The Es

3

shales in Dongpu Sag were studied with XRD analysis

thin section and SEM observation

and low-temperature nitrogen adsorption experiment based on their basic geochemical characteristics.Microscopic characteristics of shale pores were analyzed

and thus controlling factors of shale pore development and its significance for hydrocarbon retention in shales have been identified.Results show:the Es

3

shales in Dongpu Sag can be classified into silty shales

calcareous shales and gypsum shales according to their mineral compositions;the strong heterogeneity in shales'geochemical characteristics reflects a complex hydrocarbon retention pattern in Es

3

shales;several pore types including interparticle

intraparticle and organic-matter pores and fractures

are identified in Es

3

shales with different lithologies dominated by different pore types;the pore systems in Es

3

shales can be dominated by micropores

macropores

or pores of multiple diameters based on low-pressure nitrogen adsorption experiment;pore development in Es

3

shales is affected by both deposition and diagenesis

with deposition environment laying the foundation for pore development in various lithologies and diagenesis modifying pore structures during shale burial

respectively;oil and free gas mainly accumulate in large pores and microfractures

and micro-and meso-pores provide sites for adsorbed gas

while solution gas is of great significance to develop shale oil/gas resources.