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→Predicting gas destruction
==Predicting gas destruction==
==Predicting gas destruction==
It is not the destruction of methane as much as the lack of economic [[accumulation]]s which occurs at higher maturation levels. Methane occurs in fluid inclusions from lower crustal depths, and shows of methane are not unusual where drilling through low-grade metamorphic rocks—even those at a grade high enough to contain graphite instead of kerogen (R<sub>0</sub> > 8%). For example the Shell Barret #1 well in Hill County, Texas, had a 30-minute methane flare at over [[depth::13,000 ft]] depth in rock described as dolomite and calcite marble with graphitic inclusions.<ref name=ch11r30>Rozendal, R., A., Erskine, W., S., 1971, [http://archives.datapages.com/data/bulletns/1971-73/data/pg/0055/0011/2000/2008.htm Deep test in Ouachita structural belt of Central Texas]: AAPG Bulletin, vol. 56, p. 2008–2017.</ref>
It is not the destruction of methane as much as the lack of economic [[accumulation]]s which occurs at higher maturation levels. Methane occurs in fluid inclusions from lower crustal depths, and shows of methane are not unusual where drilling through low-grade metamorphic rocks—even those at a grade high enough to contain graphite instead of kerogen (R<sub>0</sub> > 8%). For example the Shell Barret #1 well in Hill County, Texas, had a 30-minute methane flare at over [[depth::13,000 ft]] depth in rock described as dolomite and calcite marble with graphitic inclusions.<ref name=ch11r30>Rozendal, R. A., and W. S. Erskine, 1971, [http://archives.datapages.com/data/bulletns/1971-73/data/pg/0055/0011/2000/2008.htm Deep test in Ouachita structural belt of Central Texas]: AAPG Bulletin, vol. 56, p. 2008–2017.</ref>
The following characteristics can help us predict and recognize gas destruction:
The following characteristics can help us predict and recognize gas destruction:
* Economic gas [[accumulation]]s become more unusual with maturation levels > 2.8% R<sub>o</sub>.<ref name=ch11r3>Bartenstein, H., 1980, Coalification in NW Germany: Erdöl und Kohle-Erdgas-Petrochemie: vol. 33, p. 121–125.</ref> This is the traditional base of the gas preservation zone.
* Economic gas [[accumulation]]s become more unusual with maturation levels > 2.8% R<sub>o</sub>.<ref name=ch11r3>Bartenstein, H., 1980, Coalification in NW Germany: Erdöl und Kohle-Erdgas-Petrochemie: vol. 33, p. 121–125.</ref> This is the traditional base of the gas preservation zone.
* The major gas accumulation with the highest well-documented maturity level where [[Calculating charge volume|charging]] occurred before or during exposure to the high temperatures occurs at a maturation level 3.5–3.8% R<sub>o</sub> equivalent (Wilburton field, Oklahoma).<ref name=ch11r13>Hendrick, S., J., 1992, Vitrinite reflectance and deep Arbuckle maturation at Wilburton field, Latimer County, OK: Oklahoma Geological Survey Circular 93, p. 176–184.</ref>
* The major gas accumulation with the highest well-documented maturity level where [[Calculating charge volume|charging]] occurred before or during exposure to the high temperatures occurs at a maturation level 3.5–3.8% R<sub>o</sub> equivalent (Wilburton field, Oklahoma).<ref name=ch11r13>Hendrick, S. J., 1992, Vitrinite reflectance and deep Arbuckle maturation at Wilburton field, Latimer County, OK: Oklahoma Geological Survey Circular 93, p. 176–184.</ref>
==Gas dilution==
==Gas dilution==