Study On Coke Formation Process And Mechanism Of Liaohe Heavy Oil During In Situ Combustion

In situ combustion(ISC)process is one of the most efficient and economical heavy oil recovery technology.As coke is the main fuel of the burning front,the coking characteristics of heavy oil in the ISC are very important.In the process of the ISC,there is an obvious lowtemperature oxidation zone,and the pyrolysis coking characteristics of heavy oil after lowtemperature oxidation will change significantly,but there are still few reports about it.In addition,the research on the ISC coke produced from Liaohe heavy oil is lacking.Therefore,this paper studied the formation process and mechanism of the Liaohe heavy oil coking and provided basic data and theoretical support for the implementation of the ISC.The coking process of Liaohe heavy oil by low-temperature oxidation and pyrolysis reaction was studied in this paper.The coking characteristics of heavy oil under different reaction temperatures were firstly studied,and then the influence of low-temperature oxidation on pyrolysis coking was investigated.The composition changes of the products under different reaction parameters were analyzed using the FTIR,the elemental analysis and the scanning electron microscope.The thermochemical properties of coke were studied using a TG-DSC,and the suitable coke and coking conditions for the ISC were explored.Finally,by calculating the kinetic parameter of coking reaction and comparing the composition changes of product and tail gas before and after the experiment,a new understanding and supplement to the mechanism of heavy oil coking were proposed.It could be found from the low-temperature oxidation experiment that the coke yield of heavy oil was 6.39～19.88%,the oxygen content of low-temperature oxidation coke was more than 9.7%,there are C=O,C-O,and other oxygen-containing functional groups in coke.The ignition temperature of low-temperature oxidized coke was between 456.4～484.0°C,and the heat value was between 16445～27169J/g.The coke yield,ignition temperature and heat value increase with the increase of oxidation temperature.It could be found from the pyrolysis coking experiment that the low-temperature oxidation reaction would change the composition of heavy oil,so it had a great influence on the pyrolysis coking reaction.The coke yield of heavy oil after low-temperature oxidation was increased by11.7-38.5%.The oxygen content of crude oil and oxidized heavy oil pyrolysis coke was less than 4%,and the oxidized heavy oil coke had a denser microstructure.The ignition temperature,burnout temperature and peak temperature of coke from oxidized heavy oil were higher than those of crude oil,indicating that low-temperature oxidation modification made the activity of coke worse.This paper comprehensively compared the characteristic of low-temperature oxidized coke,pyrolysis coke from crude oil and pyrolysis coke from oxidized heavy oil.Pyrolysis coke from crude oil has moderate coke yield,high heat value and high comprehensive combustion characteristic index,which is conducive to the establishment and steady advance of the combustion front.It is the most suitable fuel for the ISC.The low-temperature oxidation process will lead to the degradation of fuel performance in the combustion front,so the occurrence of low-temperature oxidation reactions should be reduced in the ISC process.