Changes

The present-day TOC (TOCpd) values for the Mowry Shale only average 1.95%, with an estimated original TOC (TOCo) of 2.43%. The original hydrogen index (HIo) values average about 183 mg HC/g TOC, with a range from 128 to 400 mg/g. Based on the expulsion curves of Pepper<ref name=Ppper1992 /> based on original hydrogen index (HIo) values, such a system will expel between 0 and 50% of its generated products and, therefore, should retain a high percentage of generated products. At higher thermal maturities, peak to late oil window, the oil quality should be condensate-like in terms of API gravity. Oil crossover effect is noted in various intervals in Mowry Shale wells, but also in the underlying Muddy Formation sands that are produced as conventional reservoirs.

The present-day TOC (TOCpd) values for the Mowry Shale only average 1.95%, with an estimated original TOC (TOCo) of 2.43%. The original hydrogen index (HIo) values average about 183 mg HC/g TOC, with a range from 128 to 400 mg/g. Based on the expulsion curves of Pepper<ref name=Ppper1992 /> based on original hydrogen index (HIo) values, such a system will expel between 0 and 50% of its generated products and, therefore, should retain a high percentage of generated products. At higher thermal maturities, peak to late oil window, the oil quality should be condensate-like in terms of API gravity. Oil crossover effect is noted in various intervals in Mowry Shale wells, but also in the underlying Muddy Formation sands that are produced as conventional reservoirs.

A geochemical log of the Home Petroleum 2-Phoenix Unit in Johnson County, Wyoming, shows oil crossover in the Mowry Shale at 3478.51 m (11,412.4 ft) (Figure 13). The oil yield is reasonably high in this interval of 17.7 m (58 ft). This computes to about 2.385 times 105 m3/2.589988 km2 (1,500,000 bbl/mi2) using unadjusted S1 values.

A geochemical log of the Home Petroleum 2-Phoenix Unit in Johnson County, Wyoming, shows oil crossover in the Mowry Shale at 3478.51 m (11,412.4 ft) ([[:File:M97Ch1.2FG13.jpg|Figure 13]]). The oil yield is reasonably high in this interval of 17.7 m (58 ft). This computes to about 2.385 times 105 m3/2.589988 km2 (1,500,000 bbl/mi2) using unadjusted S1 values.

====Cody and Mowry Shales, Bighorn Basin====

====Cody and Mowry Shales, Bighorn Basin====

[[File:M97Ch1.2FG14.jpg|thumb|500px|{{figure number|14}}Geochemical log of the Gulf Exploration Corp. 1-31-3D-Predicament well, Bighorn Basin. The Cody and Mowry shales show the oil crossover as do the Eagle and Muddy sands. TOC = total organic carbon; S1 = Rock-Eval measured oil contents; S2 = Rock-Eval measured kerogen yields.]]

[[File:M97Ch1.2FG14.jpg|thumb|500px|{{figure number|14}}Geochemical log of the Gulf Exploration Corp. 1-31-3D-Predicament well, Bighorn Basin. The Cody and Mowry shales show the oil crossover as do the Eagle and Muddy sands. TOC = total organic carbon; S1 = Rock-Eval measured oil contents; S2 = Rock-Eval measured kerogen yields.]]

There is no announced discovery of a shale-oil resource system in the Mowry Shale of the Bighorn basin, although it is speculated to be a potential shale-oil resource system much as in the Powder River Basin. An example for potential production is given by the Gulf Exploration Corp. 1-31-3D-Predicament well in Big Horn County, Wyoming. A geochemical log demonstrates oil crossover in the Cody and Mowry shales, with high amounts of oil particularly in the Cody Shale (Figure 14). The Cody Shale shows more than 580 m (1900 ft) of oil crossover suggestive of more than 3.56 times 106 m3/km2 (106 million bbl/mi2) of oil (uncorrected for evaporative losses). At this depth with the high OSI values, it is anticipated that this is open-fractured Cody Shale. Oil also exists in the overlying Eagle Formation sands. Calculated TOCo values range from 2.05 to 4.31%, with HIo values ranging from 78 to 642 mg HC/g TOC. The highest value is a bit anomalous compared with the other five samples of the Cody Shale that only range from 1.94 to 2.65% TOCo and 78 to 284 mg HC/g TOC for HIo.

