The radioactivity well logging was applied to the Oil Mining Industry in Japan. This imported instrument was tested in Akita oil field. Reliable records were obtaind by four well loggings. Then, this method can be employed to obtain an information in secondary recovery operations.
The Mogami oil field has been known for a long time but it has not been exploited. After the war, the Mogami oil field was again surveied theoretically and test holes were drilled on the Tominami anticline in the Horinouch area which has been newly discovered. The results obtained from the geological survey and the drilling of test holes; namely geological succession, paleontological data, gravity investigation of cores, speed of drilling and bottom hole pressur, etc are descrived in this paper.