The continental shale oil potential is remarkably huge in China

but the current production of shale oil is much less than expected.Therefore

in order to reveal the geochemical characteristics and shale oil accumulation mechanism of organic-rich shales

a multiple geochemical techniques

mainly including total organic carbon (TOC)

Rock-Eval

organic maceral and gas chromatography mass spectrometry (GC-MS)

were systematically performed on a total of 50 shale samples from shale oil field in the Biyang Depression

Nanxiang Basin

in this study.On the basis of the diversities in the color

structure and microscopic characteristics

two types of shales have been identified

which are black laminated shale (type A) and gray shale (type B

including gray shale

dark mudstone and few silty mudstones)

respectively.The testing results show that (1) type A

mainly formed in high salinity and strong reducing environment

is rich in TOC (up to 8.59%) and algea organic matter (AOM) with kerogen of type Ⅰ

and contains plenty of the horizontal cracks favorable for shale oil storage which have enhanced the abundant oil content (high free hydrocarbon S

1

and chloroform bitumen "A" concentrations) at present

resulting that the enriched shale oil resources occurred in this type of shales;(2) type B

mainly developed in weak reduction environment with low salinity

has less TOC abundance (low to 1.09%) with kerogen of type Ⅱ and poor AOM contribution

and vertical cracks within shales have accelerated the hydrocarbon expulsion

which has led to today's poor oil content and resulted that this type of shales only contains potential and ineffective shale oil resources.Thus

the type A of shales can effectively generate and store abundant shale oil

which is of great reference value for further exploration and development of shale oil in the future.