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 unit equipped with a Total Organic Carbon analysis module. A typical Rock-Eval experiment was initiated with heating of a pulverized rock sample at 300ºC 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 600ºC at a rate of 25ºC/min and decomposition of kerogen occurs. The final stage involves oxidation and combustion of the residual organic matter at 600ºC. The amount of hydrocarbons volatilized at 300ºC and evolved from kerogen at 300ºC to 600ºC 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 300ºC to 390ºC, determined by a thermal conductivity detector, comprises the S3 peak. The percentage of carbon in CO2 formed during oxidation at 600ºC 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 (Espitalie 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 Espitalie et al. (1985) the oil window is defined by the following Tmax ranges: 440º-448ºC (Type I), 430º-455ºC (Type II) and 430º-470ºC (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.

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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