The Study Of Pores Evolution Of Shale And Shale Oil Mobility Evaluation In North Songliao Basin

In recent years,with the rapid development of unconventional oil and gas exploration and development,shale oil has become an unconventional oil and gas resource with rapid development and great potential after shale gas.However,due to the extensive development of a large number of micro-nano pores and complicated pore structure,traditional research methods are difficult to characterize their complex pore structure.At the same time,the study about the occurrence state of shale oil in shale pore system and the evaluation of shale oil momentum are still very weak.This paper takes the shale of the north Songliao Basin as the research object.For the shale samples with different thermal evolution,through the basic experimental analysis and reservoir space characterization experiments,the related research on the characteristics of shale reservoir,pore structure,pore type division and pore structure evolution were carried out.The occurrence state of shale oil in the study area and its influencing factors were clarified by molecular dynamics simulation method.The mobilization and distribution of shale oil in the study area were evaluated by logging method.The results show that the pore morphology of the shale is dominated by the “ink bottle” type pores.Secondly,it also contains a partial conical slit pore and a peaceful plate slit pore.Scanning electron microscopy revealed that the pore types of shale are mainly organic pores,intergranular pores and intragranular pores,and more interstitial pores are developed.The pores were divided into four types of pores: macropores(>150nm),mesopores(150?50nm),small pores(50?10nm)and micropores(<10nm)by mercury intrusion method combined with fractal theory.The total pore size distribution of shale was evaluated by NMR experiments,and the pores are mainly micro-pores.The main pore size distribution range is between 3?50nm,and the pore type of the shale in the Nenjiang Formation is worse than that of the Qing-1shale.With the increase of the degree of evolution,the porosity of the shale in the study area increased first and then decreased,and the peak of the increase in porosity corresponds to the peak position of hydrocarbon generation.The pore volume of organic matter in the shale of the study area increases with the degree of evolution,and the organic matter gradually disappears to form an organic-matrix shrinkage joint with the degree of evolution.The organic matter developed between the pyrites gradually disappears with the degree of evolution to form a large number of pores.The clay minerals,especially the chlorite gradually developed,and organic acids are produced along with the evolution of organic matter,resulting in a large number of dissolution pores.The pore evolution model of shale was established by quantitative analysis of different types of pore evolution characteristics and two-dimensional characterization by scanning electron microscopy.The occurrence characteristics of shale oil were revealed by molecular dynamics simulation.It was found that the adsorption density peak and adsorption thickness remained unchanged when the pore throat size was larger than 4 nm.The adsorption capacity of clay minerals on shale oil increased with the increase of temperature gradually weakened.With the increase of the carbon number of normal paraffin,the adsorption amount per unit area gradually increased,indicating that the heavy components have stronger adsorption capacity on the surface of clay minerals.The adsorption capacity of shale oil is different for different mineral lattices.According to the shale oil volume per unit area obtained by molecular simulation combined with the pore size distribution of shale,the shale oil adsorption free ratio was evaluated.It was found that the proportion of free shale oil in the shale of the Qing-1section was 45% higher than the average of the Nenjiang group.The limit of movable oil in the shale of the Qing-1 section of the study area is 75mg/g·TOC by the empirical method,and the Nenjiang Formation is 100mg/g·TOC.The distribution of shale oil mobility in shale reservoirs in the study area was obtained by combining the organic heterogeneity evaluation method of logging.