Abstract: The low resistivity oil reservoirs in Banqiao Oilfield have apparent different response features in logging curses from normal oil reservoir.Through the analysis of geology and clay minerals of Banqiao Oilfield,an integrated study on the causes of the low resistivity reservoir is made.From the study,it can be concluded that the hydrophilicity of rocks which have thinner sizes and higher clay contents is the main cause of low resistivity reservoir.The stratum in Ban-qiao oil field mainly consists of siltstones and fine sandstones which have a high shale content.The high shale content clays fill the pore of grain.The pore type which is mainly pore-throat makes free water incapable of flowing freely in the finer pore-throat.As a result,the upper content bound water is formed.On account of clay mineral，the intergranular pore of oil formation is rebuilt and it makes the pore diameter lessening and tiny pore developed.Additionally，because of the violent absorption ability of montmorillonite，a great deal of water is absorbed into the surface of particles and clays.At the same time，the migration of looser kaolinites leads to the jam of pore-throat which makes part of free water bound water.This makes the bound water content even higher in the oil formation.
The secondary causes which lead to the formation of low resistivity reservoir are the additional conductive function of clay mineral,the thinner thickness of reservoir and mud invasion .

Key words: low resistivity oil reservoir, shale content, bound water, genetic mechanism