A comparison of rock physics models for fluid substitution in carbonate rocks

Rock physics models play a crucial role in seismic reservoir characterisation studies. The optimal rock physics model for a sandstone reservoir might be significantly different from that of a carbonate reservoir. There are several theories that compare the elastic properties of dry and saturated rocks. These models have mainly been explained by poroelastic theories or effective medium theories. The Gassmann's model which is commonly used in petroleum rock physics is suitable for rocks with spherical and interconnected pores at low frequencies. These assumptions do not necessarily meet the conditions of carbonate rocks. In this work, two additional models, the differential effective medium (DEM) model and the self-consistent (SC) model have been examined for several carbonate samples. Ultrasonic 30 carbonate and 5 sandstone core samples from an oil field in south-west Iran were measured in the laboratory. The results show that the DEM model gives the best compatibility with the dense and low porous carbonate samples. These results are confirmed by well log data from the same area.