Pore Structure And Fluid Micro Distribution Of Middle And Low Mature Continental Shale

Great progress has been made in shale oil and gas exploration in middle and high maturity stage,while shale oil in middle and low maturity stage is difficult to flow due to high viscosity and strong polarity of crude oil.The study of pore structure and fluid distribution of medium and low mature shale plays an important role in the evaluation of oil and gas mobility and analysis of development potential of medium and low mature shale.In this paper,the geochemical and mineralogical characteristics of oil shale samples from the upper member of Jiufotang Formation and Shahai formation in Ludong sag of Kailu Basin were analyzed,and the pore structure of fluid containing/removing samples with different particle sizes was compared by low temperature N₂ adsorption.The results show that the shale of upper Jiufotang Formation and Shahai formation has high organic carbon content,and the kerogen types are mainly type II and type II?III,which are in the low medium mature hydrocarbon generation stage and are good source rocks.There are many small pores in the sample,and the pore morphology is mainly tabular pores.At the same time,a certain number of macropores are also developed in the shale.With the decrease of shale particle size,the maximum adsorption capacity and the measured specific surface area increase.The micropores increase slightly,the smaller mesopores(<10nm)decrease,while the larger mesopores(>10nm)and macropores increase greatly.With the decrease of particle size,the isolated pores in the sample are exposed,and more and more pores can contact with the particle surface to form a connection.However,excessive comminution will also destroy some of the original pores in the sample.For the samples of kerogen type I,?and?-?,the content of chloroform asphalt"A"is higher,and with the decrease of sample size,the relative content of small molecules such as saturated hydrocarbon and non-hydrocarbon increases.The content of chloroform asphalt"a"in kerogen type III samples is low,and the content of components extracted from different particle size samples is similar.For kerogen type I samples,the specific surface area,total pore volume,micropore volume,mesoporous volume and macropore volume of large particle size samples increased after extraction,while the total pore volume and macropore volume of small particle size samples decreased after extraction.For type II and type II-III samples,the specific surface area,total pore volume and micropore volume increase,the mesoporous volume increases and decreases,and the macropore volume decreases as a whole.Moreover,the macropore volume of shale samples with smaller particle size decreases more after extraction;The specific surface area,total pore volume and pore volume of each pore size of kerogen type III decreased after extraction.By fitting the variation of pore structure parameters with the content of organic matter components,it is found that the variation of specific surface area,total pore volume and micropore volume of shale has a good positive correlation with the content of saturated hydrocarbon,which shows that the pores of shale are dominated by medium and small pores,and the extracted movable hydrocarbon preferentially occupies the medium and small pores,and the content of saturated hydrocarbon is relatively high.The proportion of non-hydrocarbon macromolecules in larger pores is higher.