<p>Quantification of isolated vuggy porosities in carbonate reservoir aids in more accurate calculation of porosity, water saturation and hydrocarbon in place. This study proposes a novel approach to identify and estimate the isolated vuggy porosity and its impact on gas volume calculations in carbonate reservoirs with a case study from one of the giant carbonate gas reservoirs of the Dehram Group in southern Iran. Three key wells were selected and analyzed to study the impact of isolated porosities on volumetric calculations. The vuggy porosity was investigated and confirmed using thin sections, image logs and conventional petrophysical logs. To understand the presence of isolated vugs, Serra's cross-plot was employed. The total porosity from the neutron density logs and the acoustic logs for the primary porosity were calculated. The pore type was determined by a velocity deviation log and confirmed by core measurements. Isolated vuggy porosity was determined and compared to the isolated vuggy porosity obtained using the Lucias’s method. The cementation factor was calculated and integrated with the core data. Water saturation with two approaches, the presence and absence of isolated vuggy porosity, was investigated to determine its quantitative impact on petrophysical evaluation. Results show that quantification of isolated vuggy porosity reduces average effective porosity from 12 to 10.4%, increases water saturation from 13.3 to 40.8%, and decreases hydrocarbon column thickness by 22%. Analysis of three key wells reveals that isolated vuggy porosity and thickness decrease from northwest to southeast, correlating with improved reservoir quality. The study highlights the significant influence of isolated vuggy porosity on petrophysical evaluations and volumetric calculations.</p>