Poroperm analysis,
mercury injection capillary pressure (MICP),
and nuclear magnetic resonance (NMR) measurements were performed to
delineate the pore structures and fractal behaviors of the Eocene
low-permeability sandstones in the Dongying Depression, Bohai Bay
Basin, China. Three types of pore structures (I, II, and III) have
been classified by applying the self-organizing map (SOM) clustering
model. Comparative analysis of three different fractal models indicates
that the MICP tubular model and NMR model are quite effective for
pore structure characterization. The results show that the reservoirs
generally exhibit high fractal dimensions, indicative of complex pore
structures. The presence of small pore throats is primarily responsible
for the heterogeneities and complexities in the Eocene low-permeability
sandstones. A modified Winland model was established for the permeability
estimation using MICP data. Different from high-permeability reservoirs
or unconventional (e.g., shale and tight formation) reservoirs,
r
10
is the best parameter for permeability estimation,
indicating that the permeability of the Eocene low-permeability sandstones
is largely controlled by the large pore systems. Additionally, a porosity
model derived from movable fluids using NMR data has been established
and provided better prediction effect compared with the classic Coates
and Schlumberger Doll Research (SDR) models. Fractal analysis and
permeability estimation are shown to be quite effective for investigating
microscopic behaviors and in predicting the reservoir quality of low-permeability
sandstone reservoirs.