Permeability calculation for glutenite reservoirs based on variable T₂ cutoff value in nuclear magnetic resonance...

Due to the strong heterogeneity of glutenite reservoirs, conventional well logging or nuclear magnetic resonance (NMR) logging alone often fails to achieve satisfactory evaluation results. In this study, we propose a method to evaluate the permeability of glutenite reservoirs with a variable T₂ cutoff value. First, the shale content of the glutenite reservoir is determined from conventional well logs. Then, based on the data of core porosity-permeability analysis, the relationship between shale content and the comprehensive pore structure index I (hereinafter referred to as I) is established. This I is calculated from core porosity and permeability data. Using the relationship between I and the T₂ cutoff value, the T₂ cutoff is determined and subsequently incorporated into the COATES model to evaluate reservoir permeability. Importantly, this method does not rely on costly core laboratory measurements such as mercury injection, centrifugation, or NMR experiments. Evaluation results show that the average error between the permeability obtained by this method and the core-measured permeability is reduced from 65.3% (SDR model) and 64.7% (COATES model) to 12.5%, while the correlation coefficient increases from 0.37 (SDR model) and 0.22 (COATES model) to 0.65. These results indicate a significant improvement in evaluation performance.