Source rocks formed in lacustrine fault basins are strongly heterogenous.The Dongying sag is one typical representative of the continental fault basins with the major source rocks including the Upper Es

4

Lower Es

3

and Middle Es

3

members of the Paleogene Shahejie Formation deposited in saline water and fresh water environments.Based on the analysis of sedimentary facies and organic features

a comparative study of the residual hydrocarbon yields and hydrocarbon generation potential indices between the ordinary source rocks (TOC

<

2%) and high quality source rocks (TOC

>

2%) for the three members of Shahejie Formation was performed to understand their differences in hydrocarbon expulsion mechanisms and efficiencies.As they are different in depositional environments and buried depths

their hydrocarbon generation-expulsion potentials and efficiencies are significantly differe-nt.In comparison with the ordinary source rocks

the high quality source rocks are the main contributor to hydrocarbon accumulation.They not only can generate abundant hydrocarbons

but also can expulse hydrocarbons efficiently thanks to their microstratifications.In addition

hydrocarbon expulsion models were built for source rocks deposited in different environments.The source rocks that were deposited in saline water environment generate hydrocarbons in two stages

i.e.immature and mature stages and expulse hydrocarbons in longer period and higher efficiencies.In contrast

the source rocks that were deposited in fresh water environment only generate hydrocarbons in mature stage and feature in shorter hydrocarbon expulsion period and lower expulsion efficiencies.The Upper Es

4

Member has the greatest contribution to hydrocarbon pooling

followed by the lower and middle Es

3

members.