Comparison Between Immature Vitrinite and Solid Bitumen, Green River Formation, Piceance Creek Basin, Colorado: ABSTRACT

Abstract

A major problem in organic petrography is the inability to distinguish immature vitrinite from solid bitumen. For this study, several samples of coal and solid bitumen, found interlayered with oil shales of the Green River Formation, were collected from three continuous cores. Each sample was analyzed under oil immersion with reflected light, with fluorescence (blue light), and by Rock-Eval. In the uppermost part of the cores, the vitrinite and solid bitumen have identical reflectance values under oil immersion (Ro), and the structureless (nonbanded, noncellular) vitrinite is optically indistinguishable from the bitumen. Observation with blue light reveals some details in both the vitrinite and the bitumen; solid bitumen appears more granular than the vitrinite. With the yellow filter, vitrinite shows some banding and spores are visible. Without the filter, the bitumen has an orange-brown hue, whereas the vitrinite is a bright blue. Rock-Eval analysis indicated a much higher hydrogen index for the bitumen (800-850) than for the coal (400-450). The total organic carbon (TOC) was higher for the coal (50-55) than for the bitumen (20-25). In the cores examined, the vitrinite reflectance changes downhole from 0.20 to 0.55; however, the Ro for the bitumen remains constant. Because reflectance values for vitrinite and solid bitumen can be the same or very similar, a researcher should not rely on reflectance values alone to distinguish vitrinite from solid bitumen. End_of_Article - Last_Page 293------------