Vitrinite reflectance values

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. 

Figure 7. CP /MAS spectra of vitrinite samples from the Lower Kittanning Seam. The spectra represent changes that occur with rank progression. V refers to vitrinite reflectance values.

Figure 15. Arsenic concentrations in coals of the Black Warrior basin, Alabama. Shaded areas show the extent of coalfields of Alabama. The proportionally sized symbols. show the content of arsenic in coal samples analyzed by the USGS. Some symbols that plot inside each other are from the same core or coal face. The break points for the symbol groups were calculated using the natural breaks algorithm in the computer program Arcview . Dashed lines are contours of vitrinite reflectance data from coals. We are presently evaluating whether the tack of correspondence of high arsenic content with high vitrinite reflectance values is an artifact due to low sample density or reflects an actual trend in the data.

Fig. 4.15 A van Krevelen plot showing the evolutionary trends of the main kerogen types (shaded bands after Behar Vandenbroucke 1987) and most coals (between solid lines after Killops etal. 1998). With increasing maturity kerogens follow a path towards the origin, as shown for the low/high-H coals boundary.The main hydrocarbon-generation zones are shown, with their approximate rank boundaries (as vitrinite reflectance values, %Ro), together with the effect of loss of various volatiles from different kerogen compositions (CH2 = oil). Points represent the composition of kerogens in Fig.4.14.

Source rock maturity. In a study of the diagenesis and burial history of the Lower Cretaceous Travis Peak Formation in eastern Texas, Dutton (1987) reported measured vitrinite reflectance values for Travis Peak shales generally ranged from 1.0 to 1.2%. Westcott Hood... 

Vitrinite reflectance data (Rq) for the thermally altered samples (Fig. 11) follow the same trend above and below the sill. The Rq values increase with increasing alteration temperature and plateau above 400°C. The Rq values range from 0.23 to 3.24%, whereas the Rq values of the in situ samples range from 0.25 to 4.81% (Simoneit et al, 1981 Peters et al, 1978, 1983). The laboratory alteration temperatures and corresponding vitrinite reflectance values of the kerogens fit with the temperatures inferred from the in situ Rq data (Peters et al, 1978). The Rq values of the unheated rocks combined for the composited samples (1 and 8) were estimated from the data for the in situ samples. 

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... 

Range of reflectance values, 1.5-6.5% sample contained roughly 5% vitrinite as impurity. 

Prior to measurement of reflectance, the sample face is covered with cedar oil or commercial immersion oil and then multiple readings are taken of the maximum reflectance of the coal component (e.g., vitrinite) of interest. These values are compared with readings of high-index glass standards (of known reflectance) that are available with reflectance values typically ranging from 0.302 to 1.815%. 

Figure 3 Vitrinite reflectance is used to provide an indication of the maturity of a source rock or potential source rock. The approximate values for the onset of oil generation, peak oil generation, and onset of gas generation are also shown in this diagram. It should he noted that there is some disagreement as to the precise values for these ditferent processes (Hunt, 1996) (reproduced hy permission of Freeman from Petroleum Geochemistry and...

Figure 4). Unfortunately, even when a reflectance value is available, it may not be reported in scientiflc publications. I strongly recommend that petrographic analyses and vitrinite reflectance be reported for samples on which structural studies are conducted.

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