Nigel J. Russell

Petroleum source rock assessment in non-marine sequences: pyrolysis and petrographic analysis of Australian coals and carbonaceous shales

A series of Australian coals and terrestrial sediments ranging in age from Permian through tertiary have been analyzed to assess their petroleum source character and the suitability of various techniques for assessment of source rock potential in non-marine sequences. The procedures used include organic petrography, Rock-Eval pyrolysis, elemental analysis and quantitative pyrolysis-gas chromatography. The latter procedure was used to assess the potential yield of paraffins which is critical to the assessment of most non-marine source rocks. Principal components analysis was used to assist in the analysis of the data. Although the petroleum potential of the samples follows the broad trends in petrographic composition established for Australian coals, i.e. relative proportions of vitrinite, inertinite and liptinite, there is much variation which cannot be explained petrographically at the maceral group level. Further, pyrolytic hydrocarbon yield is not related to overall elemental composition below an atomic H/C ratio of 1.0. The yield of phenols in flash pyrolysis is related to depositional setting as well as degree of maturation. The yield and carbon number distribution of normal hydrocarbons in flash pyrolysis varied widely depending on the age, nature and amount of liptinite macerals particularly in samples with Hydrogen Indices below 300. Liptinite-poor (< 10%) samples may yield significant amounts of hydrocarbons, but typically they have a low wax content. Sporinite-rich and liptodetrinite-rich samples give lower yields of normal hydrocarbons. These are predominantly of lower molecular weight. Suberinite and to a lesser extent cutinite are associated with high yields of waxy normal hydrocarbons, but some samples with high yields did not contain large amounts of these maceral. The correlation of Tmax to vitrinite reflectance varies with petrographic composition. The results have implications for the way source rock analyses are conducted and interpreted in non-marine sequences.

Fluorescence alteration and the suppression of vitrinite reflectance

Abstract Vitrinite reflectance is a highly important thermal maturity indicator in petroleum exploration, but there are a number of problems in its successful application which are basically the consequence of it being a single parameter technique. Fluorescence alteration of macerals, which can be conveniently measured with the laser Raman microprobe, is a multi-parameter technique which can be used to overcome some of these limitations. On a fluorescence alteration diagram most vitrinite plots on, or close to, a line which may be called the “normal” vitrinite line. Fluorescence alteration data for a suite of randomly selected macerals from coal, or dispersed organic matter, plot along a curve which cuts the “normal” vitrinite line at the equivalent vitrinite reflectance of the sample, as determined by calibration againsta suite of reference coals. The technique posseses a high degree of objectivity and can be employed to determine the equivalent vitrinite reflectance of samples in which the vitrinite is difficult to identify, or even absent. Perhydrous vitrinites, with suppressed vitrinite reflectance, are readily recognized as they plot in a field laterally displaced with respect to the “normal” vitrinite line. The method is exemplified by a study of coals from the Greta and Pelton seams, Sydney Basin, which provides a classic example of vitrinite reflectance suppression, and is further illustrated by a study of the Dampier #1 well from the North West Shelf of Australia which contains both perhydrous macerals and dispersed organic matter in which vitrinite is difficult to identify.

Exploitation of relaxation in cross-polarization nuclear magnetic resonance spectroscopy of fossil fuels

Abstract The judicious choice of dipolar dephasing times or carbon magnetization holding times has been shown to improve resolution in solid state nuclear magnetic resonance (NMR) spectra of complex materials. Signals from protonated and alkylated aromatic carbons are reduced to enhance resolution of aromatic oxygenated groups. Rapidly rotating methyl groups can be resolved from other aliphatic carbon types. These techniques were used to investigate the structure of a brown coal, xylite fractions of a brown coal, a bituminous coal, an oil shale and a solvent-refined coal. The results allow estimates of the fraction of aromatic carbon that is protonated in coal to be made, and demonstrate that methyl groups in coal rotate rapidly at room temperature.

Gelification of victorian tertiary soft brown coal wood. II. Changes in chemical structure associated with variation in the degree of gelification

Abstract The gross chemical structures of xylites and gelified soft brown coal woods, Latrobe Valley, Victoria, Australia, as determined by solid state nuclear magnetic resonance spectroscopy, are compared with those of present-day wood-derived materials prepared from an angiosperm, Eucalyptus regnans, and a gymnosperm (conifer), Pinus radiata. Also examined are the changes in the gross chemical structures of soft brown coal woods with increase in their degree of gelification and the relationship between these changes and variations in their chemical composition and microscopic appearance. The Victorian xylites exhibit greater affinities with the present-day gymnosperm than the present-day angiosperm. The progressive removal of cellulose with increasing degree of gelification can be equated with an increase in huminite reflectance, elimination of humotelinite autofluorescence and changes in the relative proportions of the humotelinite submacerals. The lignin structure of xylite is also modified during the gelification process, including the progressive loss of methoxyl groups and evidence of minor oxidation.

The nature of olefins and carboxyl groups in an Australian brown coal resin

The chemical structure of the resin from an Australian soft brown coal (Yallourn) has been investigated by cross-polarization nuclear magnetic resonance spectroscopy with magic angle spinning (13C CP MAS NMR). Some additional solution 1H and 13C data were also obtained. Solid-state experiments were performed with and without a delay period before data acquisition. The resulting free induction decays were Fourier transformed with respect to acquisition time and delay period to produce two-dimensional solid-state spectra. Assignments made from the spectra clearly demonstrate that the gross chemical structure of the Yallourn resin is best described as a polymerized diterpenoid with one axial carboxylic group and two double bonds. One double bond is trisubstituted, the other is monosubstituted. After consideration of various mechanisms for polymerization of diterpenoid units during biogenesis and coalification, it was concluded that polymerization occurs at the C15 carbon atoms in the diterpenoids without cyclization of the methylene units at C8.

