Transformation of clay mineral facies in mudstones have been controlled mainly by overburden pressure and geothermal temperature. In primary migration of proto-petroleum from source rocks to reservoirs, expulsion of absorbed water in the swelling clay minerals by overburden pressure is considered to be very important. For the solution of these problems, study of compaction on various clays under high pressure and certain temperature is necessary. The writers, therefore, manufactured the triaxial, hydrostatic compaction apparatus which can increase the pressure to 1500kg/cm2 and the temperature to 150°C in maximum. Compaction on Na-montmorillontie and kaolinite clays have been conducted under the condition at 500kg/cm2 and room temperature. Water content in montmorillonite clay decreased gradually in straight, while those of kaolinite clay decreased rapidly by compaction. After 6 day's continuous experiments, there were no apprent changes in the mineralogical form of these clays.
Distribution of normal alkane hydrocarbons in sediments and crude oils of the oilfields in Japan were studied. Carbon preference indices of heavy normal alkanes (CPI) range from 1.41 to 3.00 for recent sediments, 1.01 to 6.41 for ancient sediments and 0.94 to 1.30 for crude oils. CPI is generally reduced with depth and inversely related to hydrocarbon/organic carbon ratio and heavier gaseous hydrocarbon/methane ratio in the mudstones from drilled wells. The relation between CPI and hydrocarbon/organic carbon ratio is not reciprocally proportional but rather hyperbotal. During early compaction stage which releases quantities of water the ratio is apparently invariable in accordance with the reduction of CPI, while it increases proportionally with CPI reduction during middle compaction stage of mild dewatering. At the transition point between early and middle compaction stages in MITI Hamayuchi, Hokkaido, distributions of normal alkane change to n-docosane or n-tricosane from n-heptacosane or n-nonacosane in their maximum frequencies. The depth and temperature of this transition point are about two kilometers and sixty centigrades respectively. This transitional point may suggests the initial stage of maturation of petroleum by thermal transformation from insoluble organic matters.
It is well known that seismic reflection events are originated by a sequence of subsurface reflecting interfaces which is represented by a series of reflection coefficients. For the investigation of the reflection phenomenon, the so-called synthetic seismogram which is calculated from the reflection coefficients series, is used. Each reflection coefficent is connected to both velocity and density logging data. However the density data are not always available, then the synthetic seismograms have been quite often caluclated only by velocity data, approximately neglecting the density variations in comparison with the velocity changes without sufficient examinations. Accordingly the reflection coefficient computed with velocity data and with or without density data is investigated in detail. Furthermore the. resulting synthetic seismogram is also studied from this point of view. In addition to the aboves, the distributions of velocity vs. density are investigated with actual well logging data. Certain dependence of the variance of reflection coefficients upon the multiple events is studied using an artificial reflection coefficient series simulated by a sequence of random numbers.