No significant oil or gas fields were found in the Ishikari-Hidaka Area despite the exploration activities carried out for a long period. Since 1970, several deep wells have been drilled in the area and subsurface geological data were derived for regional control. Hydrocarbon exploration to date has discovered sandstones of the Ishikari Group with potential reservoir characteristics. No other important sandstone nor any carbonate reservoir targets were revealed in the area. Volcanic reservoirs are expected to be one of the important targets in future exploration here as has been found in the Northeast Inner Japan Area where approximately fifty percent of oil and gas production has derived from volcanic or pyroclastic reservoirs. The western half of the Ishikari-Hidaka Area is adjacent to the "Green Tuff" Area of Southwestern Hokkaido. Therefore, it is thought that the area has been considerably affected by volcanic activity. In this paper, the area is subdivided into four tectonic provinces and the stages and rock facies of the volcanic and pyroclastic rocks of these provinces are reviewed.
This study is a basic resarch which has been conducted to investigate the effect of oil recovery by nonionic surfactant flooding under the low concentration of the same. For the purpose, two kinds of surfactant were selected as samples. One of them was polyethylene glycol-polypropylene glycol ether and the other was polyethylene glycol-nonylphenol ether. In the first type, polyethylene glycol-polypropylene glycol ether, we prepare chemicals, which have various mole numbers of ethylene oxide and molecular weight of polypropylene. Concerning their low concentration, the interfacial tension between crude oil and oil recovery efficiency were measured at every temperature. From these results, we recongnized extremely low interfacial tensions and higher recovery of residual oil when molecular weight of polypropylene glycols were 3, 000 to 4, 000 and ethylene oxide contents were 30 to 40 percent at 30°C to 40°C of test temperature. In the second type, nonylphenol ether, the lowest interfacial tensions were obtained at 9 to 10 polymerized degrees of ethylene oxide in these surfactants, but the most recoverable efficiency was shown at 7 to 9 polymerized degrees. We could not get the clear relationship between interfacial tension and recovery efficiency in this type of surfactant.