Preliminary studies on the aromaticity of Australian coals: Solid state n.m.r. techniques

Abstract The aromaticities of samples from nine Australian coal seams, including pairs of hand-picked vitrains and durains, have been determined by 13 C cross-polarization n.m.r. spectroscopy with magic angle sample spinning. The results clearly show that the aromaticity ( f a ) of the coals increases with increase in vitrinite reflectance and carbon content and decrease in atomic H/C ratio. For a given coal seam, durain (inertinite-rich coal) has a higher f a value than vitrain (vitrinite-tich coal). The trends for carbon content and atomic H/C are in good agreement with results from North American coals, although the aromaticities of Australian coals obtained in this study appear to be slightly lower than some of those reported for North American coals of similar carbon content.

Microscopic observations of the swelling of a high-volatile bituminous coal in response to organic solvent

Abstract The swelling behaviour of individual coal macerals in response to solvents is thought to be important since it represents an early stage in the disintegration of the coal, which is, in turn, of fundamental importance to coal hydrogenation at elevated temperatures. Therefore, a detailed incident-light microscope study of solvent-treated, polished coal surfaces, involving a new edge-on mode of observation, was undertaken in order to observe the way in which solvents interact with the different coal macerals. This study was carried out on blocks of Bayswater Seam coal, using tetralin, pyridine, and 1:3 maleic anhydride-xylene solutions at temperatures near their respective boiling points. The degree of swelling of the polished coal surface depends on the nature of the organic solvent and the individual coal macerals. Vitrinite and, in some instances, low-reflectance semifusinite exhibit varying degrees of swelling in response to the solvent treatment; whereas exinite and the majority of the inertinite macerals appear to be unaffected by the solvents. Within the vitrinite group the lower-reflectance sub-macerals exhibit the greater degree of swelling. At temperatures of less than 200 °C the ability of the solvents to produce swelling in the coal decreases in the order pyridine → 1:3 maleic anhydride-xylene → tetralin.

Characterization by pyrolysis-gas chromatography-mass spectrometry of the insoluble organic residues derived from the hydrogenation of Tasmanites sp. oil shale

Abstract The insoluble organic residues from the hydrogenation of Tasmanites sp. oil shale have been characterized by Curie point pyrolysis combined with gas chromatography and computerized gas chromatography-mass spectrometry. The resulting pyrograms show that very little, if any, hydrogenation of the residues occurs. Rather, the initial step in the sequence is pyrolysis of the residue followed by hydrogenation of the liquid products. Major compounds identified from the pyrograms of the residues include alkene/alkane doublets, mixtures of diterpenoids and mono- di- and triaromatic compounds. Changes in the distribution of these compounds with changes in reaction conditions are discussed.

Some aspects of the behaviour of tin(II) chloride during coal hydrogenation in the absence of a solvent

Abstract In this application of optical and electron microscopy to the study of catalytic hydrogenation of coal, the coal is regarded as a stationary phase and the catalyst and hydrogen as mobile entities. Sampling was carried out at various stages, in the 320–474 °C temperature range, of the catalytic hydrogenation of a high-volatile bituminous coal (Bayswater seam, New South Wales, Australia) with tin(II) chloride in the absence of a solvent. The behaviour of coal macerals during hydrogenation, the mode of occurrence, morphology and composition of the catalyst, and the distribution of the elements of interest (Sn, CI, Fe, S) in hydrogenated vitrinite are described. The study has shown that both tin and chlorine can enter the coal at the very earliest stages of hydrogenation. Deep penetration of the coal by tin and chlorine takes place with progressive hydrogenation; the extent of the catalyst penetration coincides with the optically-defined hydrogenation zone. Discrete catalyst grains are confined to the hydrogenated zone; these grains do not occur at the active front of hydrogenation. Tin(II) sulphide is the product of the scavenging of sulphur by tin and is the predominant form of the catalyst after the onset of mesophase formation.

Gelification of Victorian Tertiary soft brown coal wood. I: Relationship between chemical composition and microscopic appearance and variation in the degree of gelification

Abstract The relationship between chemical composition and microscopic appearance of present-day wood-derived materials and Victorian xylites and gelified soft brown coal woods, Latrobe Valley, Australia, is discussed. The present-day wood-derived material consists of milled wood and lignin and holocellulose fractions prepared from an angiosperm, Eucalyptus regnans and a gymnosperm, Pinus radiata . The xylites and least gelified soft brown coal woods resemble the P. radiata lignin fraction; the latter contains residual cellulose. The atomic H/C ratio was found to be a useful guide to the degree of gelification. Increase in the degree of gelification was accompanied not only by an increase in the total huminite reflectance, but also by an increase in the reflectance of the individual huminite submacerals. The loss of hymotelinite autofluorescence under ultraviolet and blue light excitation with increase in the degree of gelification of Victorian soft brown coal woods was ascribed primarily to the elimination of cellulose and, possibly, modification of the lignin structure of xylite.