There is no announced discovery of a shale-oil resource system in the Mowry Shale of the Bighorn basin, although it is speculated to be a potential shale-oil resource system much as in the Powder River Basin. An example for potential production is given by the Gulf Exploration Corp. 1-31-3D-Predicament well in Big Horn County, Wyoming. A geochemical log demonstrates oil crossover in the Cody and Mowry shales, with high amounts of oil particularly in the Cody Shale ([[File:M97Ch1.2FG14.jpg|Figure 14]]). The Cody Shale shows more than 580 m (1900 ft) of oil crossover suggestive of more than 3.56 times 106 m3/km2 (106 million bbl/mi2) of oil (uncorrected for evaporative losses). At this depth with the high OSI values, it is anticipated that this is open-fractured Cody Shale. Oil also exists in the overlying Eagle Formation sands. Calculated TOCo values range from 2.05 to 4.31%, with HIo values ranging from 78 to 642 mg HC/g TOC. The highest value is a bit anomalous compared with the other five samples of the Cody Shale that only range from 1.94 to 2.65% TOCo and 78 to 284 mg HC/g TOC for HIo.

Oil crossover is apparent in the Mowry Shale and Muddy Formation at 3753.6 m (12,315 ft) and 3799.3 to 3826.7 m (12,465–12,555 ft).

Oil crossover is apparent in the Mowry Shale and Muddy Formation at 3753.6 m (12,315 ft) and 3799.3 to 3826.7 m (12,465–12,555 ft).

A well drilled in 2009 by Whiting Oil amp Gas Corp., the 43-18H-Threemile in San Juan County, Utah, in the Cane Creek Shale was reported to have 8 to 13% porosity, 10 to 50 microdarcys permeability, and 20 to 35% water saturation; and was highly overpressured with a pressure gradient of 21.218 kPa/m (0.938 psi/ft) (Rasmussen et al., 2010). The well was completed with an uncemented liner and swell packers with 11-stage stimulation every 152.4 m (500 ft), each with 49,895.16 kg (110,000 lb) of proppant and 318 m3 (2000 bbl) of gel (Rasmussen et al., 2010). The scout ticket shows an initial flow rate of 1.145 m3/day (72 bbl/day) of oil, 1080 m3/day (38 mcf/day) of gas, and 31.16 m3/day (196 bbl/day) of water, but the well has since produced 1722 m3 (10,832 bbl) of oil, 5.16 times 104 m3 (1821 mcf) of gas, and 8863 m3 (55,745 bbl) of water, with a maximum GOR of 134.83 m3/m3 (757 scf/bbl) (IHS Energy News on Demand, 2010).

A well drilled in 2009 by Whiting Oil amp Gas Corp., the 43-18H-Threemile in San Juan County, Utah, in the Cane Creek Shale was reported to have 8 to 13% porosity, 10 to 50 microdarcys permeability, and 20 to 35% water saturation; and was highly overpressured with a pressure gradient of 21.218 kPa/m (0.938 psi/ft) (Rasmussen et al., 2010). The well was completed with an uncemented liner and swell packers with 11-stage stimulation every 152.4 m (500 ft), each with 49,895.16 kg (110,000 lb) of proppant and 318 m3 (2000 bbl) of gel (Rasmussen et al., 2010). The scout ticket shows an initial flow rate of 1.145 m3/day (72 bbl/day) of oil, 1080 m3/day (38 mcf/day) of gas, and 31.16 m3/day (196 bbl/day) of water, but the well has since produced 1722 m3 (10,832 bbl) of oil, 5.16 times 104 m3 (1821 mcf) of gas, and 8863 m3 (55,745 bbl) of water, with a maximum GOR of 134.83 m3/m3 (757 scf/bbl) (IHS Energy News on Demand, 2010).

An example of the Pennsylvanian Cane Creek section is provided by a geochemical log of the Mobil Oil Corp. 12-3-Jakeys Ridge well (Figure 15). These data illustrate the high organic carbon content throughout this 755.9 m (5760.81 ft) interval of the Cane Creek Shale, with an overall average of 7.67%. However, four distinct intervals are present, with average TOC values over the uppermost interval of 67 m (219.81 ft) with 1.34%, 146.3 m (479.98 ft) of 4.91%, 231.7 m (701.11 ft) of 13.49%, and 42.7 m (140.09 ft) of 6.61%. Although extremely high oil contents (S1) are present in the organic-rich interval, the values only exceed 100 mg/g at 2315.5 m (7596.76 ft), whereas the uppermost lean zone in this well has the highest OSI values averaging 120 mg/g over 67 m (219.81 ft). Thermal maturity is middle oil window based on the % Roe from Tmax measurements. The present-day hydrogen index (HIpd) values are low given this level of thermal maturity, suggesting either high-level conversion at this thermal maturity or lower than expected HIo values. The HIo values are estimated to have been 123, 265, 475, and 356 mg/g for the four different organic richness zones previously described.

