Investigating NMR T2-Cutoffs: Towards better reservoir Characterization

This study focuses on the importance of accurately determining the T2 cutoff value, a crucialpetrophysical parameter that differentiates movable fluid from immovable fluid in formations. Standard T2cutoff values (33 ms for sandstones, 100/200 ms for carbonates) may not apply uniformly across a column,leading to discrepancies in saturation determination. Accurate T2 cutoff determination, typically done in thelab, is time-consuming and expensive. The goal of this study is to correlate T2 cutoff to the T1/T2 ratio andsaturation using NMR data alone. Cores from sandstones and carbonates were used and NMR T2 and T1T2measurements were performed at various water saturations for each core sample. The findings show averagecutoff values of 119 ms for carbonates and 26 ms for sandstones. Correlations were established between T2cutoff and water saturation, T2 cutoff and T1/T2 ratio, and T1/T2 ratio with water saturation. Thesecorrelations, based solely on NMR data, can be applied to logs when T2 cutoff data from cores isunavailable. The study demonstrates strong correlations between T2 cutoff, irreducible water saturations,and the T1/T2 log mean ratio, confirming the relevance and applicability of these correlations for downholedata.