Study On The Densification Mechanism Of The Second Member Of Xujiahe Formation In Anyue Area

The 2th member of Xujiahe Formation in Anyue Area is typical low permeability tight sandstone reservoir.Based on the method of Oil Geology,Reservoir Geology,Sedimentology,and Oil&Gas Geochemical,combined with experimental technology such as core observation,microscopic rock section observation,conventional mercury injection,scanning electron microscopy,electron probe,fluid inclusions and so on,the paper studed reservoir petrology characteristics,diagenesis,reservoir diagenetic evolution and reservoir densification mechanism.Research suggests that the reservoir sand gives priority to feldspar lithic sandstone,and time of lithic sandstone of the 2th member of Xujiahe Formation.Affected by various source system,the type of debris is also in many styles,but is mainly hard cuttings for the repeatedly washing under the action of wind and waves.The same reason,study area has better reservoir particle separation,high psephicity,less mixed base content,as well as high textural and composition maturity.The pore type is mainly composed of feldspar and debris,and the residual intergranular pores are mainly in local.Reservoir porosity is concentrated in 7%?-9%,average 8.9%.permeability is mainly concentrated in 0.01mD-0.1mD.It is typical low porosity,low permeability tight reservoir..The reservoir sandstone has experienced complex diagenesis.It is in the middle diagenetic B sub period now.According to the thin section observation and determination of trace besides porosity evolution elements that the porosity is reduced to about 10%at the end of late Jurassic,and the reservoir has been basically densification.To a certain extent,the latter dissolution improved the porosity of reservoir,but it is worse again because of the second silica and calcite cementation.The clay mineral such as autogenous illite more seriously blocked the pore roar,and the reservoir permeability was greatly reduced.In the end,it becomes today's tight reservoir.The composition,particle size,content of the clastic particles and space distribution in the study area are controlled by sedimentation,so it is the basic factor affecting the physical properties of the reservoir.On the other hand,diagenesis is the final cause of reservoir density.Compaction,silica cementation and a small amount of calcium cementation cut the porosity a lot,while illite and other clay minerals seriously blocked the pore roar,and ultimately lead to the tight reservoir.