<![CDATA[Recent developments in petroleum industry have been -witnessing the surge of the use of nuclearmagnetic resonance (NMR) log. Despite some remaining problems the NMR technology appearsto gain more acceptance as petrophysical tool for evaluating reservoir quality. Comprehensiveformation evaluation requires determination of irreducible fluids, movable fluids, and permeabil-ity. Hoyvever, rock heterogeneity introduces complexity in any formation evaluation activities.This can also cause problem for NMR log interpretation. In the presence of clays the most com-monly used T, cut off values, a constant value throughout a formation, seem to eventually yieldinaccurate irreducible yvater saturation estimates, as yvell as other output such as permeability.This study focuses at finding a solution for finding the best way of choosing the most representa-tive T, cut off value to be used in NMR log interpretation. This is indeed a common pressingproblem for heterogeneous formation rocks such as in the case of Tirrawarra sandstones used inthis study. The main part of the study is devoted to comparison between the use of single aver-aged T,c value and establishment of empirical correlations enabling the provision of T,c for anylevel of heterogeneity (i.e. various levels of shaliness). The study hoyvever surprisingly shoyvsthat, in spite of the theoretical soundness of the empirical correlations established, simple aver-aging of T,c values yielded by a reliable method proves itself adequate. This conclusion thereforehelps considerably in reducing complexity in NMR log interpretation. Key yvords: T,e irreducible yvater saturation, ductile components, empirical correlation, aver-aged T2c]]>
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