It has been generally accepted that kerogen is the source material of petroleum. The author has performed isothermal pyrolyses of kerogen isolated from mudstone of the Onnagawa Formation ((Middle Miocene) at Anzen-zi in Oga Peninsula, Akita Pref., Japan. Thermal decomposition of kerogen is accompanied with the generation of bitumen. The products were separated into hydrocarbons, O-N-S compounds and residue by the technique of liquid chromatography over activated alumina. Hydrocarbons and O-N-S compounds are said to be formed competitively or successively. So, the author made two mathematical reaction models based upon these assumptions. Kinetic parameters of the generation of O-N-S comp. (+hydrocarbons) were calculated by the technique of multivariate analysis or multiple regression analysis. (To be continued)
The accuracy of the log analysis with the use of Computer Processed Interpretation (CPI) in shaly sand, depends mainly on the proper selection of the type of equation (interrelation of Sw, φ, Rt, Vcl…) and the values of the parameters to be used therein. Therefore, prior to starting the analysis, it is most desirable to establish the equation which is adequate for the local geological conditions. However, voluminous data and many hours will be required for such purpose. In the case of the Agaoki oil and gas field, from the study of well log data and test results of wild cat wells, it was concluded that actually, satisfactory results could be obtained by the use of properly controlled Cementation Factor m, and Saturation exponent n. In actual well log analysis of development wells, satisfactory results have been obtained by using values of m=2.3 and n=1.4. Originally these parametric values were, empirically decided to compensate the difference between the results derived from log interpretation and results from core and production tests. These values have been also supported by a method of studying logical papmeters through log data, which is a method newly developed in this field, using log derived values only. (To be continued)
The sedimentary facies which has strong relation to productivity was studied. The relations between porosity and permeability in different sedimentary facies were plotted and these data show that limemud contents in the sediment control the permeability. Chalky limemud deposited under low energy wave condition has good porosity but it has very low permeability. These sediments were studied under the microscope and scanning electron microscope (SEM). These studies reveal that the pores in such chalk and chalky limemud are made up mainly of very fine intercrystalline pores which are able to observed under the SEM. The differences between core porosity measured by helium gas and visual porosity observed under the microscope are compared with permeability obtained by core analysis. The result shows that the latter shows better relation than the former to permeability. Such relation was examined using recent limemud changing the mud content in oolitic sand. The result coincides very well with the relation obtained in core samples. The diagenesis of the carbonate was studied especially on the cementation which controled the porosity change. The porosity change in the grainstone is much influenced by the cementation of sparite, but in chalk or chalky limemudstone the porosity does not decrease so much, because there is no pore space large enough for sparite precipitation. The porosity changes versus depths show the two types of characters. The porous zone in the Thamama Zone II (Lower Cretaceous) has linear relation between poresity and depth. However, those in the deeper oil zones (Thamama IVA and Yamama VA, B) show the linear relation between present pcrosity and relative depth at the end of the Dammam age (Eocene). These phenomena show that the porosity of Zone II decreases down-flank with increase of depth. But the porosity in deeper zones decreased before Miocene movement.
Porosity, permeability, and seismic wave velocity of 48 carbonate rocks among which 41 were taken from Japan and 7 were from other countries were measured. Density of the Japanese limestones ranges between 2.658 and 2.741g/cm3. The crystalline limestones show rather constant density and the relation between its value and porosity is not clear. Porosity of the Paleozoic non-crystalline limestones ranges between 0.01 and 0.04%, wheras that of Mesozoic limestones between 0.02 and 0.1%. The ratio of P-wave to S-wave is almost constant. Further discussion on relations among porosity, grain size, seismic wave velocity and permeability was done.
Diagenesis is defined as the process involving physical and chemical changes in sediment after deposition that converts it to consolidated rock. Carbonate rocks are mainly composed of carbonate minerals only and have a polygenic origin, and thus are different considerably from clastic and pyroclastic rocks. Quantitative and qualitative changes of grains (mineral composition and chemistry) and pores (petrop-hysical properties such as porosity and permeability) in carbonate rocks during each stage of dagenesis (compaction, fracturing, solution, cementation and transformation) were discussed in detail. The conclusion is that diagenetic changes in carbonate rocks is chiefly controlled by the chemistry of fluids (pH, Eh and ions) in pores rather than the physical factors such as overburden pressure, geothermal temperature and geologic time.
Bioreef is a site of the highest diversity of biota on the earth's surface. Geohistorically, however, it was a sort of fairly simple mound in the Precambrian Era as exemplified by a stromatolitic hump. The early Cambrian archaeocyathid reef was monotonous but the first true bioreef made by calcium carbonate-secreting marine animals. The Paleozoic and later coral reefs have been much amplified in their constitutions through ages. It was stressed that the ecological reefs should clearly be distinguished from the stratigraphic ones by paleoecological analysis. The bioreef is here subdivided into four main ecological types, i.e, the isolated island type, the plateau island type, the continental shelf type and the shelf margin type. They are characterized by respective grades of development of the skirts that frill the reefs. Bioreefs formed on a shallow and wide shelf like the Great Barrier Reef are associated with well-developed inter-reef or back-reef type stagnant basins which bear a high potentiality of metamorphism of the organic materials derived from the reef biota into petroleum. Excretion and bioerosion of reef inhabitants are described as the important agencies of a biochemical activity for destructive and diagenetic processes of the reefs. Finally, a hypothetical classification of several limestone bodies in Japan is proposed on the basis of paleoecological megastructures of these carbonate sediments.
This paper describes same features of strontium which was often used as the indicator for the paleoenvironmental analysis, and presents examples on the paleoenvironmental analysis based upon the geochemical results. The interpretation of geochemical results must be done with help of sedimentological, mineralogical, petrological and paleontological data.