Abstract: In the eastern oil fields of the South China Sea, when using nuclear magnetic resonance(NMR) logging to calculate the permeability of low porosity, low-permeability light oil reservoirs, the measured permeability values tend to be overestimated. To enhance the computational accuracy of nuclear magnetic resonance permeability, it is necessary to conduct an in-depth analysis of the causes of overestimation and establish corresponding correction methods. This paper systematically conducted NMR transverse relaxation time (T₂) spectroscopy experiments under different saturation states, including water-saturated, bound water, oil-saturated, and residual oil conditions. By comparing the T₂ spectra of the same core sample in water-saturated and oil-containing states, it was found that light crude oil causes a significant rightward shift in the distribution of macropores within the T₂ spectrum, while the distribution of micropores remains largely unchanged. This indicates that light oil is the primary cause of T₂ spectrum anomalies and NMR permeability deviations. Based on this, T₂ cutoff values for different reservoir types were determined through core classification, and a T₂ spectrum correction method calibrated for macropore components was established. Results demonstrate that this method can effectively correct T₂ spectra from light oil-bearing reservoirs to fully water-saturated conditions, significantly enhancing the accuracy of NMR permeability measurements. 

Key words: Nuclear magnetic resonance (NMR), T2 spectrum correction, permeability, low permeability sandstone, ?light crude oil?