REFLECTANCE RETARDATION (SUPPRESSION) AND SOURCE ROCK PROPERTIES RELATED TO HYDROGEN‐ENRICHED VITRINITE IN MIDDLE JURASSIC COALS, DANISH NORTH SEA

Middle Jurassic high volatile bituminous A coals from the Danish North Sea may yield vitrinite reflectance values retarded by 0.10–0.14 %Rr The coals are low in liptinite content, and the reflectance retardation is related to the vitrinite composition. Vitrain (assumed to be pure vitrinite) was hand‐picked from eight samples and characterised by means of element analysis, Fourier Transform infrared spectroscopy and Rock‐Eval pyrolysis. In contrast to the vitrinite from samples yielding “true” reflectance values, the vitrinite from three of the samples yielding retarded reflectances is perhydrous in nature (5.57–5.79 wt‐% (d.a.f.) H) and has H/C atomic ratios of 0.80–0.83. Vitrinite from another reflectance‐retarded sample is enriched in sulphur. The hydrogen enrichment is inherited from oxygen‐deficient, waterlogged and marine‐influenced conditions in the precursor mires. FTIR spectra demonstrate that the perhydrous vitrinites have a lower aromaticity as measured by aromatic hydrogen vibrations in the region 900–700 cm‐1 compared to the “normal” vitrinites. This suggests a reduced maturation rate of the hydrogen‐enriched vitrinite. S1(Vitr), S2(vitr) and HIvitr values from the vitrinite concentrates indicate that the vitrinite is a significant contributor to the overall generative potential; this is particularly the case for the perhydrous vitrinite. Activation energies for the vitrinites are centred at 260 and 268 kJ/mole. It is not possible to detect a measurable difference in Ea between the perhydrous and “normal” vitrinites. This may suggest more‐or‐less similar generation characteristics, or it may indicate that Rock‐Eval kinetics do not replicate Nature in this regard.

[1]  P. Rosenberg,et al.  Petroleum potential and depositional environments of Middle Jurassic coals and non-marine deposits, Danish Central Graben, with special reference to the Søgne Basin , 1998 .

[2]  J. Newman,et al.  HYDROCARBON SOURCE POTENTIAL AND MATURATION IN EOCENE NEW ZEALAND VITRINITE‐RICH COALS , 1997 .

[3]  H. Petersen,et al.  Organic facies development within Middle Jurassic coal seams, Danish Central Graben, and evidence for relative sea-level control on peat accumulation in a coastal plain environment , 1996 .

[4]  P. Landais,et al.  Coalification stages from confined pyrolysis of an immature humic coal , 1996 .

[5]  Wuu-Liang Huang.  Experimental study of vitrinite maturation : effects of temperature, time, pressure, water, and hydrogen index , 1996 .

[6]  P. Rosenberg,et al.  Organic Geochemistry in Relation to the Depositional Environments of Middle Jurassic Coal Seams, Danish Central Graben, and Implications for Hydrocarbon Generative Potential , 1996 .

[7]  R. Bustin.  Vitrinite Reflectance as a Maturity Parameter, Applications and Limitations Edited by P. K. Mukhopadhyay and W. G. Dow; American Chemical Society Symposium Series 570; American Chemical Society: Washington, DC, 1994; 294 pp. , 1996 .

[8]  M. Mastalerz.  Application of reflectance micro-Fourier transform infrared spectrometry in studying coal macerals: comparison with other Fourier transform infrared techniques , 1995 .

[9]  T. Gentzis,et al.  Reflectance Suppression in Some Cretaceous Coals from Alberta, Canada , 1994 .

[10]  K. Pratt,et al.  A plant tissue origin for ulminites A and B in Saskatchewan lignites and implications for Ro , 1994 .

[11]  F. Laggoun‐Défarge,et al.  Influence of Resinite on Huminite Properties , 1994 .

[12]  A. Scott,et al.  Introduction to the petrology and infrared spectra of Shanxi coals, People's Republic of China , 1994 .

[13]  T. Gentzis,et al.  Petrological and chemical characteristics of liptinite-rich coals from Alberta, Canada , 1994 .

[14]  Van Krevelen,et al.  Coal: Typology - Physics - Chemistry - Constitution , 1993 .

[15]  M. Mastalerz,et al.  Variation in chemistry of vitrinite and semifusinite as a function of associated inertinite content , 1993 .

[16]  P. Johannessen,et al.  Middle to Late Jurassic basin evolution and sandstone reservoir distribution in the Danish Central Trough , 1993 .

[17]  Hao Fang,et al.  THE CAUSE AND MECHANISM OF VITRINITE REFLECTANCE ANOMALIES , 1992 .

[18]  C. Diessel.  Coal Bearing Depositional Systems , 1992 .

[19]  A. Raymond,et al.  Anomalies in vitrinite reflectance gradients , 1991 .

[20]  L. Snowdon,et al.  Hydrocarbon Generation Kinetics and Thermal Modelling, Beaufort-Mackenzie Basin , 1990 .

[21]  W. V. Bronswijk,et al.  Source and heating rate effects upon maturity parameters based on ratios of 24-ethylcholestane diastereomers , 1989 .

[22]  P. Ungerer,et al.  Thermal History of Sedimentary Basins, Maturation Indices, and Kinetics of Oil and Gas Generation , 1987 .

[23]  L. C. Price,et al.  SUPPRESSION OF VITRINITE REFLECTANCE IN AMORPHOUS RICH KEROGEN --A MAJOR UNRECOGNIZED PROBLEM , 1985 .

[24]  P. Painter,et al.  Relationships between the organic structure of vitrinite and selected parameters of coalification as indicated by Fourier transform IR spectra , 1984 .

[25]  W. Kalkreuth.  Rank and Petrographic Composition of Selected Jurassic - Lower Cretaceous Coals of British Columbia, Canada , 1982 .

[26]  J. Newman,et al.  Reflectance anomalies in Pike River coals: Evidence of variability in vitrinite type, with implications for maturation studies and “Suggate rank” , 1982 .

[27]  R. W. Snyder,et al.  Concerning the Application of FT-IR to the Study of Coal: A Critical Assessment of Band Assignments and the Application of Spectral Analysis Programs , 1981 .

[28]  A. Cook,et al.  Influence of alginite on the reflectance of vitrinite from Joadja, NSW, and some other coals and oil shales containing alginite , 1980 .

[29]  G. Eglinton.  Petroleum geochemistry and geology , 1980 .

[30]  J. K. Brown.  The infrared spectra of coals , 1955 .