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Evaluation of petroleum source rocks with combine analytical data and kinetic analysis

Kokkinopoulou Aikaterini

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Summary

Basin and petroleum system modeling, which leads to the assessment of hydrocarbons’ resources, requires kerogen thermal transformation kinetics as input for the reconstruction of generation history. In most industrial studies reaction rates and frequency factors are selected from literature data, describing kerogens of similar origin and environment of deposition. It has been shown that this approach leads to significant inaccuracies. Alternatively, thermal decomposition reactions may be studied with thermal gravimetry (TG) experiments at various heating rates to approximate hydrocarbon generation processes allowing the thermal energy required for hydrocarbon generation under differing geological conditions to be inferred. Rock-Eval (RE) analytical pyrolysis method has been widely accepted as industry standard method in petroleum exploration studies to identify kerogen type and maturation level; while RE pyrolysis curve (S2) may be used to generate reaction kinetics. The method provides pyrolysis data in a rapid and sensitive way to obtain and as it has been shown, it estimates accurately the kinetic parameters. The kinetics of the thermal decomposition of kerogen are typically described as a series of independent and parallel 1st order quasi-irreversible reactions and expressed by a distribution of activation energy with a single fixed frequency factor. This assumption seems to be oversimplified; nevertheless, it is supported by observations of the source rock maturation in nature. In this work, a sample set of nineteen source rocks of known formation and age were used to demonstrate the ability of the RE method to provide accurate kinetic data, along with TGA method, comparable to the ones obtained from time-consuming and costly laboratory pyrolysis experiments. The data obtained by RE analysis and TG analysis were used as input for the software KINETICS 05. Kinetic data for the examined samples is reported. The kinetic data were further treated by a hierarchical clustering algorithm in order to draw conclusions regarding the way the samples should be treated. Furthermore, the influence of the matrix (inorganic content, presence of bitumens) was studied, using samples pretreated respectively, by HCl treatment and organic solvent extraction. The techniques proposed offer valuable insight into the properties of the rock. Kinetic data derived from TGA provide valuable information on the composition of the sample, especially if they combined with XRD analysis data of the same sample. The results of RE kinetic analysis indicate that the geometry of S2 peak may reveal the level of maturation of the source rock. Finally, the clustering algorithm sorted the samples based on increasing level of maturation, decreasing hydrocarbon petroleum potential and based on the formation each sample came from.

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