: New York, Van Nostrand Reinhold, 514 p.

* Vermillion Energy, 2010, November 2010 investor report: http://www.vermilionenergy.com/files/Presentations/November%20Investor%20Presentation_web.pdf (accessed November 11, 2010).

* Vermillion Energy, 2010, November 2010 investor report: http://www.vermilionenergy.com/files/Presentations/November%20Investor%20Presentation_web.pdf (accessed November 11, 2010).