Permeability Estimation of Tight Sandstone based on Dual T2 Cutoff Value Model and Fluid Substitution

We propose a dual T2 cutoff value model to elaborate the storage mechanism and the seepage law of fluid in tight sandstone. We divide the pore space into three parts. Relationships between permeability and percentages of different pore intervals are investigated and then an empirical model is presented to estimate the permeability. A self-adaptive method of determining dual T2 cutoff value is obtained by applying the second order difference of the T2 spectrum. We also propose a fluid correction algorithm to construct the water spectrum of in-situ NMR data, aiming to eliminate the influence of oil on the magnetization and enhance the precision of downhole application of the new model. Field application in a tight sandstone reservoir indicates that the improved method provides better performance than conventional models such as Schlumberger-Doll Research equation andTimur-Coates equation.