In order to better study the characteristics
of the pore structure
and to explore the influence factors of its fractal dimensions during
the thermal evolution of oil shale, the immature oil shale (
T
max
= 433 °C, TOC = 28.00%) of the Ordos
Basin Extension Group was selected to simulate the whole thermal evolution
process from immature to over mature in a semiopen system. Organic
geochemical data show that the thermal simulation hydrocarbon generation
threshold is between 300 and 400 °C. According to AIP-SEM observation,
the pore types of the samples are different in different thermal simulation
stages. The fractal dimensions are calculated by low-temperature N
2
adsorption data using the fractal Frenkel–Halsey–Hill
fractal model. The average surface fractal dimension (
D
1
) is 2.26, indicating that the pore (<4 nm) surface
is relatively smooth. The average pore structure fractal dimension
(
D
2
) is 2.49, indicating that the pore
(>4 nm) structure is complex. Through the exploration of the relationship
between fractal dimensions and organic geochemistry, whole rock X-ray
diffraction, and N
2
adsorption data, it is found that fractal
dimensions have different degrees of correlation with thermal maturity,
mineral composition, TOC content, and pore parameters. Through comprehensive
research, it shows that hydrocarbon generation and expulsion, oil
and gas cracking, and organic matter carbonization have important
effects on the pore structure and fractal characteristics of oil shale.