Advancing fluid saturation calculations through integrated reservoir pressure adjustment and heterogeneity evaluation, iranian offshore carbonates

This study examines the combined influence of reservoir pressure and heterogeneity on water saturation estimation. The analysis focuses on carbonate reservoirs of the Persian Gulf region. A total of 58 limestone samples were analyzed for formation resistivity factor, with 20 also tested for resistivity index. Cementation factors were determined at surface and reservoir pressure (5700 psi), enabling water saturation calculations. Experimental validation employed Dean-Stark extraction on 160 core samples. Water saturation calculations without rock typing yielded averages of 47% under surface conditions and 97% under reservoir conditions, significantly overestimating water saturation. By applying the Winland and flow zone indicator rock typing methods, water saturation was reduced to approximately 37% and 56% (Winland), and 38% and 58% (flow zone indicator) for surface and reservoir conditions, respectively. These predictions closely match the average water saturation of approximately 20% obtained from Dean–Stark experiments. This emphasizes the role of heterogeneity and pressure effects in petrophysical analysis. Specific cementation indexes were calculated for each rock type to better represent in situ conditions, further improving fluid saturation modeling. The main novelty of this study lies in the integrated analysis of reservoir pressure effects and rock typing classifications for improving water saturation estimation in heterogeneous carbonates.