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* Gasification of oil in reservoirs is associated with the formation of pyrobitumen.<ref name=ch11r34>Tissot, B., P., Welte, D., H., 1984, Petroleum Formation and Occurrence, 2 ed.: New York, Springer-Verlag, 699 p. 460–461</ref>
* Gasification of oil in reservoirs is associated with the formation of pyrobitumen.<ref name=ch11r34>Tissot, B., P., Welte, D., H., 1984, Petroleum Formation and Occurrence, 2 ed.: New York, Springer-Verlag, 699 p. 460–461</ref>
* Displacement of oil from a trap by gas is associated with asphaltene precipitates and/or relatively unaltered oil stain.
* Displacement of oil from a trap by gas is associated with asphaltene precipitates and/or relatively unaltered oil stain.
* Absence of an oil leg in the trap prior to charging by gas is indicated by the absence of oil stain with heavy molecular components.
* Absence of an oil leg in the trap prior to [[Calculating charge volume|charging]] by gas is indicated by the absence of oil stain with heavy molecular components.
* In accumulations that have been gasified, the presence of pyrobitumen can significantly reduce reservoir [[permeability]] due to gas or condensate.
* In accumulations that have been gasified, the presence of pyrobitumen can significantly reduce reservoir [[permeability]] due to gas or condensate.
* 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 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==
* Presence of intrusives in the fetch area can indicate a potential for carbon dioxide dilution.<ref name=ch11r29>Parker, C., 1974, Geopressures and secondary [[porosity]] in the deep Jurassic of Mississippi: Transactions of the Gulf Coast Association of Geological Societies, vol. 24, p. 69–80.</ref>
* Presence of intrusives in the fetch area can indicate a potential for carbon dioxide dilution.<ref name=ch11r29>Parker, C., 1974, Geopressures and secondary [[porosity]] in the deep Jurassic of Mississippi: Transactions of the Gulf Coast Association of Geological Societies, vol. 24, p. 69–80.</ref>
* If reservoir rocks are associated with evaporite cements or beds, expect hydrogen sulfide if the reservoir is exposed to temperatures > [[temperature::150°C]] and iron is not present to remove the hydrogen sulfide.
* If reservoir rocks are associated with evaporite cements or beds, expect hydrogen sulfide if the reservoir is exposed to temperatures > [[temperature::150°C]] and iron is not present to remove the hydrogen sulfide.
* Nitrogen is released during the late stages of coal maturation.<ref name=ch11r18>Jüntgen, V., H., Karweil, J., 1966, Gasbildung and gasspeicherung in steinkohlenfluzen, I. gasbildung: Erdöl und Kohle-Erdgas-Petrochemie, vol. 19, p. 339–344.</ref> Therefore, if a prospect is charged by a type III source rock only during its late maturation stage (R<sub>o</sub> > 2.5%), nitrogen dilution is possible. High nitrogen gas content is also characteristic of evaporative settings and hydrocarbon-poor basins.
* Nitrogen is released during the late stages of coal maturation.<ref name=ch11r18>Jüntgen, V., H., Karweil, J., 1966, Gasbildung and gasspeicherung in steinkohlenfluzen, I. gasbildung: Erdöl und Kohle-Erdgas-Petrochemie, vol. 19, p. 339–344.</ref> Therefore, if a prospect is [[Calculating charge volume|charged]] by a type III source rock only during its late maturation stage (R<sub>o</sub> > 2.5%), nitrogen dilution is possible. High nitrogen gas content is also characteristic of evaporative settings and hydrocarbon-poor basins.
* Nonhydrocarbon gas concentrations in mature basins can be estimated from evaluating regional gas concentration trends.
* Nonhydrocarbon gas concentrations in mature basins can be estimated from evaluating regional gas concentration trends.