In July and August of 1949, the writer carried out a precise geological survey over a part of margin land of Niigata oil field, east of omo oil field, jointly with K. Ida, Y. Ishiwada and T. Mitsunashi. The general stratigraphic succession is as follows: In the area under discussion, the Imogawa black mudstone formation is interfingered by the Niwazuki pyroclastic member. The latter consists mainly of dacite-pumiceous tuff, partially including subangular pebble or boulder of the dacite and black mudstone. The boundaries between them are remarkably clear and uneven, and a lot of blocks of black mudstone and hard black shale are scattered in the tuff near on the boundaries to the mudstone. As shown in the figure, the distribution of the pyroclastic member is quite different between on the both wings of the anticline or syncline. This geologic structure has no connection with the "Niigata trend", and might be produced by volcanic activities simultaneous with deposition, resulting in the unusual distribution and shape of the tuff.
Because flow of fluids in an oil reservoir tapped by a well is not subject to the Darcy's law, it produces one of the most complex problems in oil reservoir engineering. In this paper, a method of calculation to obtain pressure gradient in an oil reservoir is described. The results calculated are shown in the figures, and they indicate how radically different the flow of gas-dissolved oil is from that of homogeneous fluid.
After the war the developments of petroleum exploration geophysics in the United states have been rapidly made owing to the astounding developments in electronics and aviation. Both instruments and field techniques in seismic, gravity, and magnetic exploration have been exceptionally revolutionized. It has been possible to realize three dimentional survey from the air, the ground, and the subsurface. The modern instruments, field survey, interpretation, research, and results in recent geophysical exploration are generally described.