Reservoir characteristics study is very important to understand the hydrocarbon potential of organic-rich shales.A series of analyses and tests

including thin sections

SEM

XRD

physical property

total organic carbon(TOC)

specific surface area and pore size distribution

were made to reveal the reservoir characteristics of the organic-rich shales of the Triassic Yanchang Formation(Fm)in Ordos Basin.This paper also defined the lithofacies

mineral types

diagenesis

pore types and physical properties.Three types of lithofacies are identified in the organic-rich shales

including muddy shale

silt-bearing shale and silty shale.The muddy shale has the highest TOC content

clay content of more than 50% and relatively weak diagenesis.The dominant pore types of the organinc-rich shales in the Yanchang Fm are intragranular and intergranular pores.The pore sizes of micropores are mainly within 0.4 to 1 nm and those of mesopores are mainly within 3 to 5 nm.The contribution of the mesopores to pore volume and specific surface area is larger than that of the micropores.The high content of ductile minerals and weak diagenesis of the organic shales in the the Yanchang Fm make the reservoir stimulation more challenging.