Unambiguously determining irreducible water saturation \(\left({S}_{\rm{wirr}}\right)\) poses a formidable challenge, given the availability of multiple independent methods. Traditional approaches often depend on semi-experimental relationships derived from simplified assumptions. These methods, originally designed for oil sandstone reservoirs, result in varying \({S}_{{\text{wirr}}}\) values when employed in carbonate gas reservoirs. Nuclear magnetic resonance (NMR) is the most advanced technique for determining \({S}_{{\text{wirr}}}\) . While highly accurate, the NMR-based method necessitates the laboratory measurement of the transverse relaxation time \(\left({T}_{2}\right)\) cutoff. Laboratory-based \({T}_{2}\) cutoff determination is resource-intensive and time-consuming. This research aims to develop a robust model for determining \({S}_{{\text{wirr}}}\) in carbonate gas reservoirs by utilizing NMR well logging measurements and special core analysis (SCAL) tests. Various \({T}_{2}\) cutoff values were initially employed to compute bound water saturation \(\left({S}_{{\text{bw}}}\right)\) at different depths to achieve this. Subsequently, the data points \(\left({T}_{2}, {S}_{{\text{bw}}}\right)\) were graphed on a scatter plot to unveil the relationship between \({S}_{{\text{bw}}}\) and \({T}_{2}\) . The scatter plot illustrates an exponential decrease in \({S}_{bw}\) with increasing \({T}_{2}\) , forming the basis for the \({S}_{{\text{wirr}}}\) model derived from this relationship. Finally, the parameters of the \({S}_{{\text{wirr}}}\) model were fine-tuned using SCAL tests. Notably, this \({S}_{{\text{wirr}}}\) model not only accurately yields \({S}_{{\text{wirr}}}\) at each depth but also offers a dependable determination of the optimal \({T}_{2}\) cutoff for the reservoir interval.
