Geochemical Studies On Asphaltenes And Their Possible Applications In Petroleum Exploration And Production

It is estimated that there are above 60 percent of crude oils still remained underground after exploiting by the present technologies within the world's oilfields. The total amount of residual oils is by far more than the new reserves that can be found. These residual oils exist mostly as heavy oils, extra-heavy oils and tar-mats. The heavy fractions such as asphaltenes are the main factors to make these reserves difficult to be conventionally exploited. Regarding the asphaltenes, the extensively existed and least studied fraction in oil reservoirs, this work is aimed to discuss the geochemical problems related with asphaltenes, by studying their pyrolysis kinetics, mild chemical degradation and FT-IR analysis. The results may supply technical store to the researches in petroleum exploration and recovery.The pyrolysis of asphaltenes indicates that the average activation energy is less powerful for the determination of kerogens' types. While the distribution of activation energy, since it can reflect the microscopic features of asphaltenes' cracking, could well be applied for this purpose. Regarding the asphaltenes from some specific types of kerogens, in conjunction with other results of asphaltene pyrolysis, the parameter for activation energies and their distributions can be used to mark the maturity of hydrocarbons in oil reservoirs. The kinetic parameter, frequency factor A, is of some significance in studying the potentials of secondary hydrocarbon generation. Especially at the stage the activation energy is high, the frequency factor is of great importance to guarantee the potentials of secondary hydrocarbon generation for asphaltenes. Kinetic studies on asphaltene pyrolysis indicate that the asphaltenes from type I kerogens are of great potential to regenerate oils, while the asphaltenes' potentials for oil-to-gas conversion tend to decrease in order of the primitive kerogens types of III, Hand I . The results of the pyrolysis kinetics of asphaltenes from Tarim Silurian oilsands indicate that the Silurian oilsands possess a high potential for regenerating hydrocarbons. They are mature and should be latent hydrocarbon-source rocks, hence important for the reservoir exploration related to the Silurian and especially for the gas exploration in related structures in the northern Tarim area.Regarding asphaltenes. the oxidative degradation was carried out in this work, including species of n-C- asphaltenes. crude oils and oilsands. The oxidation reagentsinclude NaI04/NaH2P04 and 30%H2O2/CH3COOH. The experimental results indicate that the efficiency of degradation decreases in the order of the species of n-C7 asphaltenes, crude oils and oilsands; and decreases in the order of the oxidation reagents by NaIO4/NaH2PO4 and 30%H202/CH3COOH. After mild chemical degradation, it is found that the asphaltenes were mostly translated into resin fractions, which can well improve the stability of crude oils according to the physical model of oil. This result has great practical significance in oil production.FT-IR analysis of asphaltenes indicates that the adsorption factor Z (I1380cm-1/i720cm-1) can well exclude the effect of maturity level, and could be used to type the primitive kerogens. Adsorption factor Y (i1600cm-1/i1450cm-1) can supply information about the evolution level of asphaltenes. and could be used to study the maturity level of oil reservoirs. According to adsorption factors A {(I2930cm.1+I2860cm-1)/(I2930cm.1+I2860cm-1/1630cm-1)}. Z (I130cm.1/I720cm-1) and in conjunction with the elemental analysis results, asphaltenes are presumed to be of some potential for hydrocarbons regeneration. The asphaltenes from type III kerogens have well prospect for gas regeneration, while asphaltenes from type I, II kerogens possess some potential to regenerate oils.Features and innovations in this work: (1) In the study on pyrolysis kinetics of asphaltenes, the geochemical significance of frequency factor A is discussed in details. The frequency factor is of great importance to guarantee the potentials of seco...