Abstarct: The variation of seismic signal properties which depends on the amount of oil production and fluid replacement in reservoir, can provide re-measurement of seismic data. The objectives of this study is to investigate the relationship between different rock physics models for one of the oil fields in the Persian Gulf sandstone reservoir. Then the effects of fluid substitution on compressional wave velocity, shear wave velocity and density are calculated. Finally the changes of seismic signal properties in seismic forward modeling is studied. The results of this study indicate that the Gassmann rock physics model and the improved lower and upper boundaries of Hashin-Shtrikman average model, can be taken as an appropriate rock physics models for calculating of the dry bulk modulus of the selected reservoir. In addition, the results show the fluid substitution in two different scenarios is more than 10 percent change in compressional wave velocity for the Gassmann model of homogeneous saturation, while it is less than 1 percent in hetrogeneous saturation for both wells of W_1 and W_2. The determination coefficient between compressional wave velocity values of the Gassmann and the improved lower and upper boundaries of Hashin-Shtrikman models in W_1 and W_2 wells was determined 0.825 and 0.696 respectively. The mean square error was also estimated 0.089 and 0.113 respectively for these wells. So it is concluded that the average of the upper and lower boundaries of the improved Hashin-Shtrikman model baxsed on the Hertz-Mindlin theory is an appropriate model for this reservoir. According to the considered scenarios for fluid substitution and the results of seismic modeling, it can be concluded while the amount of reservoir oil production reaches to the 15 percent of its insitu value and when 10 percent gas is substituted for the produced oil, the seismic signal amplitude at the top of the reservoir can be increased due to the reduction of the compressional wave velocity and due to this effect seismic survey can be done again. It will be possible when reservoir fluid distribution is homogenous. Otherwise, if reservoir saturation is hetrogeneous type, for more oil production, the seismic operation will be provided other time. The results of seismic attributes for fluid substitution indicated that among the amplitude envelope, the first derivative of amplitude envelope, the second derivative of amplitude envelope, the quarter amplitude and the sweetness attributes, the sweetness and the amplitude envelope attributes are able to show the fluid substitution adequately.