Changes

==Oil crossover effect==

==Oil crossover effect==

[[File:M97Ch1.2FG2.jpg|thumb|500px|{{figure number|2}}Example of oil crossover effect in productive Bazhenov Shale, West Siberian Basin, Russia. Data derived from graphic plots in Lopatin et al. (2003) illustrate that when free oil from Rock-Eval measured oil content (S1) exceeds total organic carbon (TOC) on an absolute basis, potentially producible oil is present. The oil saturation index (OSI) is simply (S1 times 100)/TOC, giving results in mg HC/g TOC. As such, when the OSI is greater than 100 mg/g, potentially producible oil is present.<ref name=J&B1984 />]]

[[File:M97Ch1.2FG2.jpg|thumb|500px|{{figure number|2}}Example of oil crossover effect in productive Bazhenov Shale, West Siberian Basin, Russia. Data derived from graphic plots in Lopatin et al.<ref name=Lptn2003>Lopatin, N. V., S. L. Zubairaev, I. M. Kos, T. P. Emets, E. A. Romanov, and O. V. Malchikhina, 2003, Unconventional oil accumulations in the Upper Jurassic Bazhenov Black Shale Formation, West Siberian Basin: A self-sourced reservoir system: Journal of Petroleum Geology, v. 26, no. 2, p. 225–244, doi:10.1111/j.1747-5457.2003.tb00027.x.</ref> illustrate that when free oil from Rock-Eval measured oil content (S1) exceeds total organic carbon (TOC) on an absolute basis, potentially producible oil is present. The oil saturation index (OSI) is simply (S1 times 100)/TOC, giving results in mg HC/g TOC. As such, when the OSI is greater than 100 mg/g, potentially producible oil is present.<ref name=J&B1984 />]]

A geochemical indication of potentially producible oil is indicated by the oil crossover effect, that is, the crossover of oil content, either Rock-Eval S1 or EOM relative to organic richness (TOC, absolute values), or when the oil saturation index (OSI) (S1 times 100/TOC) reaches a value of about 100 mg hydrocarbons (HC)/g TOC. This is illustrated by graphic results describing Upper Jurassic Bazhenov Shale open-fractured shale-oil production. These data values are derived from the graphic of Lopatin et al. (2003) for Bazhenov shales in the 11-18-Maslikhov well, and they clearly show the oil crossover effect and the productive intervals ([[:File:M97Ch1.2FG2.jpg|Figure 2]]). Such high crossover in an organic-rich shale is indicative of an open-fracture network.

A geochemical indication of potentially producible oil is indicated by the oil crossover effect, that is, the crossover of oil content, either Rock-Eval S1 or EOM relative to organic richness (TOC, absolute values), or when the oil saturation index (OSI) (S1 times 100/TOC) reaches a value of about 100 mg hydrocarbons (HC)/g TOC. This is illustrated by graphic results describing Upper Jurassic Bazhenov Shale open-fractured shale-oil production. These data values are derived from the graphic of Lopatin et al.<ref name=Lptn2003 /> for Bazhenov shales in the 11-18-Maslikhov well, and they clearly show the oil crossover effect and the productive intervals ([[:File:M97Ch1.2FG2.jpg|Figure 2]]). Such high crossover in an organic-rich shale is indicative of an open-fracture network.

Rock-Eval S1 or EOM yields alone have little meaning in assessing potential production because they do not account for the organic background. For example, coals might have an S1 value of 10 mg HC/g rock, but with a TOC of 50% or higher, the OSI is quite low, indicative of low oil saturation with a high expulsion or production threshold.

Rock-Eval S1 or EOM yields alone have little meaning in assessing potential production because they do not account for the organic background. For example, coals might have an S1 value of 10 mg HC/g rock, but with a TOC of 50% or higher, the OSI is quite low, indicative of low oil saturation with a high expulsion or production threshold.

A geochemical log of this well demonstrates oil crossover in the 1371.6 to 1417.3 m (4500–4650 ft) interval (Figure 3). These results are from cuttings of this well that were archived and reanalyzed in 2010. The relatively high values for OSI suggest open fractures in the shale. The TOC values average about 2.2% with less than 25% carbonate. A deeper zone from 1493.5 to 1569.7 m (4900–5150 ft) shows a very high oil content but very little oil crossover and was not perforated. However, it would likely have flowed oil, although the rate would have been low, depending on oil quality. Whereas free oil yields (S1) are high (as much as 0.0108 m3/m3 or 80 bbl/ac-ft), there is also a very high remaining generation potential (S2) indicative of low thermal maturity, although some of this is likely extractable organic matter (EOM) carryover given the low API gravity of the oil. Thus, the total oil content is higher, and the S2 and HI are lower; extraction and reanalysis would provide the total oil yield. For example, data on whole rock and extracted rock from the Getty 163-Los Alamos well, Santa Maria Basin onshore, demonstrate that only 15–30% of the oil is found in Rock-Eval S1, whereas the bulk is found in Rock-Eval S2. This carryover effect is a function of oil quality, especially API gravity, but also the lithofacies.

