Determination of T2 distribution in the presence of significant internal field gradients

The internal field gradients in rocks have a significant effect on their nuclear magnetic resonance (NMR) transverse relaxation time distribution (T2), which can lead to enhanced T2 relaxation rates, resulting in inaccurate estimates of reservoir parameters such as porosity, irreducible water saturation, permeability, and uncertainty in pore fluid typing. In an attempt to remove such effects, the distribution of the internal field gradients of a water-saturated rock sample was first obtained by the (T2, G) two-dimensional NMR method, and then a software procedure was devised to remove the effect of such gradients on T2 distribution. Experimental data of water-saturated sandstone with paramagnetic impurities were processed using this method. The results show that this method can largely remove or reduce the effects of internal field gradients on T2 distribution. The limitations of this method were explored by numerical simulation. (paper)