Feasibility of 4D-seismic Studies of Sarvak Reservoir in Azadegan Field

The present study is concerned about monitoring 4D seismic of Azadegan oil field; Sarvak formation is a major reservoir and supposed to be the prospect formation At first، 31 plug samples taken from cores and all of the Sarvak formation limestone were sent to the Japan National Oil Corporation’s Technology and Research Center (TRC) for laboratory measurements of P and S wave velocities in the reservoir conditions and at different amounts of fluid saturation، pressures، and temperatures. Moreover، the porosity of core samples and petrophysical data were studied and measured at RIPI. Afterwards، seismic responses of Sarvak formation were analyzed from two points of view، namely velocity and amplitude، and their changes in relation to reservoir conditions were modeled and analyzed. Then، to examine the validation of Gassmann’s equation، laboratory core samples were used. The results reveal that the Gassman’s model with a relative error of less than 4% provides acceptable data for the studied reservoir. The results of this study show that changes in the effective pressure will lead to 12% changes in compressional wave velocity and 21% variation in shear wave velocity. Such a change in reflection coefficient of compressional wave velocity is equal to 6%. However، changes induced by manipulating saturation were less than 2% which had low validity in seismic monitoring. Therefore، the probability of imaging the changes due to fluid displacement is insignificant and it is not successful for monitoring the studies of reservoir internal changes. However، simultaneous changes of pressure and fluid displacement on compressional seismic data (present seismic data) are estimated about 13%، which means that it is possible to interpret such changes. Thus it is suggested conducting 4D seismic monitoring during the Azadegan development program for the Sarvak reservoir fluid and studying pressure changes.