Research on T2 Cutoff-value Determination Method for Shaly Sand Based on Experiments

The determination of NMR T2 cutoff-value is one of the most important sections in laboratory analysis as well as in practical nuclear magnet resonance logging data analysis.And nowadays,most researchers usually adopt the centrifugation method or experienced value method to determine T2cutoff value.However,these two methods have great limitations in practical logging.Based on the seepage characteristics of shaly sand and Coates-cutoff model,established is T2 cutoff calculating model of dispersed shaly sand.The NMR T2,cutoff has relation with rock porous structure and seepage feature;Distribution range for the T2,cutoff of the shaly sand is wider.A theoretical model of T2,cutoff and QV has been obtained from permeability model analyses.The T2,cutoff the shaly sand continuously decreases with the increases of QV.The above result indicates that the T2 cutoff and QV has a relationship of power function and the exactly T2 cutoff value can be predicted by this model,which has a significant meaning for extensively analysis of nuclear magnet resonance logging.How to calculate accuracy QV should be considered in practical logging.