Molecular Composition Of Coke Precursor And Coke Formation Mechanism In The Simulated In-situ Combustion Process For Oil Recovery

In-situ combustion（ISC）is well recognized for its high efficiency to recover heavy oils.In-situ combustion is considered to be a strategic receiving technology of heavy oil mining in Xinjiang oilfield.Although numerous studies have been reported that oil properties exhibit significant changes during the ISC,the reaction mechanisms and the evolution of oil components are still not well understood.In this paper,the reactor was used to simulate pyrolysis of the Hongqian crude oil in Xinjiang,and the pyrolysis experiments under different reaction conditions were designed to realize the understanding of the laws of cracking and coke formation.The compounds of produced oils were characterized at the molecular level using gas chromatography with mass spectrometry（GC-MS）and high-field Fourier-transform ion cyclotron resonance mass spectrometry（FT-ICR MS）to realize the understanding of the laws of cracking and coke formation.The Hongqian crude oil in Xinjiang had high acid number and viscosity.Relative content of cycloalkanes was abundant and were dominated by 2-4 cycloalkanes.Cycloalkanes with short side chains was relatively less.Olefins can be detected during atmospheric pressure pyrolysis.Olefins were not detected and pyrolysis oil with high DBE under high pressure.The composition and yield of coke could be affected by the change of gas atmosphere.Under oxygen atmosphere,coke was generated at 350℃and the mass ratio of oxygen element in coke is as high as 5%.The presence of H₂O increases the mass ratio of nitrogen and oxygen elements in coke.The yield of coke was the highest and the H/C of coke was the lowest in CO₂ atmosphere.While CO₂ could promote the condensation reaction of crude oil and inhibit cracking.The composition of petroleum hydrocarbons changed with the reaction time.In the early stage of the reaction,a large amount of hydrocarbons were generated due to the cracking reaction of petroleum acid,and resulted in a relatively high content of petroleum hydrocarbons with low carbon numbers.As the reaction time increases,small molecular gaseous hydrocarbons generated during cracking reaction,which were discharged from the reactor,and the relative content of petroleum hydrocarbons with high carbon number increased in the liquid phase.