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Organic geochemical parameters include: (1) Rock-Eval data, including Tmax, S1, S2, S3, and plots of some indices, (2) extract and chromatographic data (i.e., several ratios and the shape of chromatograms), and (3) fluorescence colorimetry and 3-dimensional spectra of extracts.
Organic petrologic indicators are indispensable for assessing thermal maturity. Microscopic analysis provides a quality control of geochemical data and enables identification of kerogen mixtures and contaminants from caved rocks and drilling mud additives. Organic petrologic indicators are: (1) ranges of mean vitrinite reflectance (Ro) for the "oil window" (0.60-1.35%), for the onset of wet gas formation (0.90%), and for the occurrence of dry gas only (2.0%), (2) fluorescence observations and spectral measurements, such as double-peaked spectra for mature kerogen and a shift in its fluorescence at increasing maturity, extinguished when the oil floor is reached (parameters include spectral peaks, spectral ratio, F.C.I., and photochemical effect, and crude oil is microscopica ly identified by spectral data and kerogen liquefaction under UV-exposure), and (3) visual estimation of the TAI of spore colors in transmitted light.
Conclusions are routinely drawn only from those parameters that show reliable data from both geochemical and petrologic determinations. Lopatin calculations from maturity profiles in wells are used to determine both the thermal history of a basin and mature source rocks.
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