Influence Of Sub/Supercritical Water Pyrolysis On The Nanostructures Of Paleogene Jijuntun Formation Oil Shale In Fushun Basin

As an important part of unconventional resources,oil shale is considered as an important replacement of traditional oil resources,and has great advantages in resource reserves,development potential,etc.Underground in-situ conversion of oil shale is a cutting-edge technology in the current research field of oil shale.There are mainly two types of in-situ mining methods:conduction heating and fluid heating.However,the current mining method is mainly for shallow buried reservoirs,which is difficult to apply to the in-situ mining of deep oil shale buried more than 1000m.In view of the portability,fracturing and extraction characteristics of high-pressure supercritical water,it has become the research direction of deep oil shale in-situ mining.The evolution of oil shale nanostructures is the basis for exploring the oil and gas production mechanism of sub/supercritical water pyrolysis,and has important theoretical and scientific significance for improving the development and utilization of deep oil shale in-situ injection of sub/supercritical water.For this reason,this thesis takes oil shale of Jijuntun Formation of Paleogene in Fushun Basin as the research object,and conducts pyrolysis experiments of oil shale in three ways of anhydrous（electric heating）,near critical water and supercritical water through high-temperature and high-pressure Source rock pyrolysis simulation device.The differences of oil shale microstructure under three pyrolysis modes are analyzed through scanning electron microscope.On this basis,the variation characteristics of different chemical groups of oil shale under three pyrolysis modes were characterized by advanced 13C-NMR solid-state nuclear magnetic resonance and X-ray photoelectron spectroscopy（XPS）;Based on low-temperature nitrogen adsorption technology and using multifractal theory,the evolution characteristics of nano pore structure and heterogeneity under different pyrolysis methods were studied.Based on the above work,compared with traditional anhydrous pyrolysis,the evolution laws of chemical structure and nano pore structure under near critical water and supercritical water pyrolysis methods have been explored.The main research findings are as follows:（1）Compared to anhydrous pyrolysis,sub/supercritical water at the same temperature:（1）enhances the degree of organic matter pyrolysis,promotes the formation of a large number of intergranular pores in organically derived minerals,synchronously increases the content of organic-inorganic pores,increases the pore size,and enhances the connectivity between pores of different origins;（2）The synergetic evolution of minerals is promoted,and the proportion of mixed layer minerals of Yimeng is increased,which makes it easier to increase the nano pores in oil shale.（2）Advanced ¹³C-NMR and XPS results show that compared with anhydrous pyrolysis,sub/supercritical water pyrolysis reduces the fat carbon content of kerogen in oil shale at the same temperature,and the condensed ring condensation phenomenon is enhanced,and the aromatic carbon rate is increased,thus improving the oil and gas production rate of oil shale and promoting the generation of more nano scale organic pores.（3）The low temperature N₂ adsorption experiment results of samples before and after chloroform extraction showed that:（1）At 300℃-360℃,the residual oil in the pores of the pyrolytic oil shale reduced the pore volume and specific surface area of nano pores,and the residual oil mostly existed in pores<30 nm;（2）Compared with anhydrous pyrolysis,at the same temperature,the pores of the 3-30 nm pore size of oil shale increase significantly after sub/supercritical water pyrolysis;（3）The pore size distribution of oil shale has multifractal characteristics.Sub/supercritical water pyrolysis improves the balance of porosity distribution in each pore section,enhances the correlation between porosity clusters in oil shale,and contributes to the migration and accumulation of produced oil and gas.