Kazuo Taguchi

Basic nitrogen compounds in bitumen and crude oils

Abstract Basic nitrogen compounds in bitumen and crude oils were analyzed by acid extraction, column liquid chromatography and gas chromatography—mass spectrometry. Various kinds of azaarenes and azadibenzothiophenes are found in both bitumens and crude oils, except cyclic amides which are found only in bitumens. It is suggested that basic nitrogen heterocycles found in the bitumens from non-marine sediments are generated mostly from the high M.W. geo-polymers during the later stage of diagenesis, based on the variation of their amounts with increasing maturity. The difference in the ratio of 2-ring to 3-ring azaarenes found between marine and non-marine sediments seems to reflect the influence of the depositional environments. A large difference in the distribution of C 1 /1bC 4 alkyl homologues and isomers of azaphenanthrenes between bitumens and crude oils is observed. The isomers with nitrogen atoms masked by the side chains are found in both bitumens and crude oils, while the isomers with exposed nitrogen atoms are seen only in bitumens. These differences are attributed to the preferential migration of higher homologues and nitrogen-masked isomers caused by their weak adsorption on clay minerals during primary migration of oils.

Timing of oil generation considered from chemical kinetics-A review. (1) Outline of kinetics of oil formation, and comparison of TTI (Lopatin-Waples method) and kinetic calculations of oil generation model.

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.

Vitrinite reflectance and ESR properties of organic particles, and clay minerals in DSDP Leg 50 sediments

Abstract As part of the geochemical studies of DSDP Leg 50, 52 samples of sediments from the Moroccan Basin of the Atlantic Ocean were analyzed to obtain information with depth variation of the organic richness, maturity and composition, and of mineral constituents in the sediments. The organic carbon content shows a remarkable variation which can be attributed to the turbidite sequences and its vertical distribution shows an overall decreasing concentration with depth in relation to the turbidite sedimentation. Most of the sediments from Hole 416A may be regarded as possible or marginal potential source rocks, based on both organic carbon and calcium carbonate contents. The results of vitrinite reflectance measurements indicate that all of the samples analyzed are immature thermally and they have not reached the level at which petroleum generation begins. However, the g values from the Cretaceous sediments show a progressive decrease with increasing depth. Combination of the results suggests that the organic matter was derived mostly from terrigenous plants, but a significant proportion of the sediments still have the possibility that they have the favorable kerogen type for petroleum generation. No particular correlation has been observed between mineral composition, and organic matter types and contents.