LmPy-GCMSMS and Other Alternative Methodologies in the Screening for Source Rocks
Pyrolysis gas chromatography‐mass spectrometry (Py‐GCMS) is a hyphenated analytical technique applied using a Pyrolyzer (Laser Source), Microscope, Gas Chromatograph (GC), and Mass Spectrometer (MS). Pyrolysis has been used extensively over the last 20–30 years as an analytical technique, in which large molecules are degraded into smaller volatiles species using thermal energy only (Hanson et al., 1975). For improvement of the analytical process, this technique uses the chromatographic information to determine the composition or structure of the original sample (Sobeih et al., 2008). Gas chromatography‐mass spectrometry (GC‐MS) detection provides molecular analysis of gaseous species and its combination with the laser system has resulted in a relatively new technique termed Laser Micropyrolysis‐Gas Chromatography–Mass Spectrometry (LmPy‐GCMS) (Greenwood et al., 1996, 1998). Among pyrolysis techniques, laser micropyrolysis has relatively succeeded in providing important molecular data on organic fossils such as coals, source rocks, oil shales and kerogen, and has also been useful in assessing the oil‐proneness and maturity of maceral materials (Greenwood et al., 1993; Stout and Lin, 1992; Stout, 1993; Vanderborgh and Jones, 1983; Yoshioka and Takeda, 2004; Silva et al., 2016). Previous works showed studies with laser micropyrolysis were primarily focused on instrumental development and the authors listed a number of factors that could explain this setting as: the sensitivity limitations of chromatographic technologies required for small product concentrations; the interdisciplinary skills needed; the financial expense of the different instruments; the difficulties involved with interfacing these instruments; the lack of understanding of the interactions between laser and material; and the issue that not all samples are compatible with laser radiation to produce pyrolysis products (see Sobeih et al., 2008). Nevertheless, the LmPy‐GC‐MS method has been successfully applied to different organic components. For example, Greenwood et al. (1998) demonstrated the credibility in the LmPy‐GCMS through the analysis of micro‐sized quantities of various organic fossils. Their results were confirmed by the favorable comparison from the laser derived molecular data to corresponding data obtained from more traditional methods. Arouri et al. (1999) performed laser pyrolysis on small populations (≤10) of acritarch specimens and showed that laser pyrolysates reflect a significant aliphatic and aromatic content of the studied acritarchs, a result consistent with the thermal desorption‐mass spectrometry data exposed in the same paper. Greenwood et al. (2000) studied the hydrocarbon composition of a Tasmanite oil shale and isolated Tasmanites that were separately investigated by LmPy‐GCMS and concluded that the very similar tricyclic content of both samples strongly supports the proposal of an inherent relationship between the Tasmanites and tricyclic terpenoid production. Meruva et al. (2004) describes the design, construction and applications of UV laser pyrolysis‐GC/TOF‐ MS for characterization of synthetic polymer samples, observing that laser pyrolysis requires little or no sample preparation and reduces sample size requirements. Jacob et al. (2007) provided LmPy‐GCMS on individual and well‐preserved chitinozoan specimens extracted from Silurian marine rocks. They observed that organic structures of chitinozoans appear to be a kerogen network dominated by aromatic units with few aliphatic groups. Saundouk‐Lincke et al., (2013) compared micro‐ and macroscale spectroscopic and pyrolysis methods demonstrating that both micro‐Fourier transform infrared (μ‐FTIR) spectroscopy FTIR analysis and LmPy‐ GCMS provide similar trends with maturation, whereas the results from Curie Point‐Py showed wide differences, especially at higher stages of maturity. They concluded that both IR spectroscopy and LmPy‐ GCMS are suitable for studying the alteration of palynomorphs during maturation, whereas for immature materials Curie Point‐Py–GC/MS appears to be a more suitable method as the applied temperature can be adjusted much more accurately (Saundouk‐Lincke et al., 2014). Silva et al. (2016) used LmPy‐GCMSMS to compare the chemical composition of both Botryococcus and Gloeocapsomorpha prisca microfossils and to evaluate the similarities and differences between their chemical compositions, once the chemical structure of these microorganisms has long been a topic of debate in geochemistry. All these studies show that laser pyrolysis has a high potential to improve our understanding of the organic composition of heterogeneous materials and isolated organic‐walled microfossils, allowing to individually analyzing, on an isolated way, very small components within complex mixtures. In Palynofacies and Organic Facies Laboratory (LAFO‐UFRJ), the micropyrolysis system refers to a laser and an optical device; a sample chamber and cold trap; and a gas chromatographer coupled with triple quadrupole mass spectrometer (LmPy‐GCMS) to separate and detail the composition of molecular pyrolysis products. This system was assembled exclusively for LAFO/UFRJ by CSIRO Division of Petroleum Resources (Sydney, Australia) with financial support from PETROBRAS/Brazil.
AAPG Datapages/Search and Discovery Article #90349 © 2019 AAPG Hedberg Conference, The Evolution of Petroleum Systems Analysis: Changing of the Guard from Late Mature Experts to Peak Generating Staff, Houston, Texas, March 4-6, 2019