--> Micro-Ablation: A New Technique for Removing Hydrocarbon Contaminants and Facilitating Biomarker Analyses of Cuttings

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Micro-Ablation: A New Technique for Removing Hydrocarbon Contaminants and Facilitating Biomarker Analyses of Cuttings

Abstract

Biomarkers and other hydrocarbons from potential source rocks act as important geochemical proxies in petroleum exploration efforts. However, for biomarker-based petroleum studies to be accurate, acquisition of reliable data and proof of their syngeneity is essential. Unfortunately, contamination of geological samples with petroleum products during drilling, storage and sampling can be particularly problematic as these hydrocarbons can over-print an original indigenous biomarker profile (e.g. Brocks et al. 2008). In order to obtain an indigenous hydrocarbon signal, a number of methods have been developed to remove contaminants. One particular method, the “micro-ablation technique”, allows for the sub-millimetre removal of layers of contaminated surfaces from pieces of sedimentary rock that are too small or irregularly shaped to be trimmed using a saw. The process involves the use of a vibratory tumbler that removes exterior rock surfaces with the help of ceramic polishing media and silicon carbide as an abrasive. Previous work by Jarrett et al. (2013) has demonstrated the effectiveness of this technique in either removing surface hydrocarbon contaminants or help in quantitatively evaluating the migration of these allochtonous hydrocarbons into a rock sample. While the micro-ablation technique has been successfully applied to rock samples derived from whole cores, it has never been tested for small rock sizes like cuttings and sidewall cores. This is unfortunate, since the latter types of cores are derived from the most frequently used drilling techniques in the petroleum industry. They are commercially cheaper to obtain than whole cores yet provide significant insight into the subsurface geology of petroleum basins. However, cuttings are not recommended for biomarker analyses because they are most readily affected by flushing with oil- and water-based drilling muds and lubricants. We recently extended the micro-ablation technique to cuttings. We will demonstrate the success of this technique in physically removing contaminated surfaces from cuttings less than 1 cm in diameter and show how the resulting biomarker patterns can be interpreted. Ultimately, this technique will reveal unprecedented insights into previously inaccessible biomarker data for petroleum exploration efforts. References: Brocks J.J., et al. 2008. Geochimica et Cosmochimica Acta, v. 72, 871–888. Jarrett A.J.M., et al. 2013. Organic Geochemistry, v. 61, 57–65.