Is Gassmann the Best Model For Fluid Substitution In Heterogeneous Carbonates

Fluid substitution is used to predict potential changes in seismic due to production in oil reservoirs. Gassmann’s model has been successfully applied to 4D-time lapse seismic in clastic reservoirs. However, the applicability of this model in carbonates is not well understood. To evaluate alternative models, we compare Gassmann, Generalize Gassmann, and Patchy saturation models in a carbonate reservoir in the Middle East. We estimated seismic changes due to substitution of oil by water after 5 and 18 years of production. We found that Gassmann’s model generally predicts the lowest seismic variation. Therefore, a 4D-time lapse seismic would not be recommended here, according to Gassmann’s model. Generalized Gassmann’s model results corroborates that seismic response depends on porosity type. Finally, Patchy saturation model shows favourable results for a 4D-time lapse seismic in both studied scenarios. Consequently, if we are going to use 4D-time lapse seismic as a production management tool in this type of carbonate reservoirs we need more information about pore structure and saturation distribution.