In this paper the writers describe a new natural accumulation of small scale in the western part of Shizuoka Prefecture. Methane gas occurs in the alluvial deposits which fill the drowned valley of the River Kiku and cover Neogene formations. Through geological and geochemical studies, they come to a conclusion that although the gas was, for the most part, generated in the muddy alluvial deposits and probably the generation is still in progress, it is probable that a part of the gas was derived from the underlying Neogene formations.
Simplified penetration-test shows the relative value of consolidation for sedimentary rocks as well as soil. This method is to measure the press-mark which is made by falling some metal instrument (cone, awl or steel ball) on the horizontal surface of rocks, and is available for the geological field-works and core-tests.
The writers used sodium silicate-C. M. C.-Surfactant mud (S, G 2.20) for drilling the high pressure heaving shale zone of Hachikoku S. K. I, in 1957. In this paper, they describe about the effects of the mud tested in both laboratory and field.
Experiments on the invasion of mud fluid into free gas zone are described in this paper. As porus media both unconsolidated sands and artificial consolidated sands are used. The data and results are presented in two parts: (1) a study on the length of invasion of mud and filtrate into sands, and (2) a study of the degree and extent of reduction of the gas permeability of sands by mud invasion.