Abstract
Immature kerogen samples of Type I (Eocene Green River Shale), Type II (Middle Miocene Onnagawa Shale) and Type III (Middle Miocene Sarufutsu coal) were heated at intervals of 50°C between 250 and 450°C for 30 and 150min. in a sealed glass tube under a reduced nitrogen atmosphere. After the extraction of the heated kerogens with organic solvents, IR spectra were taken with diffusion reflectance infrared spectroscopy. Maturation degrees of the heated kerogens were identified by vitrinite reflectance (Table 2).
Evolution paths of the three kerogen types were clearly shown on a diagram of aliphatic CH2(2930cm-1)/aromatic C=C(1605cm-1) vs C=O(1710cm-1)/C=C(1605cm-1) with iso-vitrinite reflectance lines (Fig. 6). This diagram is defined as an “IR maturation path diagram” to evaluate type and maturation degree of kerogens, and has advantages over Van Krevelen diagrams especially with Type I kerogen.