An example of the Pennsylvanian Cane Creek section is provided by a geochemical log of the Mobil Oil Corp. 12-3-Jakeys Ridge well ([[:File:M97Ch1.2FG15.jpg|Figure 15]]). These data illustrate the high organic carbon content throughout this 755.9 m (5760.81 ft) interval of the Cane Creek Shale, with an overall average of 7.67%. However, four distinct intervals are present, with average TOC values over the uppermost interval of 67 m (219.81 ft) with 1.34%, 146.3 m (479.98 ft) of 4.91%, 231.7 m (701.11 ft) of 13.49%, and 42.7 m (140.09 ft) of 6.61%. Although extremely high oil contents (S1) are present in the organic-rich interval, the values only exceed 100 mg/g at 2315.5 m (7596.76 ft), whereas the uppermost lean zone in this well has the highest OSI values averaging 120 mg/g over 67 m (219.81 ft). Thermal maturity is middle oil window based on the % Roe from Tmax measurements. The present-day hydrogen index (HIpd) values are low given this level of thermal maturity, suggesting either high-level conversion at this thermal maturity or lower than expected HIo values. The HIo values are estimated to have been 123, 265, 475, and 356 mg/g for the four different organic richness zones previously described.

====Cretaceous Tuscaloosa Marine Shale, Louisiana====

====Cretaceous Tuscaloosa Marine Shale, Louisiana====

Limited data are available on the TMS, but an article by Miranda and Walters (1992) provides detailed analyses of an upper-middle Tuscaloosa Shale core. Sun Oil Corp. drilled the 1-Spinks well in Pike County, Mississippi, taking 94.5 m (310 ft) of core. They report the core as having dark-gray fissile shale with occasional thin (5–25 cm [2–10 in.]) sand intervals. The well was perforated in three different intervals between 3356.15 and 3366.21 m (11,011–11,044 ft), but no oil or gas flow was recorded.

Limited data are available on the TMS, but an article by Miranda and Walters (1992) provides detailed analyses of an upper-middle Tuscaloosa Shale core. Sun Oil Corp. drilled the 1-Spinks well in Pike County, Mississippi, taking 94.5 m (310 ft) of core. They report the core as having dark-gray fissile shale with occasional thin (5–25 cm [2–10 in.]) sand intervals. The well was perforated in three different intervals between 3356.15 and 3366.21 m (11,011–11,044 ft), but no oil or gas flow was recorded.

A geochemical log of this well illustrates the extremely low carbonate and organic carbon contents, low OSI values, and about 1 to 2% sulfur throughout the sampled interval (Figure 16). The TOCpd values average only 0.84% with a range of 0.21 to 1.36%. Miranda and Walters (1992) estimate about 20% conversion of organic matter. As such, TOCo values would only increase to about 0.92% or a range of 0.25 to 1.60%. The HIo values are estimated to be on the low end of marine shales at 284 mg HC/g TOC on average with a range of 150 to 402 mg HC/g TOC. Not only is the Tuscaloosa organic lean, but it also has extremely low carbonate (sim1%) and about 2% sulfur contents. The conversion of pyrolysis yields to oil would yield about 7.27 times 104 m3 (1.184 million bbl/mi2). Over the 15,280.93 km2 (5900 mi2) of Tuscaloosa deposition, this would amount to just about 1.11 times 109 m3 (7 billion bbl) of oil equivalent with a very high retention of generated oil based on the low HIo values, as previously predicted by John et al. (1997). The issue is not with this estimate, but being able to recover even a minimal percentage of this volume of oil. Such a low carbonate shale-oil resource system will be one of the most difficult systems to stimulate and achieve good and enduring oil flow. However, it should be noted that the clay and quartz contents are not known. Based on the organic matter, Tuscaloosa sourced oil would be a high API gravity oil or condensate, but with sulfur present. The better likelihood for production is the closely associated sands. This type of system remains a significant challenge to developing similar unconventional shale-oil plays.

