Understanding the content, component
features, and controlling
factors of hydrocarbons in different occurrence states is a key element
in assessing the resource potential, mobility, and engineering exploitability
of shale oil. X-ray diffraction, bulk geochemistry, multi-isothermal
stage pyrolysis experiments, and total hydrocarbon chromatographic
analyses were performed on a set of muddy siltstone (MS), fine sandstone
(FS), dark mudstone (DM), and black shale (BS) from the Chang 73 subsection in the Huachi area to investigate the content,
component features, and controlling factors of hydrocarbons in different
occurrence forms and estimate the shale oil engineering producibility
under different production technical methods. The results show that
the residual hydrocarbon content in FS, BS, MS, and DM decreased in
turn. Mudstone and shale (Mu&Sh) samples featured lower quartz
and chlorite contents as well as more pyrite and mixed layer I/S than
siltstone and sandstone (Si&Sa) samples. Free and weakly adsorbed
hydrocarbons constitute the mainstay of the hydrocarbons in BS and
DM, while free hydrocarbons were dominant in MS and FS. The pyrolytic
gases were chiefly CO2 and methane. The (Sat. + Aro.)/(Res.
+ Asp.) ratios and plagioclase and chlorite contents jointly show
a positive effect on the free/adsorbed hydrocarbon ratios, while the
TOC, clay mineral, and mixed layer I/S contents were inversely proportional.
In general, geochemical features and mineral composition chiefly affect
adsorbed hydrocarbon yields to control the free/adsorbed hydrocarbon
ratio, the only exception of which is that the (Sat. + Aro.)/(Res.
+ Asp.) ratios affect free hydrocarbon yields. Si&Sa has good
shale oil resource potential under volume fracturing because of its
relatively high free hydrocarbon and brittle mineral contents and
gas oil ratio. The weakly adsorbed hydrocarbons in Mu&Sh will
be better transformed to the free state under pyrolysis conditions
at 400 °C, which is more suitable for in situ heating conversion
production. This study provides a new reference and basis for the
occurrence and mobility evaluation of Chang 73 shale oil
under different exploitation methods.