Two examples of oil seeps were found in 1954 in serpentine rocks of Hokkaido. These are the first occurrences discovered in such kind of rocks, although many showings had been previously found in areas of eruptive rocks in Japan. One of these seeps is located in a tributary of the Utonai river, Nakagawa village, Teshio province of northern central Hokkaido and the other is in the Mukawa river, Hobetsu village, Iburi province of the southern central Hokkaido. This paper describes its unusual type of oil seep and the related geology of the Utonai and the rare type of oil at the seep is also discussed. The crude oil is from fissure in serpentine. It is colorless, transparent and clear in appearance with a gasoline like smell and is probably natural gasoline. It is very light in specific gravity measuring 0.7707 at a temperature of 15.4°C. Its viscosity is also low which is 1.190 centipoise at a temperature of 30.0°C. and very gradually increases with increases in temperature. The behavior of the crude oil upon distillation is unusual. That is, it has a initial boiling point at 62.0°C. and is 98% of oil distilled out at a temperature of 246.0°C. The author concludes that the oil in the serpentine mass migrated from the surrounding Cretaceous oilbearing marine deposits after the serpentine intrusion into the Cretaceous. The characteristic properties of the crude oil developed by natural cracking resulting from residual heat in the igneous body. Decolorization caused by passing through clay within the serpentine as the oil moved up to the surface. The economical impotance of this field is still unknown but this occurrence suggests that more attention should be paid to the oil possibilities of the Cretaceous formations of the surounding region.
In the former report, the auther testred the effectiveness of various amine-type inhibitors and found that galvanic currents between brass and steel were corresponding to the effectiveness of inhibitors in corrosive media inhibited by those compounds. So the auther have measured the current in the gas-well inhibited by cetyl amine-type compounds. Results of them showed that the gas well was kept in favorable conditions.
The calcareous materials of gas formations in Mobara gas field are soluble to hydrochloric acid, and the original permeability of formations can thus be greatly changed. This causes the increase of gas and water production. In this report the following is explained: 1. The method of accidizing. 2. The combination of acidizing and fracturing. 3. The combination of accidizing and gravel packing. 4. The result of acidizing in Mobara gas field.