To better understand the development characteristic of nanopores and its geological controlling factors

we collected 11 shale samples from the Taiyuan

Shanxi

and Yanchang formations in the Weibei

southeastern Ordos Basin

and performed low-temperature nitrogen adsorption

Argon-ion milled and field emission scanning electron microscopy(FE-SEM)

vitrinite reflectivity(R

o

)and maceral composition

total organic carbon(TOC)content and X-ray diffraction(XRD)analyses.The selected shale samples are in the transition period from low mature to mature

and are quite different in TOC.The nanopores in the shales are dominated by pores within the size of 2~50 nm

which account for 63.5% of the total pore volume.The BET specific surface area is commonly higher than 10 m

2

/g

indicating a favorable condition for methane adsorption.The pore types are mainly of narrow-slit pores and ink-bottle shaped pores.The dominant mineral compositions are different from area to area:clay minerals being dominated in the Hancheng area

while brittle minerals being dominated in the Tongchuan area.Clay mineral content is positively correlated with the total content of nanopores smaller than 2 nm and that within 2-50 nm

while the brittle mineral content is positively correlated with the content of nanopores larger than 50 nm.This means that the difference in mineral types is the main control factor on the development of nanopores.Moreover

R

o

and TOC also have some influences on the development of nanopores.The higher the R

o

is

the higher content of large nanopores is

but the lower content of medium to small nanopores is.In addition

the higher the TOC

the higher content of medium to small nanopores is.