Kozo Kawai

Relationship between crude-oil properties and geology in some oil and gas fields in the Niigata basin, Japan

Abstract The crude oil separately sampled from every producing well in the two fields in the Niigata Neogene sedimentary basin was analysed chemically and tested physically. The data obtained were interpreted, taking the geological conditions of the reservoir fully into consideration. In the Minami-Aga field, the reservoir conditions are rather simple, but detailed examinations of the conditions reveal that the reservoir can be divided into three blocks. The Minami-Aga crude has, as a whole, smaller variations of properties, but the differences in the reservoir conditions have influenced the crude-oil properties to a considerable degree. The crude oil from the Ie reservoir in the Kubiki (Katamachi) field is, as a whole, less evolved than and quite different from that from the Minami-Aga field. The conditions of the Ie reservoir are greatly variable within a short distance. The crude-oil properties vary extremely, generally corresponding to the variations of the reservoir conditions. No abundance ratios of hydrocarbon isomers are found to characterize the Kubiki crude, or to have remained almost constant during the time of secondary migration and accumulation of the oil. Alteration of crude oil by interstitial water seems to have influenced the oil properties, especially in the Kubiki field. From the chemical composition of the crude oil, the directions of secondary migration of oil were inferred. In addition, special consideration is given to the evolution of oil.

Tertiary Formations in the Ota-Omama District, Gunma Prefecture, with Special Reference to the Paleogeography of the Northwestern Kantõ Region in the Late Miocene Age

The stratigraphy and the structure of the formations of middle Miocene to Pliocene in age in the Ota-Omama district, are described. In connection with the paleogeography of the northwestern Kanto region, the writers stress that the upper Miocene marine sediments influenced strongly by the oceanic waters at the time of their deposition are distributed in the district.

Natural Gas in the Ogasa-machi District, Shizuoka Prefecture

In this paper the writers describe a new natural accumulation of small scale in the western part of Shizuoka Prefecture. Methane gas occurs in the alluvial deposits which fill the drowned valley of the River Kiku and cover Neogene formations. Through geological and geochemical studies, they come to a conclusion that although the gas was, for the most part, generated in the muddy alluvial deposits and probably the generation is still in progress, it is probable that a part of the gas was derived from the underlying Neogene formations.