In order to demonstrate the genesis of low permeability reservoir of nearshore subaqueous fan in northern steep slope of Dongying sag

abundant cores and reservoir analysis data were utilized to conduct the research on lithological characters of reservoir

diagensis

diagenetic sequence and porosity evolution as well as their controlling factors.The sandbodies of nearshore subaqueous fan of the Shahejie Formation consist of arkose and feldspathic lithic sandstone and the reservoirs have experienced strong compaction

carbonate cementation

dissolution of calcite and feldspar in the burial diagenetic evolution.The reservoirs are at the middle diagenetic stage now

have a burial depth in the range of 1 700-3 500 m and mid-low porosity(mean porosity 11.3%)and low permeability(mean permeability 23.12×10

-3

μm

2

).The strong compaction and carbonate cementation reduced the porosity and permeability of the reservois

while dissolution contributed to the improvement of reservoir quality.The intergranular pores and intragranular pores resulted from dissolution of calcite and feldspar at the depth of 2 900-3 200 m are constructive to reservoir quality(porosity up to 25% and permeability up to 1 000×10

-3

μm

2

).Obviously

identification of dissolution and intervals with well-developed secondary pores is extremely important for predicting favorable reservoir.