Research On The Downhole Pyrolysis Of Asphaltene In Heavy Oil And Application Technology

It was widely ackowledged that high viscosity makes it difficult to develop heavy oil due to more contents of heavy component such as asphaltene in heavy oil than that in regular oil. Steam flooding and steam stimulation were the major technologies to develop heavy oil at present. By using these technologies, the viscosity of the heavy oil can be reduced temporarily, while the problems in development caused by the high viscosity, poor fluidity of heavy oil can not be solved radically. This dissertation set out to deal with the problems caused by heavy component in reservoir development and carried out a further reserch on the thermolysis and viscosity reduction mechanism of asphaltene. It was a kind of technology with significance and practical value to develop heavy oil reservoir more efficiently.Composition, structure and thermal stability of asphaltene were detected by element analysis, infrared spectrum, nuclear magnetic resonance, and thermogravimetric analysis. The model experiment was carried out on the basis of presumed chemical structure model of asphaltene. With experimental data of 1H and 13C NMR, the average molecular formula and the structure parameters of basic structural unit of asphaltene were obtained, and the molecular models of asphaltene in crude oil of Liaohe, Daqing and Huabei were conjectured, which provided new methods and reliable basis for further studying the microcosmic structure of asphaltene.The pyrolysis mechanism of asphaltene under thermal recovery condition was studied. Thermal stability of asphaltene was emphatically studied by thermogravimetric analysis. The dynamics law was investigated in the thermolysis process, and DEMA of asphaltene in heavy oil from Daqing and Liaohe oilfields were established. It was shown that the breaking of bridged chain between thioether and fused ring and the breaking of side chain of fat structure unit result in reduction molecular weight of asphaltene. The latter was the major contribution to catalytic pyrolysis underground. The breaking of side chain and bridged chain of fat structure unit proceed as mechanism of ipso substitution. The introduction of active hydrogen in aquathermolysis reaction could capture free radical, which was beneficial to prevent the interlinkage of reactant chain, realizing the irreversible reduction of viscosity. The adding of hydrogen donor make it more effective to pyrolyze asphaltene and reduce viscosity of heavy oil. It was shown in thermogravimetric analysis(TG/DTG) that there were no obvious phenomena below 300℃; volatile substance was produced at a low rate between 300℃and 430℃; thermolysis mostly occured between 430℃and 550℃, and the peak temperature was between 470℃and 480℃.In near-critical water system, orthogonal experiments of catalytic pyrolysis of four asphaltene types from Liaohe heavy oil were carried out using nickel naphthenate and ferrous naphthenate as catalysts. The effects of reaction temperature, reaction time, catalyst amount on conversion rate of asphaltene were studied and the proper reaction conditions were obtained respectively. Under such conditions, sulfur contents of asphaltene were reduced obviously and it was found that the contents of carbon, hydrogen, oxygen, nitrogen also decreased in some degree. Because the breaking of C-C and C-H chemical bonds was less than that of other chemical elements, carbon and hydrogen contents increased slightly after thermolysis reaction. Due to diferent types of oxygen-containing groups contained in diferent asphaltene and less pyrolyzed mount of oxygen than other elements, oxygen contents of some types of asphaltene might increase in the contrary. In addition, it was found by infrared spectrum that the breaking of C-H chemical bonds on naphthenic and alkyl chains of pyrolyzed asphaltene was in different degree in near-critical water system. Aromatic rings and -CH2- were decreased as well.Through the study on water-rock reaction, it was proved that surface properties of oil reservoir minerals were changed after hydrothermal treatment. The formation of new minerals made its catalytic activity more active. Experimental results suggested that oil reservoir minerals have a catalytic effect on the thermolysis underground. The average molecular weight of asphaltene was reduced by 10% when adding 10% of oil reservoir minerals. The minerals also took synergetic catalysis action with Catalyst NiSO4, which could further reduce average molecular weight, increasing the molecular weight reduction ratio from 28.5% to 36.6%.On the basis of disaggregation of coal developed by Olah, Catalytic pyrolysis experiment of asphaltene by super acid were carried out by using heavy oil samples from Liaohe oilfield. It was shown that HF:BF3 was a high efficient chemical agent to pyrolyze and light asphaltene.According to above results and combining thermal recovery conditions in the field, experimental study on application of asphaltene for thermal recovery engineering of heavy crude was carried out. The new scheme proposed was to make use of asphaltene in thermal recovery engineering of heavy crude. The steam was produced by the energy from incomplete combustion of asphaltene, and the burning residue was used to prepare high effective steam additive. The results of laboratory experiment show that burning residue of asphaltene in heavy oil from Huanxiling oilfield could be used as steam additive while that from Shanjiasi oilfield was useless.