SUPPRESSION OF VTRINITE REFLECTANCE IN AMORPHOUS RICH KEROGEN ‐ A MAJOR UNRECOGNIZED PROBLEM

Abstract

Vitrinite reflectance (R o ,) is regarded as one of the most, ifnot the most, powerfultools available to petroleum organic geochemistry. Yet major recognized and unrecognized problems exist concerning use of the technique. One such unrecognized problem is a major suppression of R o by significant concentrations of exinite macerals (Type I and Type II kerogen) in association with vitrinite macerals. R o values have been, and are, for the most part, read from exinite‐rich sediments examined in organic geochemical studies. This has led to the establishment of R 0 values of 0.6 (± 0.1) and 1.35 corresponding, respectively, to the regional rank necessary for the onset of significant hydrocarbon generation and for the thermal destruction of petroleum (“oil deadline”). These uniformly quoted R o values, derived from exinite‐rich (hydrogen‐rich) kerogens, would have far different values if R o had been read from vitrinite‐rich (oxygen‐rich) kerogen at the same regional rank. The serious miscalibration of the regional ranks necessary for the onset of significant petroleum generation from exinite‐rich kerogen and for the “oil deadline” have major implications for assessment of frontier areas of possible petroleum reserves as well as for petroleum exploration in general and worldwide and basin‐by‐basin resource assessment of undiscovered petroleum reserves.