Abstract: Maturity Assessment from Suppressed Vitrinite Reflectance

H. B. Lo, E. I. Sandvik

Vitrinite reflectance (VR) continues to be an important tool for assessing the level of thermal maturity. This talk describes an improved method for correcting the suppression of VR that occurs in hydrogen-rich sediments. In hydrogen-rich sediments the analyst frequently reports VR values significantly lower than would be expected for non-suppressed, "true" vitrinite samples. If uncorrected, this can cause substantial underestimation of maturity levels and, consequently, incorrect estimates of hydrocarbon generation and maturation timing. The improved correction procedure for correction of suppressed VR is based on measurements with a number of laboratory-matured coal and sediment samples. The procedure has been tested with several naturally matured sample sets from North America, Eur pe, and Australia, and has been found to give reasonable results. It is applicable to samples having initial hydrogen indices (HI) of 150 mg/g or more.

In dealing with possibly suppressed vitrinite reflectance, it is important to recognize that the suppressed reflectance values are a consequence of two factors. The first is the presence of hydrogen-rich vitrinite-like macerals and the second is the identification of these macerals by the analyst as "true" vitrinite. Therefore, the fact that different analysts will have different results on the same samples must be recognized. The approach for dealing with this is to select a group of closely spaced samples (all should have the same maturity) and identify lower and upper bounds that bracket the "true" VR. Procedures used to estimate the lower bound and the upper bound of the "true" VR will be explained in detail.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994