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S.B. Nielsen

Confidence limits on kinetic models of primary cracking and implications for the modelling of hydrocarbon generation

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Kinetic models of primary cracking for use in hydrocarbon modelling are obtained through empirical calibration against laboratory measurements. This paper utilizes least-squares variance analysis to evaluate the uncertainty in the calibrated kinetic parameters and discusses some consequences for the prediction of hydrocarbon generation. It is substantiated that the sensitivity of the average kinetic parameters Ea* and loge(A)* to micropyrolysis errors can be parameterized by errors in pyrolysis Tmax. The absolute and relative errors in Tmax are modelled by normal (Gaussian) random variables and the variance analysis yields the joint normal probability density distribution of variability in Ea* and loge(A)*. It is found that Tmax errors reduce the ability to resolve independently the values of Ea* and loge(A)*: the estimation errors are highly positively correlated and repeated measurements on identical kerogens will produce values of Ea* and loge(A)* which tend to fall close to and along the line loge(A)* = EaIRTp + constant, where Tp is an average pyrolysis temperature. This correlation is consistent with observations, and hence it is suggested that it is mainly an artifact which originates in the experimental errors of laboratory pyrolysis. When values of Ea* and loge(A)* are confined to the region of the confidence ellipsoid, the pyrolysis data are satisfied within their error bounds. However, the variability in predictions of hydrocarbon generation may be large depending on the particular geological temperature history. The uncertainties in the depth to the oil window may be several hundreds of metres, and the timing of peak hydrocarbon generation rate may vary considerably. The inclusion of basin geochemical data in the calibration drastically reduces the ambiguity in Ea* and loge(A)* and emphasizes the need to validate the laboratory calibrated kinetic models against basin observations.

Original languageEnglish
JournalMarine and Petroleum Geology
Pages (from-to)483-492
Number of pages10
Publication statusPublished - 1 Jan 1991
Externally publishedYes

    Research areas

  • hydrocarbon generation, kinetic modelling, primary cracking

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