Comparison of hydrocarbon compositions in a sequence of humic coals, cannel coals and oil shales from the Pictou Coalfield, Nova Scotia

Thirty oil shale, cannel coal and humic coal samples from die Pennsylvanian Stellarton Group, Nova Scotia, Canada have been investigated in this study by means of organic geochemical methods including gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). Hydrocarbon compositions of the solvent extracts were found to vary significantly with lithology and facies. Analysis of the saturated hydrocarbon fractions revealed that the relative amounts of long-chain alkanes (>C20) compared to those of short-chain alkanes (<C20) are higher in the humic coal than in the cannel coal and oil shale samples. Moreover, the humic coal is characterized by the presence of homodrimane as the dominant bicyclic alkane. In the oil shale and cannel coal samples, on the other hand, C15-bicyclancs are present as major sesquiterpenoid hydrocarbons. Compounds such as biphenyl, dibenzofuran, fluorene and their mono-mediylated and di-metfiylated homologues were shown to occur almost exclusively in the aromatic hydrocarbon fractions of the humic coal samples. Presumably, these compounds are products of die degradation of lignin during diagenesis. The bitumen compositions of cannel coal and oil shale samples are quite similar. RÉSUMÉ Trente échantillons de schiste bitumineux, de charbon de spores et pollens, et de charbon humique provenant du Groupe de Stellarton (Pennsylvanien de la Nouvelle-Écosse, Canada) ont été analysés dans cette étude à l'aide de méthodes de géochimie organique comprenant la chromatographic en phase gazeuse (GC) et le couplage chromatographic en phase gazeuse -spectrométrie de masse (GC/MS). On constata que les compositions d'hydrocarbures des extraits en solvent varient fortement selon la lithologie et le faciès. Une analyse des fractions à hydrocarbures satures révèla que la proportion des alcanes à longue chaine (>C20) par rapport aux alcanes à chaine courte (<C20) est plus élevée dans le charbon humique que dans les échantillons de charbon de spores et pollens et de schiste bitumineux. De plus, le charbon humique est caractérisé par la présence d'homodrimane comme alcane bicyclique principal. Par centre, dans les échantillons de schiste bitumineux et de charbon de spores et pollens, on note la présence de C15j-bicyclanes comme hydrocarbures sesquiterpénoiides majeurs. Certains composes, tels le biphényle, le dibenzofurane, le fluorène el leurs homologues mono- et diméthylés, se retrouvent presqu'exclusivement dans les fractions à hydrocarbures aromatiques des échantillons de charbon humique. Ces composés serai ent leproduit de la dégradation de la lignine durant ladiagenèse. Les compositions bituminiques des échantillons de charbon de spores et pollens et des schiste bitumineux se ressemblent beaucoup. [Traduit par le journal

Application of reflectance parameters in the estimation of the structural order of coals and carbonaceous materials. Precision and bias of measurements derived from the ICCP structural working group

Optical reflectance of vitrinite is one of the fundamental physical properties that have been used for the study of coal and carbonaceous materials. Organic matter in coals and carbonaceous matter consists mainly of aromatic lamellae, whose dimensions and spatial orientation define its internal structure. Various reflectance parameters describe well the average degree of order of the molecular structure of organic matter. Moreover, reflectance parameters are numerical values which characterize the samples unambiguously, facilitating the comparison of the optical properties of different carbonaceous materials as well as comparison between optical parameters and other physical or chemical factors. The focus of this study is the evaluation of the precision and bias of reflectance measurements (R and R) performed by various analysts in different laboratories in order to check the applicability of reflectance parameters to the estimation of the structural order of coals and carbonaceous materials. Additionally, it was desirable to compare reflectance parameters with other parameters obtained by different analytical methods able to provide structural information. The consistency and repeatability of the reflectance measurements obtained by different participants turned out to enable the drawing of similar conclusions regarding the structural transformation of anthracite during heating. Good correlations were found between the reflectance parameters studied and structural factors obtained by comparative methods. The reflectance parameters examined proved to be very sensitive to any changes of the structural order of coals and carbonaceous materials and seem to be a perfect complement to structural studies made by X-ray diffraction or Raman spectroscopy

