Reconstructing Petroleum Migration Pathways Through Analysis of Polar Compounds

Introduction

The fundamental chemistry that controls the formation of liquid hydrocarbons from kerogen is being studied, to better understand petroleum formation and primary migration. The present study focuses on the formation and distribution of alkylphenols and alkylcarbazoles in crude oils and sediments in order to determine their applicability in the reconstruction of oil migration pathways.

Analysis of polar compounds: Chromatographic developments

A rapid small-scale method for the quOctober 16, 2006zoles and benzocarbazoles from sedimentary matter has been developed using liquid chromatography and GC-MS techniques. These components can now be easily, rapidly and economically separated from saturated and aromatic hydrocarbons using silica gel, as a stationary phase, and disposable glassware such as Pasteur pipettes (sample sizes up to 100 mg). Analysis of these components can be performed using GC-MS without any further derivatisation.

Formation of alkylphenols in crude oils and sediments

The acid catalysed hydroxylation of alkylbenzenes has been identified as a new formation mechanism for sedimentary alkylphenols. Laboratory experiments involving a Lewis acid catalysed hydroxylation of alkylbenzene mixtures, similar to crude oils, were shown to form alkylphenol distributions similar to those found in the crude oils. Crude oils with differing alkylbenzene distributions were shown to have different alkylphenol distributions, explainable through an acid catalysed hydroxylation mechanism. These results suggest that sedimentary alkylphenols can form through acid catalysed hydroxylation of alkylbenzenes, which accounts for the distribution of alkylphenols and possibly other hydroxylated polar constituents found in crude oils. These acid catalysed hydroxylation reactions are suggested to take place in the source rock during petroleum formation.

Partial mass chromatograms showing similar distributions of alkylphenols produced in laboratory hydroxylation reactions to those in crude oil

Reconstruction of petroleum migration pathways

In addition to alkylphenols, we are studying the distributions of alkylcarbazoles which are nitrogen containing organic compounds. Little is known about their origin and behaviour in geological samples. Preliminary work suggests that by combining data from the two compound types, detailed information on migration pathways may be revealed. Hydrocarbon accumulation processes in the Kendrew Trough system of the Dampier Sub-basin were investigated using phenol and carbazole abundance in crude oils. Crude oils were placed into two groups based on the relationship between phenols and carbazole. High phenol and carbazole concentrations were observed in crude oils that were close to the major depocentre areas, which we suggest is related to relatively short migration distances. The results indicate that these parameters are useful for reconstructing migration pathways and distinguishing different crude oil sources.

Personnel

B. van Aarssen, T. Bastow, R. Alexander, R. Kagi

Funding

Australian Petroleum CRC, MERIWA