Upgrading Of Heavy Oil In Supercritical Water

In the process of oil extraction,with the continuous attenuation of natural layer energy,the heavy components in tertiary recovery wells,which are of low liquidity and high viscosity,will deposit to form organic sediments under the effect of disturbance factors,such as the changes of temperature and pressure,and block the crude oil seepage channel with the reducing of single well production.In order to deal with the blocking in down-hole zones,energetic materials,such as solid rocket propellants,were utilized to fracture the recovery layers to reopen the flowing channels.The combustion of propellant charges can increase the temperature of the burning area,which can not only improve the dissolving ability of crude oil on heavy components but also transfer the water near the burning area into supercritical water.Thus,the heavy sediment was upgraded and the unblocking was achieved finally.In order to better understand the cracking mechanism and dynamics of heavy oil cracking in supercritical water,the organic monomolecular n-hexadecane was used to study the pyrolysis process as a model compound in the temperature of 380,400,420℃.The distribution of pyrolysis products were analyzed by gas chromatography and gas chromatography-mass spectrometer.Taking consideration of literatures,the comparatively detailed pyrolysis mechanism of free radicals was obtained to explain the reaction phenomena and results.It was confirmed that the pyrolysis reaction of organic materials are first order reaction in supercritical water.The thermal cracking reaction activation energy of n-hexadecane is 202 kJ/mol,the pre-exponential factor is 1.770E+13 min^-1.In order to further simulate the actual conditions of the physical and chemical process during the combustion of energy material,the upgrading of the crude oil in supercritical water was studied in an autoclave.The changes of oil composition were studied under the condition of the temperature（380,400,420℃）,the time（0.5,1,2,3h）,the density of water（0.05,0.10,0.15,0.20 g/cm³）and the water-oil ratio（1:1,2:1,3:1 and 4:1 g/g）.The changes of ratio and structure of four components in heavy oil before and after the cracking were analyzed.It is concluded that the optimum reaction conditions of heavy oil cracking in supercritical water were 420℃,1 h among the scope of this research.With the existence of supercritical water,the heavy components（resins and asphaltenes）in oil could be cracked into small molecule compounds with higher liquidity and dissolvability.It could be concluded that the organic sediments near the wellbore area could be upgraded with high efficiency and the removing of organic sediments and unblocking could be achieved.The influence of changing water density and water-oil ratio during the cracking process was studied in supercritical water.The mechanism of phase structure changing was proposed in the process of pyrolysis mechanism.With the increasing of supercritical water in the system,the pyrolysis process could be changed from two phase structure into pseudo-homogeneous phase and the cracking process was enhanced with the formation of coke suppressed.A five-lumped dynamic model was proposed to study the dynamics of heavy oil thermal cracking in supercritical water,which consists of saturated hydrocarbon,aromatic hydrocarbon,resins,asphaltenes and coke.The kinetic parameters were obtained through the calculation programs,and it was proved that the dynamics model had a high degree of fitting.The dynamic model can be used to predict the change of the constituent contents of heavy oil during upgrading in any supercritical conditions and estimate thermal chemical effect of energetic material in well-bore area.