Keywords: 
• immature oil /
• low mature oil /
• chemical kinetics /
• mechanism of hydrocarbon generation

Abstract: Representative samples from various geological conditions, such as special type of organic matter(suherenite, resinite and some kind of algae),organic matters ( OM ) reworked intensively by bacteria both in natural geological situation and lahoratorv, OM rich in sulfur existed in strong reductive environment and soluble OM, all these have been reported to have close relationship to the occurrence and enrichment of immature to low-mature oil.In addition some reference samples are collected in this paper. Based on the combination of constant heating experiments and the PY-GC techniques the relationship between the heating temperature and transformation ratio of OM to hydrocarbon(oil+gas),to oil and to gas for each sample mentioned above are obtained respectively. Afterwards the chemical kinetics behavior of OM to hvdrocarhon, to oil and to gas for each sample are discussed svstematicallv with the model of parallel first order reactions.The results indicate that: 1)the activation energy of OM to oil is generally lower than that of gas and the activation energy of OM to hydrocarbon is located in between of the above two or is close to one of them. These reflect the essential of the OM to gas is more difficult than it to gas and the process of hvdrocarbon generation is the superimposition of the process of OM to oil and to gas, 2) The weighted average activation energies of hydrocarbon generation from resinite, suherenite, OM rich in sulfur oil shale rich in algae biodegraded amorphous A formed from type I OM reworked intensively by microbe as well as soluble OM are indeed lower(the average activation energics of OM to oil and to hvdrocarhon are less than 197 kJ/mol and the one of OM to gas is less than 210 kJ/mol) than that of common kcrogcn.This is coincident with the fact that all these OM are closclv related to the occurrence of immature to low mature oil, which were reported cxtcnsivclv in literature.At the same time it can he seen that the activation energy of biodegraded amorphous D is lower than that of the same type of OM and the activation energy of OM reworked by microbe in lahoratorv shows somewhat decrease.This means that the intensive reworking of OM by microbe is favorable for the carlv generation of petroleum.The results mentioned above suggested that although the occurrence and enrichment of immature to low mature oil may relate to number of different geological conditions or factors their commonness is that thcv all have lower activation energy of hvdrocarhon generation than that of normal OM. The initial application of the chemical kinetics models shows that the OMs mentioned above do generate a larger amount of hvdrocarhons in a burial depth shallower than that of hvdrocarhon generation threshold for normal OM.This elucidates quantitativclv the generating mechanism of immature to low mature oil existed in various geological conditions.The study of this paper believes that not onlv it is theoretical credihility but also practical fcasihilitv to study the generation mechanism of immature to low mature from the theory of chemical kinetics.