Research On Mechanism And Application Of Downhole Viscosity Reduction Upgrading Of Heavy Oil

This paper taking Liaohe oilfield extra heavy oils,under the simulated thermal recovery condition,fundamental experiments were carded out in the high temperature high pressure CWYF-â… type reactor to study the viscosity reduction upgrading behavior of heavy oil.Based on laboratory results,the mechanism of viscosity reduction upgrading was revealed,the viscosity reduction chemical system was selected optimally and tested on field.1.Results from reaction of viscosity reduction subjected to high temperature water showed that the optimum condition for Liaohe heavy oil to occur aquathermolysis were: reaction temperature 240℃,reaction time 24h,water adding amount 30wt%.Water at high temperature of 300℃owned the property of solvent,which was nearly equivalent to the solvent property of acetone at 25℃.Water could act as both of acid catalyst and alkali catalyst.2.Viscosity reduction upgrading reactions with catalyst were investigated.Four kinds of transition metal catalysts were prepared,and oil-soluble organic nickel salt C1 was selected optimally to be used in the viscosity reduction reaction experiments.At the same reaction condition of 240℃,24h and 30wt%water,compared to the reaction without catalyst,the viscosity reduction ratio of oil sample from the reaction with 0.1wt%catalyst C1 increased about 30%,and the Contents of asphaltene and resin decreased 1.4wt%and 5.0wt%relatively,while the aromatic and saturate increased with a value of 3.5wt%and 2.9wt%.The content of element C in the heavy oil reduced,while the value of element H increased,resulting in the increasing of H/C ratio.The ratio of heteroatom to carbon reduced.3.IR spectrograms of heavy oils before and after viscosity reduction reaction showed that the introduction of catalyst caused the heavy oil to occur decarboxylation reaction. Structure change of asphaltene was detected from the TG-DTA of asphaltene in heavy oil before and after catalyzed viscosity reduction reaction,part of asphaltene changed into paraffin-soluble matter.The mechanism catalyst played in the viscosity reduction reaction process could be summarized as:activate the reactants,speed up the hydrogenation reaction rate and increase the conversion rate of hydrogenation reaction.Catalyst might form chemisoptive bond with hydrogen molecular,change the fragmentation pathway of hydrogen molecular,reduce the activation energy between hydrogen molecular and free radical,accelerate the hydrocracking of heavy oil organic molecular.4.Catalyzed viscosity reduction upgrading reactions with hydrogen donor were investigated.Formic acid was selected optimally from the alternative chemicals of tetrahydronaphthalene,dihydrogenanthracene,formic acid and methylformate,and its dosage was 7wt%.Compared to the oil sample from reaction without hydrogen donor,the light components increased,the heavy components reduced obviously.The contents of asphaltene and resin decreased and that of the aromatic and saturate increased.The value of H/C ratio of heavy oil increased.The content of element S in the heavy oil reduced,the structure of heavy oil changed,viscosity reduced.5.IR spectrograms of heavy oils before and after reaction with hydrogen donor showed that the structure of asphaltene in heavy oil changed.TG-DTA curve of asphaltene in heavy oil showed that the thermostability of asphaltene weakened.The mechanism hydrogen donor played in the viscosity reduction reaction process was to supply hydrogen to deactivate part of the free radicals,decreasing its concentration in the reaction system,so as to inhibit the condensation reactions.6.Viscosity reduction upgrading reactions with auxiliary agent were investigated.Urea was selected optimally from the alternative chemical auxiliary agents of ammonium carbonate,urea and ammonium hydrocarbonate,and its dosage was 20wt%.Compared to the oil sample from reaction without auxiliary agent,there was no obvious change on group compositions,the contents of atom C,H,S,N and O nearly kept unchanged.As a result,the introduction of urea did not change the structure of heavy oil.The structure was influenced mainly by the catalyst and hydrogen donor.7.Infrared spectrum analysis on heavy oil and asphaltene in it before and after viscosity reduction reaction with auxiliary agent showed that there was no significant change on the absorption peak of functional group of heavy oil.Namely,the introduction of auxiliary agent basically did not change the structure of the heavy oil and asphaletne.Gas chromatographic analysis on the saturate indicated that after the reaction,part of the long chain cracked into short chain,increasing the content of light hydrocarbons.Thermal analysis on asphaltene showed that the thermostability of asphaltene in heavy oil after reaction with auxiliary agent weakened.Nuclear magnetic resonance spectra showed that the peaks atδ_c14.10,δ_c22.67,δ_c28.98 andδ_c31.92ppm were ascribed to alkyl carbon;the peak atδ_c14.10 was ascribed to the CH₃ carbon bonding with the secondary carbon atom; the peak atδ_c19.73 was ascribed to the CH₃ carbon bonding with the quaternary carbon atom;the peaks atδ_c22.67,δ_c28.98,δ_c31.92ppm were -CH₂- carbon atom;the peak atδ_c128.21ppm were ascribed to the carbons in the aromatic ring. 8.Stability test on heavy oil after catalyzed reaction with hydrogen donor and auxiliary agent showed that the viscosity rebounding rate was no more than 3%.The addition of auxiliary agent had not only some degree of viscosity reduction function,but also synergistic interaction to the catalyzed reaction with hydrogen donor.9.The mechanism of urea assisted steam flooding was that the CO₂ and NH₃ generated by the thermal decomposition of urea at high temperature would supply reservoir energy rapidly,and NH₃ would react with the naphthenic acid,long chain fatty acid,etc.in the crude oil,forming surface active soap-like materials,which had positive effect on the viscosity reduction.Part of CO₂ will dissolve in oil,make it swell,reduce its viscosity, increase the internal kinetic energy;other CO₂ will fill the formation pores,enlarge the steam sweep area,which is helpful to recover oil.10.It was revealed that there existed competitive reactions in the viscosity reduction reaction process.The simplified chemical model of competitive reaction was brought forward,which provided the basis to study deeply the downhole viscosity reduction upgrading of heavy oil.11.Field tests of downhole viscosity reduction upgrading were carried out on three representative oil wells of Du32-53-33,Shul-32-41 and Qi40-03-18 in Liaohe oilfield.In the initial 15 to 20 days of the test period,the viscosity reduction ratio of heavy oil was higher than 70%,and the value kept above 60%within 30 days.Chemical composition analysis on heavy oil after upgrading process indicated that the content of asphaltene and resin decreased and that of the aromatic and saturate increased,which further identified that it was feasible to recover heavy oil by downhole viscosity reduction upgrading technology.