Changes

Although an oil crossover value of less than 100 mg HC/g TOC does not rule out the possibility of having producible oil, it does represent substantially higher risk based strictly on geochemical results. It may be that samples have been dried or more volatile liquids have evaporated, particularly in conventional reservoir lithofacies.

Although an oil crossover value of less than 100 mg HC/g TOC does not rule out the possibility of having producible oil, it does represent substantially higher risk based strictly on geochemical results. It may be that samples have been dried or more volatile liquids have evaporated, particularly in conventional reservoir lithofacies.

Finally, it is not only important to locate oil reservoirs, it is important also to assess the quality of the oil contained in the reservoir. Such techniques have been described<ref>Jarvie, D. M., A. Morelos, and Z. Han, 2001a, [http://www.wwgeochem.com/resources/Jarvie+2001+Williston+Basin+Petroleum+Systems+paper.pdf  Detection of pay zones and pay quality, Gulf of Mexico]: Gulf Coast Association of Geological Societies Transactions 51st Annual Convention, Shreveport, Louisiana, October 17–19, v. LI, p. 151–160.</ref> and are an essential part of assessing the economic value of a reservoir. Basic tests include determination of sulfur content, API gravity, viscosity, and yield of polar resin and asphaltene relative to nonpolar saturate and aromatic hydrocarbons. A quick screening approach is to use [[gas chromatography]] to predict oil quality based on the fingerprint derived from the rock extract; this is the same tool used on produced oil samples or recovered from reservoir tests.

Finally, it is not only important to locate oil reservoirs, it is important also to assess the quality of the oil contained in the reservoir. Such techniques have been described<ref>Jarvie, D. M., A. Morelos, and Z. Han, 2001a, [http://www.wwgeochem.com/resources/Jarvie+2001+Williston+Basin+Petroleum+Systems+paper.pdf  Detection of pay zones and pay quality, Gulf of Mexico]: Gulf Coast Association of Geological Societies Transactions 51st Annual Convention, Shreveport, Louisiana, October 17–19, v. LI, p. 151–160.</ref> and are an essential part of assessing the economic value of a reservoir. Basic tests include determination of sulfur content, API [[gravity]], viscosity, and yield of polar resin and asphaltene relative to nonpolar saturate and aromatic hydrocarbons. A quick screening approach is to use [[gas chromatography]] to predict oil quality based on the fingerprint derived from the rock extract; this is the same tool used on produced oil samples or recovered from reservoir tests.

==Oil crossover effect examples==

==Oil crossover effect examples==