Fluid pressure gradients in shales can be determined by the porosity distributios of the incompletly compacted shales. It is possibel, therefore, to estimate permeability changes in shales by using the fluid pressure gradient (derived from the shale porosity distribution) and Darcy's law. The integration of these permeability changes with porosity values in shales can be used to establish a relation between shale porosity and permeability in the subsurface. This method of analysis applied to Cretaceous shales in Alberta and Saskatchewan, Canada, revealed that the decrase of shale permeability with decrease in porosity is less than that given by the Archie's relation, which is based on sandstone and carbonate rocks. This new knowledge ofthe porosity-permeability relation in shales promotes a better understanding og fluid movements in the shales during compaction, which will influence the migration and accumulation of hydrocarbons.
Generally the fact that residual magnetization of igneous rocks is greater than sedi-mentary rocks is well known. The authors took an interest in the measurements of residual megnetiza-tion of sedimentary rocks. Residual magnetization of rock samples of sandstone and mudstone were measured by the Astatic magnetometer. An ideal residual magnetization curve which was measured by this magnetometer was a sine curve. In the samples tested the induced magnetization appeared under the influence of terrestrial magnetic field, and this magnetization effect was marked by a shift of the sine curve. There were some samples among those tested which didn't show typical sine curves. Using the harmonic analysis the authors could separate the residual magnetization and the induced magnetization.
Characteristics of natural gas found in several Japanese fields are controlled mainly by geologic factors; particulary it was shown that the methanc contents and specific gravities of gas from the definite geologic horizons are almost similar respectively. Effects of pressure and temperature on the composition of natural gas seem to be insignificant. Chemical composition of formation water and foraminiferal distributions are closely related to the sedimentary environments of each formation. The writer supposes that the primary migration and accumulation of natural gas out of its source sediments have occured at a relatively early stage of compaction after the deposition of the sediments.