![]() |
![]() |
ROCK-EVAL/TOC GUIDELINES FOR INTERPRETATION Various authors have discussed guidelines for the interpretation of Rock-Eval data (e.g. Espitalié et al., 1977, 1985; Peters, 1986 Lafargue et al., 1998). Rock-Eval/TOC parameters have significance only above threshold TOC, S1 and S2 values. If TOC is less than less than or equal to 0.3% then all parameters have questionable significance. Oxygen Index (OI = S3/TOC) has questionable significance if TOC is less than or equal to 0.5% and Tmax if S2 values are less than about 0.20 mg HC/g rock. Results can be affected by mineral matrix effects, especially in lower TOC content samples. These either retain generated compounds, generally lowering the S1 or S2 peaks, while increasing Tmax, or can also liberate inorganic CO2 and thus increase S3 and OI. These effects are more significant if TOC, S1 and S2 are low. OI values greater than 150 mg/g TOC suggest either low TOC or a mineral matrix CO2 contribution during pyrolysis. Note that TOC and Hydrogen Index decrease with increasing thermal maturity due to hydrocarbon generation. A threshold of 2% TOC is generally believed to be necessary for rock to source economic accumulations of liquid hydrocarbons although units with lower TOC contents can contribute to gas accumulations. It should be emphasized strongly that the data presented here is from the analysis of all samples provided to the GSC laboratory over the years for Rock-Eval analysis. Thus samples represent a variety of facies and lithologies and not just those thought to be possible source rocks. This explains why many of the samples have very low TOC contents. Many of the samples from wells are cuttings and thus represent lithologies over a depth interval such as 10 m and hence will tend to have lower TOC contents than core samples or outcrop where one lithology was preferentially sampled. Formation names are those provided by the originator of the sample or the well operator and may not be correct or correspond to present day stratigraphy for the sample locality. In the accompanying files, the data is split between field and well samples and between the geological domains. Note that for some wells in the St. Lawrence Platform section (A160, A163, A185, A187, A194), drilling was spudded in tectonic slivers of the Humber Zone to end-up in the underlying autochthonous platform succession. They were listed in with the remaining A wells for consistency. For each of these data sub-sets, histograms of all TOC values are presented as well as HI versus OI plots where only those values with S2 higher than 0.2 mg HC/g rock are used. |
References for this section of text
Espitalié, 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 v. 32, p. 23-42. |
Espitalié, J., Deroo, G. and Marquis, F. (1985): Rock-Eval pyrolysis and its applications; Institut Francais du Petrole preprint #27299. Revue de l'Institut Francais du Petrole v. 41, p. 73-90. |
Lafargue, E., Espitalié, J., Marquis, F. and Pillot, D. 1998. Rock-Eval 6 applications in hydrocarbon exploration, production and soil contamination studies. Revue de l’Insitut Français du Petrole v. 53, 421-437. |
Peters, K. E., 1986. Guidelines for evaluating source rock using programmed pyrolysis; Bulletin of the American Association of Petroleum Geologists, v. 70, p. 318-329.. |
Return to main page | ![]() |