Abstract：At the present time,reservoir waterflooding technique is widely applied to third-time oil recovery.The key to this new technique lies in determining correctly waterflooded area and monitoring the location and movement situation of waterflood front in reservoir.Forward modeling shows that under certain condition gravity logging method can be used to map the waterflooded area and to know the location and movement situation of the waterflood front in reservoir.By applying accurate gravity lagging method to the sandstone reservoir whose porosity is above 15%and where the variation rate of water saturation may be higher than 50 0 o,we can monitor both the moving waterflood front within 50m from observation borehole and the moving direction variation of waterflood front in the 120 degree fan area whose symmetric axis passes injection borehole and observation borehole.
