Rock physics analysis is a useful tool in time-lapse seismic feasibility studies and can help to assess the effect of pressure and saturation changes on the elastic parameters which the seismic data is sampling and hence the probability of success of a 4D seismic survey. Calibration using velocity measurements made on dry core data at varying pressure conditions allows for forward modelling of the expected seismic response at different effective pressures as well as different hydrocarbon saturation levels. The step of forward modelling the pressure changes is performed less frequently and in a less well calibrated manner than that of changing the hydrocarbon saturation as there is often no core data analysis performed at different pressures.
In this study we show that incorporating pressure effects produces non-negligible changes to the elastic properties of the reservoir rock. Changes of up to 10% and 8% to acoustic and shear impedance respectively are observed in the most prospective reservoir interval when the pressure effect is included. Such changes would be detectable by high quality 4D seismic data. The authors recommend including the pressure change data whenever possible in 4D rock physics modelling.