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* Analyzing geohistory or mapping maturation indicators can identify reservoir maturation levels where methane [[accumulation]]s may be uneconomic. Most sizable gas accumulations occurring at maturation levels > 2.8% R<sub>o</sub> have thick claystone seals that help preserve the accumulation.
* Analyzing geohistory or mapping maturation indicators can identify reservoir maturation levels where methane [[accumulation]]s may be uneconomic. Most sizable gas accumulations occurring at maturation levels > 2.8% R<sub>o</sub> have thick claystone seals that help preserve the accumulation.
* 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., and J. Karweil, 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.
* Nitrogen is released during the late stages of coal maturation.<ref name=ch11r18>Jüntgen, V. H., and J. Karweil, 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.