Improved kinetic parameters of hydrocarbon generation based on open-system pyrolysis data
Date Issued
2010
Date
2010
Author(s)
Tseng, Yu-Hsin
Abstract
Kinetic information is essential to predict the temperature, timing or depth of hydrocarbon generation within a hydrocarbon system. The most common practice in basin modeling uses default kinetic parameters (activation energy, Ea and frequency factor, A) based on three major kerogen types. Recent study revealed that the use of the default parameters of kerogen type can introduce unacceptable errors into modeling, suggesting the necessity to consider the characteristics of individual target source, although the measurement of kinetic parameters is by no means routine. Therefore, this study aims at prediction of kinetic information for individual source rock using mainly its Rock-Eval parameters.
The present modeling revealed a systematic link between the shape of the discrete distribution of activation energies and the shapes of calculated reaction rates in both geological and laboratorial heating rates. New parameters were derived to quantify the similarities. Good correlations between lab-S2 and geo-S2 half high width with Ea half high width, strongly implying the resemblance in their shapes. Moreover, good correlation between the “selected Ea” and geo-Tpeak also suggests a delicate resemblance in the configuration of their shapes. Similarities in the shape of geo-S2 peak and lab-S2 peak with the shape of activation energy distribution may imply that it’s possible for deriving kinetic information with only Rock-Eval data, though more correlations may need for exact derivation; however, the role of activation energy in the reflection of reaction rates was utterly revealed.
Recently it has been shown that hydrous pyrolysis conditions could simulate the natural conditions better and its applications were supported by two case studies. The kinetic information from hydrous pyrolysis experiment was then required for accurately predicting hydrocarbon generation. However, the closed system hydrous pyrolysis experiment is much more tedious and needs large amount of samples relative to open-system pyrolysis. Therefore, the second aim of our study is the derivation of convincing distributed activation energies of hydrous pyrolysis from only routine open-system Rock-Eval data.
Our results unveiled that there was a good correlation between open-system Rock-Eval parameter Tmax and the activation energy (Ea) derived from hydrous pyrolysis. The single Ea of hydrous pyrolysis could be predicted from Tmax based on the correlation, while the frequency factor (A) was estimated based on the linear relationship between single Ea and log A. Because the Ea distribution is more rational than single Ea, we refined the predicted single hydrous pyrolysis Ea into a discrete distribution of Ea by shifting the pattern of Ea distribution from open-system pyrolysis until the weight mean Ea distribution equalled to the single hydrous pyrolysis Ea. Therefore, our predicted kinetic information can have the benefits of both experiments – the convincing Ea and A related to the hydrous pyrolysis and also the rational distribution of Ea from open-system Rock-Eval pyrolysis. Though such refined model with a discrete distribution of activation energies and frequency factors still need further verifications in the field, it showed in the transformation curves at geological heating rate were similar to that of original hydrous model still imply the adaptation for usage.
The study offers a new approach as a simple method for obtaining improved kinetic parameters of hydrous pyrolysis (better than using the kinetic parameters of open-system pyrolysis) with only routine open-system Rock-Eval data, which will allow us for better estimating hydrocarbon generation.
Subjects
hydrocarbon
kinetics
activation energy
Rock-Eval pyrolysis
hydrous pyrolysis
Type
thesis
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