Vitrinite reflectance: introduction and sources of error

Brian J. Cardott, Oklahoma Geological Survey, Norman, OK

Coal rank or thermal maturity refers to the level of coalification or maturation of organic matter indicated by changes in physical, chemical, and petrographic properties from increasing temperature and time.  Thermal maturity is one of three important factors in evaluating hydrocarbon source rocks and unconventional energy resources such as gas shales and oil shales.  The other two factors are kerogen (organic matter) type and quantity.  Vitrinite is a coal maceral derived from the lignin and cellulose of plant cell walls and fillings.  Vitrinite reflectance (%Ro) is a measurement of the percentage of light reflected off the vitrinite maceral at high (500X) magnification in oil immersion.  Vitrinite reflectance has become the standard thermal maturity indicator.  It is not as dependent on kerogen types, bitumen content, or contamination as organic geochemical techniques.  However, there are disadvantages and limitations to the technique.

The goals of the presentation are to answer the following questions: What is vitrinite? What age rocks does it occur in? How much sample is needed? What is vitrinite reflectance? How is it measured? How does it change with increasing rank or thermal maturity? What are the sources of error (e.g., samples and equipment)? What is vitrinite-like organic matter? What is reflectance suppression? How can I distinguish good data from bad data?