The writer reported that the sandstones in this area were composed of material supplied from the topographical high place by mass flowes such as turbidity currents, and that thick sandstone developed in WNW-ESE and -SE directions decreasing thickness and turbulence from the central to the marginal (remote) area (Part 1, Jour. Jap. Assoc. Petrol. Techn., Vol. 30, No. 2, 1965). Porosity of the sandstone decreases with increasing median diameter and standard deviation of grains, and with increasing bed thickness. Therefore sandstones in the marginal area are more porous than in the central area, but thier capacity as oil reservoir is large in both the central and the middle areas, and small in the marginal area. Permeability of the sandstone decreases with decreasing porosity and increasing standard deviation of grain size, but has no relation to the median diameter. Permeability of the sandstone decreases when bed thickness increases, and the sandstones in the marginal area are more permeable than those in the central area. Thus the sandstones in the middle area as well as in the central area are suitable for reservoirs, while those in the marginal area are more porous and permeable in spite of their thinness. The sandstone fabrics control the directional permeability. Permeability of the sandstone is maximum in the direction parallel to the current flow which carried sand grains at the time of deppsition and minimum in the direction perpendicular to bedding plane. It is concluded that these characters should be taken into consideration in petroleum exploration and exploitation works.
By the use of drilling records taken in oil fields in Japan, the factors affecting penetration rate of a rotary drilling were analysed. Some of the results obtained are as follows: (1) In some fields there is a relationship between load on a bit and penetration rate both for vertical wells and directional wells drilled with a vertical deviation angle of less than 40 degree. (2) In other fields there is no special relationship between bit load and penetration rate. In these fields hydraulic factors must be considered to analyse the penetration rate. (3) When soft mudstone (its compressive strength: 135kg/cm2) at a depth of 3700 meter was drilled with heavy bit load, it gave a very low penetration rate because the pressure caused by a long column of mud fluid was very high.
Two short papers concerning the measurement of compaction in shale have recently appeared in the Journal of Sedimentary Petrology: Shelton, 1962, dealing with shale laminae in the Cretaceous Dakota Sandstone, and Ferguson, 1963, concerning a Scottish Lower Carboniferous shale. There are some ways for determining compaction factor: "Porosity-depth (shale) " method (Hosoi, 1963), powdering and deposition method, and differential compaction method. The characteristics of each method should be considered.