Abundant lacustrine shale oil resources have been discovered
in
the Eocene saline lake system, Yingxiongling Sag, Qaidam Basin. Compared
with the Cretaceous Qingshankou Formation in the Songliao Basin and
Triassic Chang 7 Member in the Ordos Basin, the lithofacies of Yingxiongling
shale are more complex, featuring thinner single-layer and faster
vertical variations. How to establish a reasonable lithofacies classification
and evaluate the effectiveness of different lithofacies is the key
to unlocking the giant resources of Yingxiongling shale oil. Based
on the total organic carbon analysis, rock pyrolysis analysis, fluorescence
thin section observation, oil saturation analysis, helium porosity
measurement, high pressure mercury intrusion by scanning electron
microscopy, focused ion beam-scanning electron microscopy, and nitrogen
adsorption analysis, the organic geochemistry, reservoir property,
and oil-bearing property were comprehensively analyzed. This paper
proposed a lithofacies classification scheme of Yingxiongling shale
oil and systematically evaluated the quality of representative lithofacies.
The key findings were as follows: (1) Eight types of lithofacies were
identified based on the rock structure and mineral composition, namely,
thin-bedded/laminated dolomitic limestone, thin-bedded/laminated limy
dolostone, thin-bedded/laminated mixed rock, thin-bedded sandstone,
and laminated shale. (2) The types and combinations of lamination
varied greatly among different lithofacies. Dolomite primarily formed
through calcite shrinkage during the dolomitization process, resulting
in the formation of abundant intercrystalline pores. (3) More organic
matter was observed in the calcite laminae, which was deposited as
a result of small calcite particle flocculation. (4) The combination
of laminated dolomitic limestone and thin-bedded limy dolostone formed
a favorable source–reservoir assemblage, which was the pay
zone for horizontal wells. These understandings could further be helpful
in understanding shale oil enrichment in the Qaidam Basin and could
provide scientific guidance and technical support for the exploration
and development of global plateau shale oil.