Organic matter reservoir space of shale in Dongying Sag, Bohai Bay Basin

The contribution of hydrocarbon conversion to reservoir space of the shale in the lower Es3 and the upper Es4 in the Dongying Sag of the Bohai Bay Basin is discussed according to the volume change of kerogen in the process of hydrocarbon generation.It is proposed that the two sets of shale is of high brittle mineral content,and the mechanic property of the shale changes obviously in the depth intervals of 2 000-3 000 m and the shale becomes more brittle.There are good preservation conditions for pores within organic matter below 3 000 m,and the porosities within organic matter of the two sets of shale with different organic matter abundance in different buried depth are further discussed.It is shown that the porosities within organic matter are very limited for the shale with low abundance of organic matter(TOC content 2%);however,for the shale with higher abundance of organic matter(TOC content 4%),the porosities formed during hydrocarbon generation process can reach 4% in the higher mature stage.In the Dongying Sag,the upper Es4 section has a higher maturity,and the porosities within organic matter are widely developed during hydrocarbon generation in the deep depression.For comparison,it has a much lower organic maturity and porosity,and only locally developed in the lower Es3.