Chang-7 member of the Triassic Yanchang Formation is rich in oil and composed of organic-rich shale and tight sandstone.The shale serves both as source rock to nearby tight sandstone and as reservoirs.An improved appreciation of pores and fracture networks in the shale and tight sandstone reservoirs is of great significance to understand storage space characteristics and migration mechanisms of shale oil and tight oil.Through qualitative description and quantitative chara-cterization

pore types and pore size of the organic-rich shale and tight sandstone were studied by comprehensively utilizing methods including core description

field emission scanning electronic microscope

laser scanning confocal microscopy

nuclear magnetic resonance

high pressure Hg injection

and low-temperature thermal adsorption.Organic-rich shale contains intragranular pores

intergranular pores and organic pores

with most pore size less than 50nm.It also contains micro-fractures.Horizontal

low angle

high angle and vertical fractures can all be observed in the shale.The tight sandstone contains residual primary intergranular pores

inter-crystals pores and secondary pores (the major type).Pore size is mostly larger than 2 μm and pore-throat size is less than 73.5 nm.However

pore-throats that contribute the most to improving permeability are those ranging between 73.5 nm and 735 nm.Microfractures and high angle fractures can also be spotted in the tight sandstone.Forming and evolution of pores both in shale and tight sandstone are suggested to be controlled by sedimentation and diagenesis.Migration and charging of diagenetic fluids and hydrocarbon fluids worked toge-ther to forge organic-rich shale and tight sandstone into an organic whole.The study also distinguishes three kinds of pore and fracture networks and pathway of oil migration in shale and tight sandstone of the Chang-7 member:①nonameter-micrometer pores- fracture networks in organic-rich shale (acting as storage space and migration pathway within source rocks);②nanometer pore throat-micrometer pores-fracture networks in tight sandstones (acting as storage space of tight oil);③differential pore throat structure-microfracture-fracture networks between shale and tight sandstone(acting as migration pathway for oil from source rocks to outside reservoirs).