A geochemical log of this well demonstrates oil crossover in the 1371.6 to 1417.3 m (4500–4650 ft) interval (Figure 3). These results are from cuttings of this well that were archived and reanalyzed in 2010. The relatively high values for OSI suggest open fractures in the shale. The TOC values average about 2.2% with less than 25% carbonate. A deeper zone from 1493.5 to 1569.7 m (4900–5150 ft) shows a very high oil content but very little oil crossover and was not perforated. However, it would likely have flowed oil, although the rate would have been low, depending on oil quality. Whereas free oil yields (S1) are high (as much as 0.0108 m3/m3 or 80 bbl/ac-ft), there is also a very high remaining generation potential (S2) indicative of low thermal maturity, although some of this is likely extractable organic matter (EOM) carryover given the low API gravity of the oil. Thus, the total oil content is higher, and the S2 and HI are lower; extraction and reanalysis would provide the total oil yield. For example, data on whole rock and extracted rock from the Getty 163-Los Alamos well, Santa Maria Basin onshore, demonstrate that only 15–30% of the oil is found in Rock-Eval S1, whereas the bulk is found in Rock-Eval S2. This carryover effect is a function of oil quality, especially API gravity, but also the lithofacies.

Other examples of open-fractured shale-oil production include the Niobrara, Pierre (U.S. Geological Survey, 2003), Upper Bakken shale-oil systems (North Dakota Geological Survey, 2010), and the West Siberian Jurassic Bazhenov Shale (Lopatin et al., 2003).

Other examples of open-fractured shale-oil production include the Niobrara, Pierre (U.S. Geological Survey, 2003), Upper Bakken shale-oil systems (North Dakota Geological Survey, 2010), and the West Siberian Jurassic Bazhenov Shale.<ref name=Lptn2003 />

A second Monterey Shale example is a deep Monterey Shale well drilled by Coastal Oil amp Gas in a synclinal part of the onshore Santa Maria Basin. The Coastal Oil amp Gas (OampG) Corp. 3-Hunter-Careaga well, Careaga Canyon field, flowed 53.9 m3/day (339 bbl/day) of 33deg API oil with 1.85 times 104 m3/day (653 mcf/day) of gas and 15 m3/day (95 bbl) of formation water from the Monterey Shale (scout ticket). It had a reported GOR of 343 m3/m3 (1926 scf/bbl). The well was perforated over numerous intervals from 2740 to 3711 m (8990–12,175 ft) with a maximum flow of 8.2 m3/day (516 bbl/day) and 2.20 times 104 m3/day (778 mcf/day). A geochemical log of this well illustrates its much higher thermal maturity, explaining the high GOR for a Monterey Shale well (Figure 4). The TOC values are variable, ranging from just under 3.00% to less than 0.50%. The highest oil crossover tends to occur where TOC values are lowest, suggesting variable lithofacies, but not open fractures as the oil crossover is marginal, reaching about 100 mg/g (average, 94 mg/g) in the 2793 to 3048 m (9165 to 10,000 ft) interval, with isolated exceptions over 100 mg/g at 3269 to 3305 m (10,725–10,845 ft) and 3580 to 3616 m (11,745–11,865 ft). Based on these data, the optimum interval for landing a horizontal would be in the 2903 to 2940 m (9525 to 9645 ft) zone, although multiple zones with OSI greater than 100 would flow oil. Additional oil likely exists in the pyrolysis (S2) peak because low TOC samples have substantial pyrolysis yields with some of the highest HI values, again indicative of oil carryover into the pyrolysis yield. Thermal maturity, as indicated by vitrinite reflectance equivalency (Roe) from Tmax, suggests maturity values spanning the entire oil window with the early oil window at 2743.2 m (9000 ft) and latest oil window at 3657.6 m (12,000 ft).

A second Monterey Shale example is a deep Monterey Shale well drilled by Coastal Oil amp Gas in a synclinal part of the onshore Santa Maria Basin. The Coastal Oil amp Gas (OampG) Corp. 3-Hunter-Careaga well, Careaga Canyon field, flowed 53.9 m3/day (339 bbl/day) of 33deg API oil with 1.85 times 104 m3/day (653 mcf/day) of gas and 15 m3/day (95 bbl) of formation water from the Monterey Shale (scout ticket). It had a reported GOR of 343 m3/m3 (1926 scf/bbl). The well was perforated over numerous intervals from 2740 to 3711 m (8990–12,175 ft) with a maximum flow of 8.2 m3/day (516 bbl/day) and 2.20 times 104 m3/day (778 mcf/day). A geochemical log of this well illustrates its much higher thermal maturity, explaining the high GOR for a Monterey Shale well (Figure 4). The TOC values are variable, ranging from just under 3.00% to less than 0.50%. The highest oil crossover tends to occur where TOC values are lowest, suggesting variable lithofacies, but not open fractures as the oil crossover is marginal, reaching about 100 mg/g (average, 94 mg/g) in the 2793 to 3048 m (9165 to 10,000 ft) interval, with isolated exceptions over 100 mg/g at 3269 to 3305 m (10,725–10,845 ft) and 3580 to 3616 m (11,745–11,865 ft). Based on these data, the optimum interval for landing a horizontal would be in the 2903 to 2940 m (9525 to 9645 ft) zone, although multiple zones with OSI greater than 100 would flow oil. Additional oil likely exists in the pyrolysis (S2) peak because low TOC samples have substantial pyrolysis yields with some of the highest HI values, again indicative of oil carryover into the pyrolysis yield. Thermal maturity, as indicated by vitrinite reflectance equivalency (Roe) from Tmax, suggests maturity values spanning the entire oil window with the early oil window at 2743.2 m (9000 ft) and latest oil window at 3657.6 m (12,000 ft).

