Multiple heterogeneity characteristics and evolutionary process of the Lower member 3 of Paleogene Shahejie Formation lacustrine shale in the Bonan Subsag

Jiyang Depression have been analyzed based on previous sequence stratigraphic framework and analysis of core observation and sample testing.The results show that the Lower Es

3(下)

can be described as a third-order sequence

which can be divided into expanding systems tract (EST)

early highstand systems tract(EHST) and late highstand systems tract (LHST).Lithofacies associations

mineralogy

algae species occurrence

as well as TOC (total organic carbon) and kerogen type

change noticeably and regularly in the Lower Es

3

shale within the sequence stratigraphic framework.For lithofacies associations

six lithofacies are identified.From the EST to the LHST

there are increased abundance in clay minerals

quartz and feldspar

and reduced abundance in calcite and dolomite

while pyrite reached the highest abundance in EHST.Algaes have the largest number and most variety of species in the LHST.TOC content is the lowest in the EST.Kerogen type is dominated by type Ⅰ and Ⅱ

1

.The oil richness is influenced by multiple heterogeneity characteristics

comparative analysis suggests the EHST is the most potential shale oil target interval in the study area with excellent oil richness.