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.
Cutting samples were obtained from the Geological Survey of Canada archive set for Alberta
and British Columbia wells and therefore a maximum of 100 mg of material is available for
any depth. Consequently, there is only one analysis at any depth and repeat analyses cannot
be run if an instrument failure is suspected. 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.
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