Mechanism Study On Combustion Kinetics And Pyrolysis Of Heavy Oil In Fire Flooding

Heavy oil has great potential to be the next strategic energy in China.Fire flooding technology has been shown as a promising technology for the heavy oil recovery.While it is critical to keep substantial fuel and air injected to sustain the continual combustion in the fire flooding process.So,study of fuel deposition process should be more significant than the project design and economy evaluation.In this paper,the heavy oil sample is separated into four frictions firstly,and analyzed by elemental,density,viscosity,heat value analysis and infrared spectrum.The physico-chemical properties of heavy oil are confirmed by in-depth analysis.Through the kinetics experiments of heavy oil combustion and pyrolysis,we compare the reaction process and kinetics behavior of heavy oil sample in air and nitrogen atmosphere.The results show that heavy oil goes through four stages in air atmosphere: initial stage,low temperature oxidation stage,fuel deposition stage and high temperature oxidation stage,but only initial stage and degradation stage in nitrogen atmosphere.And reaction activation energy in both atmosphere shows the same trend,it increases in the beginning then decreases with increasing of temperature.But the peak values and their corresponding temperatures are different.Through the mechanism experiments of heavy oil combustion and pyrolysis,we summarize the reaction mechanism of combustion and pyrolysis through comparing the transformation law of infrared spectrum structures of heavy oil and product structures.Meanwhile,we also study the influence of the exist of sandstone core.The results show that reaction rates under air atmosphere in different reaction stages are always faster than under nitrogen atmosphere.And an obvious induction period is observed under nitrogen atmosphere,which is not existed in air atmosphere.At the same time,sandstone core shows the obvious catalytic effect on fuel deposition stage.Finally,after summarizing the results of kinetics experiments and mechanism experiments,we concluded the reaction path of heavy oil combustion and pyrolysis.Then we infer the applicable reaction mechanism of heavy oil combustion and pyrolysis in two reaction atmosphere.In the air atmosphere,heavy oil sample experiences the oxygenation decarboxylation process to form the heavy hydrocarbon.Then it is transformed into coke with low H/C ratio and high aromatic structure.Subsequently,the coke is combusted and releases huge heat.Under nitrogen atmosphere,cracking and polymerization play a leading role in different reaction stages respectively.And the coke is separated out since it reaches the solubility limit of asphaltene.Then the coke cracks into micro-molecules structures under high temperature.