Sandstone reservoir rock physics modeling and time-lapse seismic analysis

Time-lapse seismic analysis can be used to monitor changes in reservoir parameters over time as the development progresses. The physical parameters of reservoir, such as porosity and water saturation, will undergo changes with the development of the oil field. Theoretical rock physics models establish the relationship between reservoir petrophysical parameters and reservoir elastic parameters. We propose a petrophysical parameter substitution method based on variable critical porosity rock physics model to further analyze the impact changes in reservoir petrophysical parameters on the elastic parameters (P -wave velocity, S -wave velocity and density) of the reservoir. Porosity substitution and fluid substitution can accurately characterize the changes the elastic parameters of rocks with variations in petrophysical parameters. The method of controlling variables is employed during rock physics substitution, when substituting one type of petrophysical parameter, the other petrophysical parameters should remain unchanged. By using rock physics inversion, it is possible to invert the critical porosity from velocities of reservoir. Afterward, we substitute petrophysical parameters: porosity and water saturation, by comparing and analyzing the seismic wave velocities and seismic characteristics before and after substitution, we can analyze the impact of changes in reservoir petrophysical parameters on seismic. The test results from theoretical model and well logging data indicate that the rock physics substitution method can be applied to differentiate the influences of reservoir petrophysical parameters such as porosity and water saturation on reservoir elastic parameters and seismic characteristics.