Organic petrology and rock-eval studies on oil shales from the Lower Carboniferous Rocky Brook Formation, Western Newfloundland

journal articleNine samples of oil shale from the Carboniferous Rocky Brook Formation along Rocky Brook in western Newfoundland were studied by incident light microscopy and geochemical analysis (Rock-Eval pyrolysis) to determine the maceral components, geochemical type, and maturation level of the kerogen fraction, and to determine the character and potential yield of the pyrolyzate. These oil shale beds are Type I lacustrine lamosites dominated by the maceral lamalginite. Optical properties indicate low to moderate thermal maturation but, as shown by geochemical analyses, the beds are immature and hydrocar- bons have not yet been generated. This relationship is characteristic of Type I deposits. The laminated strata generally contain greater than 5% organic carbon and yield upon pyrolysis sufficient petroleum product to be of economic interest; however, known bed thicknesses are too low to be currently attractive. More massive organic-rich beds may contain less than 4% organic carbon; the yield potential in these beds is severely restricted by an apparent mineral-matrix effect

Petrology, Rock-Eval and facies analyses of the McLeod coal seam and associated beds, Pictou Coalfield, Nova Scotia, Canada

Coals, caimel coals and oil shales of the McLeod sequence from two boreholes in the Pictou Coalfield, Nova Scotia were analysed using methods of organic petrology and organic geochemistry. Petrographic composition was determined by maceral and microlithotype analyses. Within the McLeod coal seam, varying amounts of alginite, vitrinite, inertinite, and mineral matter indicate significant changes in the environment of deposition. High amounts of lamalginite and minerals, i.e., clay minerals and pyrite at the base and top of the seam indicate a lirnnic depositional environment, whereas much dryer conditions are indicated for the middle portion of the seam by better tissue preservation, typical for a wet forest type of swamp. This is confirmed also by results from microlithotype analyses. In the oil shales the predominant maceral is alginite. Coals, cannel coals and oil shales vary significantly in TOC values and hydrocarbon potentials. Parameters such as hydrogen and oxygen indices and hydrocarbon potentials are in good agreement with results from petrographic analyses. Methods of organic petrology and organic geochemistry define distinct types of organic matter in coals, cannel coals and oil shales which can be related to facies changes and environments of deposition. From the preliminary results it appears that these methods also can be applied regionally for stratigraphic correlations within sequences of rapid facies changes. RÉSUMÉ Des charbons, des charbons de spores et pollens, ainsi que des schistes bitumineux appartenant à la série de McLeod et provenant de deux sondages dans le bassin houiller de Pictou (Nouvelle-Écosse) furent analyses à l'aide de méthodes de pérologie et de géochimie organiques. On détermina la composition pétrographique grace à une analyse des macévaux et des microlithotypes. La variation des teneurs en alginite, vitrinite, inertinite et en composants min&aux au sein du filon charbormeux de McLeod témoigne de changements majeurs dans le milieu de dépôt. Un milieu de dépôt limnique est indiqué par des teneurs élevées en lamalginite et en minévaux, i.e. minéraux argileux et pyrite, tant à la base qu'au sommet du filon. En revanche, une meilleure conservation des tissus, typique des marécages de foret humide, trahit des conditions beaucoup plus seches pour la portion centrale du filon. Les resultats de analyses de microlithotype confirment cet état de chose. L'alginite est le macéral prédominant dans les schistes bitumineux. Les charbons, les charbons de spores et pollens, ainsi que les schistes bitumineux varient fortement aux plans du COT et du potentiel pétroligène. Certains paramétres, comme les indices d'hydrogene et d'oxygène et les potentiels pétroligènes, confortent les résultats obtenus grace aux analyses pétrographiques. Au sein des charbons, charbons de spores et pollens, et schistes bitumineux, les méthodes de la pétrologie et de la géochimie organiques détuiissent des types distincts de matiere organique qui peuvent être liés aux changements de faciès et aux milieux de dépôt. À partir de ces résultats préliminaires, il semble qu'on puisse utiliser ces méthodes à une échelle régionale pour nialiser des corrélations stratigraphiques à l’intérieur de séries montrant des changements rapides de faciès. [Traduit par le journal