The deep sandstone of delta

fan delta and fluvial fan facies are low porosity low permeability or mid porosity low permeability reservoirs with filling micropores and intragranular pores.In general

the intragranular porosity decreased with the increasing of sandstone burial depth;the secondary enlargement of quartz

the filling of chlorite and kaolinite

the cementation of iron calcite and iron dolomite reduced the porstiy;solution in deep strata resulted in large amount of eroded pores.Late diagenesis could be divided into A

B and C diagenetic substages.Considerable organic acids in A substage caused solution pores in feldspar and debris;in the B substage

CH

4

and CO

2

existed

chlorite filled the pores

thus preserved micropores and solution pores;in the C substage

organic acids decreased and CH

4

CO

2

increased

thus forming fractures and improving reservoir property.