Abstract: Core observation,thin section identification,X-ray diffraction,physical property and organic matter testing are integrated to reveal the mineral composition,physical properties,organic matter and lithology of the shale oil reservoirs in the Lower 3^rd Member of Shahejie Formation in Zhanhua Sag,the Bohai Bay Basin.And the characteristics of pore types and structure and their influences on reservoir property are analyzed by using Argon-ion milling and scanning electron microscope (SEM) technique.The mineral compositions of the target strata are dominated by clay,carbonate and terrigenous clastics.Both the porosity and permeability are low.The kerogen belongs to type I with high total organic carbon (TOC) content in the range of 0.52%~9.32% and vitrinite reflectance (R_o) in the range of 0.7%~0.93%.The lithologies are dominated by argillaceous limestone,limy mudstone and mud bearing limestone,with minor limy dolomite.With Argon-ion milling and SEM method,we studied 10 core samples from Well Luo 69 via qualitative analysis and quantitative statistics.According to the pore characteristics,pores can be divided into micropores and microcracks.The micropores can be further subdivided into intergranular pore,intercrystalline pore,dissolved pore and intracrystalline pore.The microcracks,dissolved pores,large intercrystalline pores and intergranular pores provide the main reservoir space for the shale oil reservoir.Pore types and distribution vary with different reservoir lithologies,which control the reservoir storage capacity.The limy dolomite is the best in storage capacity,followed by limy mudstone,argillaceous limestone and mud bearing limestone,and the limestone is the least.

Key words: Argon-ion milling, SEM, pore structure, shale oil, Zhanhua Sag