Abstract: The water flooding in the oilfield can cause the change of not only reservoir fluid saturation, but also reservoir temperature and pressure. These variations pose the different influences on the seis-mic velocity, and can be reflected on the time-lapse seismic profile.For analyzing and discussing the alone or integrated variety laws that temperature, pressure and saturation of water function cause, this paper makes full use of the Biot-Gassmann equation, and combine the other experiential formulas to get the volume modulus of fluid and the elastic modulus of rock. Throughthe study of the variety law of the velocity of sandstone strata of Bohai oilfield, its results will help us to acknowledge the time-lapse seismic monitoring technique,and improve the ability of recognizing the oil-pool’s change of the time-lapse monitoring in the area.

Key words: time-lapse seismic monitor, reservoir temperature, reservoir pressure, saturation of water, seismic velocity