Vitrinite reflectivity

To assess potential yield and maturity of source rocks and classify those according to their vitrinite reflectance . 

Vitrinite Reflectance. The amount of light reflected from a poHshed plane surface of a coal particle under specified illumination conditions increases with the aromaticity of the sample and the rank of the coal or maceral. Precise measurements of reflectance, usually expressed as a percentage, ate used as an indication of coal rank. 

Table 2. Vitrinite Reflectance Limits, Taken in Oil, and ASTM Coal Rank Classes ...

Seam correlations, measurements of rank and geologic history, interpretation of petroleum (qv) formation with coal deposits, prediction of coke properties, and detection of coal oxidation can be deterrnined from petrographic analysis. Constituents of seams can be observed over considerable distances, permitting the correlation of seam profiles in coal basins. Measurements of vitrinite reflectance within a seam permit mapping of variations in thermal and tectonic histories. Figure 2 indicates the relationship of vitrinite reflectance to maximum temperatures and effective heating time in the seam (11,15). 

Recent work has suggested that the coals of the Illinois Basin were never buried deeper than about 1500 m. (44), compared with an estimated 3000 m. or more for the coals of western Pennsylvania in the Eastern province. Presumably as a consequence, the coals of the Interior province tend to show low values of vitrinite reflectance and high values of moisture-holding capacity relative to coals of other areas of apparently similar rank (45). 

Low volatile bituminous coal rank and heating values, 6 726t vitrinite reflectance limits and ASTM coal rank classes, 6 708t Low volatile bituminous coal grade (U.S.), 6 713t... 

The mobile phase and the nature of H-donor and non-donor solvents all have a profound influence on primary conversions. In contrast, distillate or oil yields often correlate with parameters reflecting the aliphaticity of coals (H/C ratio -decreasing vitrinite reflectance - CHj content - Z), better correlations being achieved for low-rank coals if yields are expressed on a free" basis... 

Coal Particle Unchanged- -with pore development -no softening, no vesiculation little change in vitrinite reflectance, -softening, some vesiculation but recognisable as coal. 

Such correlations have important bearings on the current level of understanding regarding the mechanisms of pyrolysis devolatilisation and char formation. Furthermore, standard forms of analyses are subject to oxidation or weathering effects and this study demonstrates that correlations between levels of unbumt carbon and vitrinite reflectance (33) maybe potentially misleading unless the affects of oxidation or weathering are considered. 

None of the lignocellulosic plant tissues in coal balls has been altered to vitrinite in any of the various European and American coal balls I have examined. It would be very interesting to know the source of Dr. Teichmuller s coal ball vitrinite reflectances. I believe they must refer to streaks of unmineralized peat which can be found associated between centers of coal ball mineralization which had been compressed and coalified rather than actually petrified. None of the plant material within coal balls I have examined can be taken as having any bearing on metamorphism or on the rank of the coal. 

The components analysis containing vitrinite reflectance is reported in Table IX. Reflectance is split into three components, loading most strongly on component 1. The aromatic bands represented by that at 750 cm-1 show complete dependency with reflect-... 

The mean maximum reflectance of vitrinite was determined in oil (ca. 1.517 index of refraction) and in 546-nm wavelength green light. A photomultiplier photometer was used to measure vitrinite reflectance. Two glass standards were used to calibrate the equipment. A Leitz MPV2 microscope photometer was used. The reflectance values were determined as designated in ASTM D2798-85 (2 5). Twenty-five vitrinite reflectance values were determined for the Rasa coal. 

The upper Cretaceous Jurf ed Darawish oil shale (thickness ca. 120m 45m-165m depth) in the Ghareb Formation is a calcareous, bituminous marl (commercially termed oil shale), which is located 130 km south of Amman, Jordan (14). The organic matter in this sequence is thermally immature ("vitrinite" reflectance = 0.28-0.31 % L. Buxton, pers. comm.)... 

Figure 9. Relationship between the thiophene ratio, TR, and Rock-Eval Tmax f°r samples °f varying kerogen type. NB. All samples are immature with respect to oil generation (i.e. vitrinite reflectance, R0 < 0.5%).

Figure 10. FPD chromatograms from flash pyrolysis of Mahakam coals. Sample depth, vitrinite reflectance, Rock-Eval Tmax, hydrogen index (HI) and the thiophene ratio (TR) are shown. Peak identifications are given in Table V.

The following organisations are thanked for their kind donation of samples Institute Francais du Petrole, British Petroleum, Norsk Hydro. We are grateful to the analytical departments at Bristol University and at BP Research Centre for the elemental analyses. Dr. A. Pepper (BP) is acknowledged for provision of burial history information for the Monterey Fm. kerogens. ll Buxton (Geolab Nor) is thanked for selected TOC determinations. Dr. J.M. Jones (University of Newcastle) is thanked for vitrinite reflectance analyses. We thank Dr. A.K. Burnham for supplementary kinetic analyses. W. Pool is thanked for technical assistance. Drs. K. Peters, W.L. Orr and C.M. White are thanked for critical reviews. 

Six vitrinite samples from the Lower Kittaning seam were hand-picked to represent a wide range of vitrinite reflectance. These samples exhibited a minimum of 97% vitrinite and were used without further purification. Samples were supplied by Professor Alan Davis of Pennsylvania State University. 

---