From the point of view of the stratigraphy of the oil or gas fields in Japan, it is very important to establish the methods of identifying or distinguishing vitric tuff beds which are intercalated in the Neogene formations and serve as horizon-markers. For the above purpose, we carried out spectrochemical analysis of many tuff samples from the Maego district, Akita Prefecture, and also measured refractive indices of volcanis glasses in them. Through this preliminary study we have come to the following conclusions: (1) Such elements as V, Zr, Pb, Co, Ni, and B, and refractive indices of volcanic glasses clearly characterize some tuff beds of similar lithology. (2) Because of the irregularity of the distribution of the elements in any tuff bed, which is partly due to impurities and alteration, sampling tuffs and treating the samples must be carefully conducted.
The permeabiligy of fracturing sand has an effect on fracturing result straightly, as the productivity increase by fracturing is due to the highly permeable sand bed, which is newly formed by packing fractures with sand, and more oil moves along easier into the well bore. In this paper the discussion is made on factors controlling the permeability of fracturing sand, and on the method of obtaining the fracturing sand permeabiligy. The comparatively good coincidense is obtained between experimental values and calculated values of fracturing sand. However, suitable value of sphericity factor must be counted.
Results of a study on the invasion of mud fluid into gas-dissolved water zone tested by the use of artificial consolidated sands are described in this paper. Some of the results obtained are as follows: (1) when water pressure is low, a mud cake interrupts flow of water, (2) more mud fluid invades into a sand of higher permeability, (3) therefore, the degree of reduction of water permeability is conspicuous in a sand of higher permeability, and (4) when water pressure is high, invasion of mud fluid affects little upon the water permeability.