Determination of nuclear magnetic resonance T2 cutoff value based on multifractal theory — An application in sandstone with complex pore structure

ABSTRACTThe cutoff value of nuclear magnetic resonance (NMR) transversal relaxation time T2 is vital for pore structure characterization, permeability prediction, and irreducible water saturation calculation. Conventional default values often lead to inaccurate results for rocks with complex pore structure. Based on NMR experiments and multifractal theory, we have developed an effective statistical method to predict T2 cutoff values without other petrophysical information. The method is based on multifractal theory to analyze the NMR T2 spectrum with the assumption that the T2 spectrum is an indicator of pore size distribution. Multifractal parameters, such as multifractal dimension, singularity strength, and mass exponent, are calculated to investigate the multifractal behavior of T2 spectrum via NMR experiments and a dyadic scaling-down algorithm. To obtain the optimal T2 cutoff value, the rotation speed and time of centrifugation are enlarged increasingly to optimal centrifugal state. A predicating mod...

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