The theory of inorganic origin of petroleum was proposed mainly by chemists who could synthesize hydrocarbons in laboratorys. However, since biological markers which can be formed only by living organisms were discovered incrude oils, the theory of organic origin had recieved much support from many workers.
The direct origin from living organisms and proto petroleum origin in the theory of organic origin declined already because it was difficult to explane the primarymigration of the above origins. As a result, the theory of kerogen origin was raised rapidly. The kerogen is insoluble organic matter by soluvents, and contains over about 90 percent in sedimentary organic matter. Moreover, the kerogen generates hydrocarbons by the thermal distillation.
Petroleum source rocks and reservoir rocks are entitled for muddy rocks having abundant organic matter, and for sand stones or carbonates having high porosity and permeability, respectively.
Commercial oils were genetates by the thermal transformation of the ketogen in source rockes, migrated, and accumulated in reservoir rocks. A mechanism of the primary migration of oils from kerogen is explaned by the oil phase or gas phase transport.
Recently, immature oils were found in many fields. In this paper, possibility of the origin of immature oils is discussed, but the detailed study of this problem is required in the future.
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