Research On Mechanism Of Ultrasound Assisted Low Temperature Catalytic Aquathermolysis Of Ultra-heavy Oil

Ultra-heavy oil, whose notable features are its high viscosity and poor mobility, accountsfor a large proportion of world proved oil and gas reserves. Generally, ultra-heavy oil isproduced by steam injection technology, but the thermal efficiency is usually low and the oilviscosity is easy to restore, which will lead to the increasing difficulty of artificial lift andsurface delivery, thus severely restricting the high-efficient development of the reserves.Therefore, exploration of technology and method to reduce the viscosity of ultra-heavy oilirreversibly during the production will be of great significance. Recently, developingtechniques of catalytic aquathermolysis and ultrasonic visbreaking of heavy oil have donesome helpful researching in this area, and have gotten a certain achievement. The combinationof ultrasonic treatment and catalytic aquathermolysis is a new attempt to reduce heavy oilviscosity, and it is hopeful to take advantage of the synergistic effect between ultrasonic andcatalyst to lower the reaction condition and deepen the reaction extent of aquathermolysis ofheavy oils at relatively low temperature.Based on the multi-subject theories of ultrasonics and chemistry, in this paper, the basicissues of ultrasound assisted low temperature catalytic aquathermolysis of ultra-heavy oilwere systematically studied, the controlling factors and influencing mechanisms of thiscomposite technology were revealed, and the aquathermolysis mechanisms and reactionkinetics were also studied. The main achievements obtained are as follows:On the basis of the study of rheological properties, compositions and molecularstructures of Binnan ultra-heavy oil, the influencing rules and influencing mechanisms of themulti-factors, such as ultrasonic frequency, ultrasonic intensity et al., on the viscosityreduction rate of ultra-heavy oil after ultrasonic treatment are revealed by single factorexperiments. According to the design thought of combining the inorganic metal ions havinghigh catalytic activity with long chain organic matters, a novel difunctional catalyst, whichnot only has multi-catalytic centers but also owes the hydrogen precursor, was preparedsuccessfully, and the influencing rules and mechanisms of ultrasonic parameters and catalystic aquathermolysis parameters on the viscosity reduction rate of ultra-heavy oil treated byultrasonic cooperated with chemical were studied. In addition, synergistic effect of ultrasonicand catalyst was investigated by comparing the effect of the same influencing factor on theviscosity reduction rate of heavy oil with and without chemicals. Meanwhile, theexperimental results indicated that ultrasonic visbreaking and ultrasound assisted lowtemperature catalytic aquathermolysis of ultra-heavy oil both have preferable universality andcan reduce heavy oil viscosity irreversibly.By means of modern chemical testing and analysis techniques, the rheological properties,compositions and molecular structures of Binnan ultra-heavy oil before and after ultrasonicvisbreaking and ultrasound assisted low temperature catalytic aquathermolysis reaction werecompared, thus, heavy oil viscosity reduction mechanisms of the both techniques were studied,and part of the possible reaction pathways of ultra-heavy oil visbreaking were revealed.Experimental results indicated that, after ultrasonic treatment, the content of saturates andaromatics increased, while the content of resin and asphaltene decreased; the average relativemolecular weights of ultra-heavy oil and its group components all decreased; heteroatomcontent in heavy oil and its heavy content reduced, and hydrogen-to-carbon ratio increased;peak number of saturated hydrocarbon in gas chromatogram increased, and the content ofhydro carbons with large carbon number decreased. The results of IR spectrum analysisproved the changes in functional group number and molecular structures of heavy oil. Theresults of nuclear magnetic resonance analysis indicated that aromatic carbon rate of heavycontent decreased, while aromatic condensation degree and carbon chain branching indexincreased. GC/MS results indicated that various micromolecule hydro carbons andheteroatom-containing compounds were found in the gas and water after treatment. All theabove results proved that ultrasonic can break the macromolecule in heavy oil, and prompt thetransform of heavy content into light hydro carbons, thus effectively reduce the viscosity ofheavy oil and improve its quality, the main reaction types may include bond breaking,hydrogenation, heteroatom removing, dealkylation, ring-opening, dealcoholization,depolymerization and isomerization et al.. Ultrasonic visbreaking mechanisms of heavy oilcan be summarized as ultrasonic cavitation, hydrogenation reaction, dilution effect of lightdydrocarbon, reduction of Van der Waals force, ultrasonic mechanical vibration and thermaleffect.Compared to ultrasonic vibreaking, ultrasound assisted low temperature catalyticaquathermolysis further increased the light component content, hydrogen-to-carbon ratio,aromatic condensation degree, carbon chain branching index, and the content and types of micromolecule hydro carbons and heteroatom-containing compounds in the reaction gas andwater, meanwhile, it decreased the heavy component content, average relative molecularweights, heteroatom content, and aromatic carbon rate of heavy oil. The more subduedcharacteristic absorption peak in IR spectrum of heavy oil and its heavy content showed thatthe synergistic effect of ultrasonic and catalyst prompted the bond breaking, hydrogenation,heteroatom removing, dealkylation, ring-opening reaction of heavy oil. The appearance ofnew product in gas and water indicated that synergistic effect has broadened the visbreakingpathway of heavy oil. Mechanisms of ultrasound assisted low temperature catalyticaquathermolysis of ultra-heavy oil can be summarized as catalytic aquathermolysis, ultrasoniccavitation, synergistic effect of ultrasonic and catalyst, hydrogenation reaction, dilution effectof light dydrocarbon, reduction of Van der Waals force, ultrasonic mechanical vibration andthermal effect. Ultrasonic can provide energy for chemical reaction and improve catalystactivity, thus promotes heavy oil catalytic aquathermolysis reaction and accelerates thecatalytic aquathermolysis rate. Catalytic action can change the molecular structure anddecrease the molecular activation energy of the oil, thus helps to bring into play the viscosityreduction effect of ultrasonic. In short, synergistic effect between ultrasonic and catalyst mayaccount for the improvement of catalytic aquathermolysis degree and effect.The results of kinetic study of sonochemical decomposition of thiophene indicated thatsynergistic enhancement factor of ultrasonic and catalyst is about3.48, and the reaction is afirst-order kinetic process. Decomposition dynamics models were established according to thedecomposition pathway of thiophene, and the kinetic constants were obtained by solving themodels, the study results showed that the calculation of reactant and product concentrations fitin well with the experimental results. In addition,5-lump kinetic models of ultrasoundassisted low temperature catalytic aquathermolysis of ultra-heavy oil were built, and thekinetic constants of the5lumps were obtained by data fitting with experimental results,afterwards, the5lumping kinetic models were solved using Runge-Kuta method, it is foundthat the calculation results tally well with the experimental results. Kinetic study shows thatultrasonic visbreaking, catalytic aquathermolysis and ultrasound assisted low temperaturecatalytic aquathermolysis of ultra-heavy oil have different dynamics processes. Ultrasoniccooperate with catalyst can launch some reactions that difficult to occour under singleultrasonic or catalyst conditions at low temperature. It can be concluded from the values ofthe kinetic constants that resin is a kind of fairly active reactant, and it is the main reactioncenter during the aquathermolysis reaction of ultra-heavy oil.The studies above indicated that the technology of ultrasound assisted low temperature catalytic aquathermolysis is feasible. The combination of ultrasonic and catalyst has asynergetic function to the reaction, which attributes to the reduction of viscosity andimprovement of quality of heavy oil. However, as a new technology, there are still numerousquestions unsolved. The next key research directions in the future should be the investigationof visbreaking processes and mechanisms of heavy oil in micro-time scale, and the devicedevelopment and process design of the amplification experiments.