Study On Molecular Structure Characteristics Of Fractions And Catalytic Aaquathermolysis Of Shengli Heavy Oil

Due to the growing world-wide energy demand and scarcity of the conventional oil reserves,increasing attention is turning towards rich unconventional resources such as heavy oil.Heavy oil reserves are abundant in the world,which contain about two thirds of the total remaining reserves.However,extremely high viscosity and poor fluidity are examples of the challenges in their exploitation,transportation and processing.Therefore,many techniques such as steam soaking,steam drive,and in situ combustion,have been developed and adopted for heavy oil exploitation.The method has been proved to be effective for ordinary heavy oil,but not for extra heavy oil.Aquathermolysis was thus developed to resolve the challenge,which was also enlightened from the thermolysis during the petroleum refining.The key of the technology is to synthetize appropriate catalysts and investigate the mechanism of viscosity reduction.In the thesis,physico-chemical properties of 6 kinds of Shengli heavy oils were studied to investigate the high viscosity mechanism of these heavy oil.Thereafter,several initiators were introduced to reduce the reaction temperature and an optimal one was selected in the followed experiments.An amphiphilic catalyst was synthetized and used to perform aquathermolysis experiments.The mechanism of catalytic aquathermolysis reducing the viscosity of the heavy oil was discussed.On this basis,filed tests were carried out and satisfactory results were obtained.The major findings are listed as follows:Micro-properties of 6 kinds of heavy oils sampled from Shengli Oilfield were studied to investigate the high viscosity mechanism of the heavy oil.Thereafter,average molecular weight,polarity,elemental composition,and average molecular structure of the heavy oil were characterized.Moreover,the correlation between the viscosity-temperature characteristics and colloidal stability were studied.Results indicated that various fractions in these heavy oil were different,of which the viscosity increased as a result of increase in resins and asphaltenes content.More importantly,the heavy oil viscosity were closely related to the sum of resins and asphaltenes content,average molecular weight and polarity of the two above mentioned compounds.From saturates,aromatics,resins to asphaltene,H content decreased,C content and heteroatomic compounds content increased,and increase occurredfor the number of aromatic compounds and average molecular structure.It was found that molecular structures of asphaltene in various heavy oil were varied,which possibly be the main cause for the different viscosity of these heavy oil.Besides,no correlation was found between the colloidal stability of the heavy oils and their viscosity.Aquathermolysis experiments were performed to evaluate various influence factors on viscosity reduction of the heavy oil.Initiators were also introduced in the aquathermolysis process to strengthen the adaptability of the catalyst system in the reservoir condition.The synergism of initiator and catalyst was studied.It was found that catalyst and initiator had a synergistic effect on decreasing the reaction temperature,in which the viscosity reduction at150 °C was compared with that of at 250°C with no initiator used.With increasing the initiator content,the viscosity reduction was again decreased.An interfacial active cobalt complex was synthesized and used in the aquathermolysis process.In order to investigate the mechanism of the aquathermolysis,the electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry(ESI FT-ICR MS)and X-ray absorption near edge structure(XANES)were used to characterize the molecular structure of the heteroatomic compounds in various resins and asphaltene.The results showed that the aromatic-carbon ratio,aromatic ring number of the catalyzed components decreased with increasing of H/C ratio,condensation degree of the aromatic compounds,and branching index of the carbon chain.These results indicated that series of hydrogenation,ring-opening,chain rupture,desulfurization,and denitrification occurred during the catalytic processing.After that,super-molecule were transferred into light hydrocarbons,which was contributed to decreasing the viscosity of the heavy oil.Moreover,the main existing forms of the sulfide in the asphaltene were thiophene,sulfoxide,while content of sulphone and sulfate were relatively less.Thiophenes were usually found to be aggregated in the aromatic ring with alkyl side chain.They were distributed around the asphaltene,but not in the core.Physical stimulation experiments were carried out to evaluate the catalyst and obtain optimum conditions.Thereafter,suitable oil wells were selected for the field test.Numerical simulation was then carried out to obtain optimum injection time,injection mode,the number of slug and slug size.On this basis,catalytic aquathermolysis process had been carried out on6 oil wells,where the cycle oil/gas ratio was greatly improved and period input-output ratio reached to 1:3.2.