The Effect of Mineral Matrix and Seam Thickness on Reflectance of Vitrinite in High Coals
GENTZIS, THOMAS, Alberta Research Council, Devon, Alberta, Canada, FARIBORZ GOODARZI and LLOYD R. SNOWDON, Geological Survey of Canada, Calgary, Alberta, Canada, R. MARC BUSTIN, University of British Columbia, Vancouver, British Columbia, Canada, and MARCEL LABONTE, Geological Survey of Canada, Calgary, Alberta, Canada
The variation of vitrinite reflectance with respect to mineral matrix (lithology), thickness of coal seams and coal lenses, as well as type of organic matter was studied from two cores in a 550-m sedimentary succession from the Upper Jurassic-Lower Cretaceous Kootenay Group. The data obtained indicate that reflectance in high- to low-volatile bituminous coals (% Ro, max = 0.8-1.35) with depth of burial is affected by the percentage of organic matter in the samples. A positive correlation between the % Ro and the percent of organic matter and a negative correlation with the percent of mineral matter were shown to exist. It was also observed that the thicker the coal interval, the higher the reflectance. Thick coal seams (greater than 1 m) with mineral content of less than 20% generally exhibited higher vitrinite reflectance than thin coaly lenses (15-30 cm thick) with mineral content of greater than 20%. Vitrinite dispersed in sandstone--and, to a lesser extent, siltstone and carbonaceous shale--had the lowest reflectance.
Variations in vitrinite reflectance were attributed to chemical differences in the organic matter, possibly induced by degradation and diagenesis syn- or postdepositionally, the effect of geocatalysts present in the sediments, and possibly variations in thermal conductivity in the succession. Any differences in vitrinite reflectance of organic matter observed would be of great significance in the time-temperature history of a sediment needed to generate hydrocarbons.
AAPG Search and Discovery Article #91010©1991 AAPG Rocky Mountain Section Meeting, Billings, Montana, July 28-31, 1991 (2009)