化学反応速度論的立場からみた石油の発生深度

(1) 石油生成の化学反応速度論とロパテンーウエイプル法

抄録

The objective of this paper is to describe the importance concerning the conversion of high sulphur kerogens (type II-S) to petroleum. Those kerogens are known to be derived from siliceous and carbonate source rocks and to bigin the conversion even earlier, possibly due to the abundance of sulphur bonds compared with other types of kerogen (Orr, 1986). In general, however, it is difficult to make a direct comparison of the timing of oil generation among different kerogen types on the basis of geological data such as hydrocarbon ratio and/or vitrinite reflectance. Moreover, there has been a controversy about determining oil generation thresholds using the vitrinite reflectance (Ro) for different kerogen types.
Consequently, in this paper, the timing of petroleum generation for different types of kerogen is examined from the standpoint of kinetic models as reported by Tissot and Ungerer (1990). However, until recently, most exploration geologists were not familiar enough with organic geochemistry to use kinetic models, and preferred the simplified model of Lopatin-Waples method (Waples, 1980) which assumed reaction rates to double for each 10°C increase.
From the viewpoint of the above, in the first report, the chemical kinetic modelling of petroleum generation reported by many researchers is outlined briefly and then it is pointed out that TTI model (Lopatin-Waples method) has no theoretical basis and is not suitable for modelling oil generation based on the comparison of TTI with kinetic model of oil generation.
In the second report, it is emphasized that high sulphur kerogen begins to generate hydrocarbons remarkably earlier than other kerogens do according to the kinetic model (Tissot and Ungerer, 1990) and that this phenomenon is important for the origin of immature or shallow depth oils and the exploration of those oils. Finally, it is suggested that oil from the high sulphur kerogen might be generated during diagenetic stage, if we consider the origin of high sulphur kerogen and try to apply the kinetic calculation to the organic matter in diagenetic stage.