A geochemical log of this well illustrates the extremely low carbonate and organic carbon contents, low OSI values, and about 1 to 2% sulfur throughout the sampled interval ([[:File:M97Ch1.2FG16.jpg|Figure 16]]). The TOCpd values average only 0.84% with a range of 0.21 to 1.36%. Miranda and Walters (1992) estimate about 20% conversion of organic matter. As such, TOCo values would only increase to about 0.92% or a range of 0.25 to 1.60%. The HIo values are estimated to be on the low end of marine shales at 284 mg HC/g TOC on average with a range of 150 to 402 mg HC/g TOC. Not only is the Tuscaloosa organic lean, but it also has extremely low carbonate (sim1%) and about 2% sulfur contents. The conversion of pyrolysis yields to oil would yield about 7.27 times 104 m3 (1.184 million bbl/mi2). Over the 15,280.93 km2 (5900 mi2) of Tuscaloosa deposition, this would amount to just about 1.11 times 109 m3 (7 billion bbl) of oil equivalent with a very high retention of generated oil based on the low HIo values, as previously predicted by John et al. (1997). The issue is not with this estimate, but being able to recover even a minimal percentage of this volume of oil. Such a low carbonate shale-oil resource system will be one of the most difficult systems to stimulate and achieve good and enduring oil flow. However, it should be noted that the clay and quartz contents are not known. Based on the organic matter, Tuscaloosa sourced oil would be a high API gravity oil or condensate, but with sulfur present. The better likelihood for production is the closely associated sands. This type of system remains a significant challenge to developing similar unconventional shale-oil plays.

====Heath Shale====

====Heath Shale====

The TOC data from Cole and Drozd (1994) show an average TOC of 7.6% on 32 core samples from Fergus County, Montana, although the authors state that the thickness of the source rock is less than 10 m (20–30 ft), with calcareous shales being the best source rock intervals. They also state that “a large part of generated hydrocarbons remained within the source rock interval” (p. 382). Thermal maturity values range from immature to late oil window primarily in parts of Musselshell, Rosebud, and Garfield counties (Cole and Drozd, 1994).

The TOC data from Cole and Drozd (1994) show an average TOC of 7.6% on 32 core samples from Fergus County, Montana, although the authors state that the thickness of the source rock is less than 10 m (20–30 ft), with calcareous shales being the best source rock intervals. They also state that “a large part of generated hydrocarbons remained within the source rock interval” (p. 382). Thermal maturity values range from immature to late oil window primarily in parts of Musselshell, Rosebud, and Garfield counties (Cole and Drozd, 1994).

The Continental 1-Staunton well illustrates the variability in various geochemical characteristics of the Heath Shale. (Figure 17). The average TOC value is 4.52% in this well, but the range is 0.20 to 13.66% with a high standard deviation of 5.20%. Carbonate carbon data are not available. The pyrolysis yields (present-day Rock-Eval measured kerogen [S2pd]) and HIpd are also highly variable, with HIpd values averaging 315 mg HC/g TOC, with a range of 137 to 523 mg HC/g TOC. Thermal maturity is early oil window with % Roe from Tmax values of 0.51 to 0.72%. Conversion of organic matter is thus likely about 10 to 20%.

The Continental 1-Staunton well illustrates the variability in various geochemical characteristics of the Heath Shale. ([[:File:M97Ch1.2FG17.jpg|Figure 17]]). The average TOC value is 4.52% in this well, but the range is 0.20 to 13.66% with a high standard deviation of 5.20%. Carbonate carbon data are not available. The pyrolysis yields (present-day Rock-Eval measured kerogen [S2pd]) and HIpd are also highly variable, with HIpd values averaging 315 mg HC/g TOC, with a range of 137 to 523 mg HC/g TOC. Thermal maturity is early oil window with % Roe from Tmax values of 0.51 to 0.72%. Conversion of organic matter is thus likely about 10 to 20%.

The oil crossover effect is noted in two samples: one at 778.76 m (2555 ft) and another at the base, 815.34 m (2675 ft); both are organic lean with 0.41% and 0.20% TOC, respectively, characteristic of hybrid shale-oil resource systems, and these may be the zones to target in future drilling efforts.

The oil crossover effect is noted in two samples: one at 778.76 m (2555 ft) and another at the base, 815.34 m (2675 ft); both are organic lean with 0.41% and 0.20% TOC, respectively, characteristic of hybrid shale-oil resource systems, and these may be the zones to target in future drilling efforts.

Similarly, the Ordovician Utica Shale shows oil crossover in parts of New York, Pennsylvania, Ohio, and Michigan.

Similarly, the Ordovician Utica Shale shows oil crossover in parts of New York, Pennsylvania, Ohio, and Michigan.

A plot of TOC versus oil for both Marcellus and Utica shales shows the crossover effect even in areas where the shales show a high level of conversion indicative of gas window thermal maturity (Figure 18). This could be contamination or migrated oil.

A plot of TOC versus oil for both Marcellus and Utica shales shows the crossover effect even in areas where the shales show a high level of conversion indicative of gas window thermal maturity ([[:File:M97Ch1.2FG18.jpg|Figure 18]]). This could be contamination or migrated oil.

====Permian Basin====

====Permian Basin====