Experimental:

Rock-Eval/TOC analysis provides fast and reliable characterization of the quantity and quality of sedimentary organic matter, as well as its thermal maturity. Pyrolysis experiments were conducted using Delsi Rock-Eval II and Rock-Eval VI units equipped with a Total Organic Carbon analysis module.

A typical Rock-Eval II experiment was initiated with heating of a pulverized rock sample at 300ēC for 3 min in helium atmosphere, when naturally occurring hydrocarbons (free and adsorbed) are volatilized. During the next stage, the oven temperature is steadily increased to 600ēC at a rate of 25ēC/min and decomposition of kerogen occurs. The final stage involves oxidation and combustion of the residual organic matter at 600ēC. The amount of hydrocarbons volatilized at 300ēC and evolved from kerogen at 300ēC to 600ēC is quantitatively determined by a flame ionization detector, and recorded as the S1 and S2 peaks, respectively. The temperature measured at the maximum of the S2 peak is referred to as Tmax. The quantity of organic CO2 generated from 300ēC to 390ēC, determined by a thermal conductivity detector, comprises the S3 peak. The percentage of carbon in CO2 formed during oxidation at 600ēC and in the hydrocarbon peaks S1 and S2 is used to define the total organic carbon content (TOC), expressed as a weight percentage. The determination of the quality of organic matter is based upon the calculation of Hydrogen (HI) and Oxygen (OI) indices (HI=S2/TOCx100, OI=S3/TOCx100) which are related to the atomic H/C and O/C ratios (Espitalié et al., 1977).

The OI versus HI cross plots ("pseudo van Krevelen diagrams") can be used as an organic matter type indicator at low and moderate maturities. The Tmax is an indicator of relative thermal maturity. According to Espitalié et al. (1985) the oil window is defined by the following Tmax ranges: 440ē-448ēC (Type I), 430ē-455ēC (Type II) and 430ē-470ēC (Type III). A cross plot of Tmax versus HI is used to constrain estimations of organic matter type and its thermal maturity, while the Production Index (PI=S1/[S1+S2]) is used to indicate staining of a sample or as an additional maturity parameter.

The tables also contain additional parameters specific to Rock-Eval 6 analysis that are not provided by the Rock-Eval II. These are % MINC which is the percent of carbon derived from inorganic sources and PC and RC which are the percent of pyrolyzable and residual (i.e. inert) carbon respectively, which together add up to % TOC. There are three OI values provided by the Rock-Eval 6 as this instrument is capable of distinguishing carbon monoxide (OICO) and carbon dioxide (not provided in tables) and these are combined to give the true Oxygen Index (OI). TPKS2 is the actual temperature in the oven at the top of the S2 peak. A correction is made to give a Tmax value equivalent to that provided by the Rock-Eval II instruments where the thermocouple was located further away from where the sample was pyrolized. For the majority of these samples, Tmax is about 39°C lower than the TPKS2 value.

References:

Espitalie, J., Laporte, J.L., Madec, M., Marquis, F., Leplat, P., Paulet, A. and Boutefeu, J., 1977. Methode rapide de characterisaion des roches meres de leur potential petrolier et de leur degre d'evolution. Revue de l'Institut Francais du Petrole vol. 32, p. 23-42.

Espitalie, J., Deroo, G. and Marquis, F. 1985. Rock Eval Pyrolysis and Its Applications. Preprint; Institut Francais du Petrole, Geologie No. 27299, 72 p. English translation of, La pyrolyse Rock-Eval et ses applications, Premiere, Deuxieme et Troisieme Parties, in Revue de l'Institut Francais du Petrole, v. 40, p. 563-579 and 755-784; v. 41, p. 73-89.



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