Abstract
Microbiological studies on the Yabase and Nishiyama oil-fields in Japan were carried out. The microflora of these oil-fields were more complicated than those of the Higashiyama oil-mining gallery where petroleum is recovered by mining. Considerable numbers of bacteria were found in the oil-brines of the oil-wells from about 700m in depth, but recognizable numbers of microorganisms were not found from depths of over 1, 000m. Pseudomonads were widely distributed in the samples obtained at these oil-fields, and hydrocarbon-utilizing bacteria, including methane-oxidizers, were found in the injection water of the waterflood, bottom water of oil-tanks, etc. Taxonomic studies of the isolated bacteria revealed that the species differed with the oil-producing district, even though the crude oil was produced from the same oil-zone. The microflora of the oil-brines were greatly different from those of the surface ground. From these facts, the use of bacterial tracers in petroleum mining was suggested.