===West Siberian Basin===

===West Siberian Basin===

An open-fractured shale-oil resource system is the Upper Jurassic Bazhenov Shale of the intracratonic West Siberian Basin (Lopatin et al., 2003). The Bazhenov Shale is a marine type II kerogen that is the primary source rock in the West Siberian Basin, with TOC values ranging from 5 to 35%, typically exceeding 15% (Lopatin et al., 2003). Production rates of 50 to 1700 m3/well (315–10,700 bbl/well) have been achieved from this system, which is mostly governed by identification of highly fractured shale with 10 to 12% porosity that still requires stimulation (Lopatin et al., 2003). Intervals dominated by siliceous or carbonate lithologies have the best reservoir properties, with 10 to 12% porosity and permeabilities typically less than 0.01 md (Lopatin et al., 2003).

An open-fractured shale-oil resource system is the Upper Jurassic Bazhenov Shale of the intracratonic West Siberian Basin.<ref name=Lptn2003 /> The Bazhenov Shale is a marine type II kerogen that is the primary source rock in the West Siberian Basin, with TOC values ranging from 5 to 35%, typically exceeding 15%.<ref name=Lptn2003 /> Production rates of 50 to 1700 m3/well (315–10,700 bbl/well) have been achieved from this system, which is mostly governed by identification of highly fractured shale with 10 to 12% porosity that still requires stimulation.<ref name=Lptn2003 /> Intervals dominated by siliceous or carbonate lithologies have the best reservoir properties, with 10 to 12% porosity and permeabilities typically less than 0.01 md.<ref name=Lptn2003 />

As shown in Figure 2, oil crossover occurs in the geochemical logs of the 11-18-Maslikhov well. In the interval from approximately 2904 to 2916 m (sim9527–9567 ft), oil crossover is very high, suggestive of high free oil content in open-fractured shale (instead of tight shale, although the 2909 m [9543.9 ft] sample is not likely fractured). As stated by Lopatin et al. (2003), the production risk is primarily controlled by thermal maturity and fractures in the shale.

As shown in Figure 2, oil crossover occurs in the geochemical logs of the 11-18-Maslikhov well. In the interval from approximately 2904 to 2916 m (sim9527–9567 ft), oil crossover is very high, suggestive of high free oil content in open-fractured shale (instead of tight shale, although the 2909 m [9543.9 ft] sample is not likely fractured). As stated by Lopatin et al.,<ref name=Lptn2003 /> the production risk is primarily controlled by thermal maturity and fractures in the shale.

===Paris Basin, France===

===Paris Basin, France===

* John, C., B. L. Jones, J. E. Moncrief, R. Bourgeois, and B. J. Harder, 1997, An unproven unconventional seven-billion barrel oil resource: The Tuscaloosa Marine Shale: http://www.lgs.lsu.edu/deploy/uploads/Tuscaloosa%20Marine%20Shale.pdf (accessed November 12, 2010).

* John, C., B. L. Jones, J. E. Moncrief, R. Bourgeois, and B. J. Harder, 1997, An unproven unconventional seven-billion barrel oil resource: The Tuscaloosa Marine Shale: http://www.lgs.lsu.edu/deploy/uploads/Tuscaloosa%20Marine%20Shale.pdf (accessed November 12, 2010).

* Johnson, M. S., 2009, Parshall field, North Dakota: Discovery of the year for the Rockies and beyond: Adapted from the oral presentation at AAPG Annual Convention, Denver, Colorado, June 7–10, 2009, Search and Discovery article 20081, posted September 25, 2009, 29 p.

* Johnson, M. S., 2009, Parshall field, North Dakota: Discovery of the year for the Rockies and beyond: Adapted from the oral presentation at AAPG Annual Convention, Denver, Colorado, June 7–10, 2009, Search and Discovery article 20081, posted September 25, 2009, 29 p.

* Lopatin, N. V., S. L. Zubairaev, I. M. Kos, T. P. Emets, E. A. Romanov, and O. V. Malchikhina, 2003, Unconventional oil accumulations in the Upper Jurassic Bazhenov Black Shale Formation, West Siberian Basin: A self-sourced reservoir system: Journal of Petroleum Geology, v. 26, no. 2, p. 225–244, doi:10.1111/j.1747-5457.2003.tb00027.x.

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* Mango, F. D., 1997, The light hydrocarbons in petroleum: A critical review: Organic Geochemistry, v. 26, no. 7/8, p. 417–440.

* Mango, F. D., 1997, The light hydrocarbons in petroleum: A critical review: Organic Geochemistry, v. 26, no. 7/8, p. 417–440.