The modified stretched-exponential model for characterization of NMR relaxation in porous media

A compact model, the modified stretched exponential (MSE), for characterization of transverse and longitudinal NMR relaxation of fluid in saturated porous media is presented. The MSE model exhibits the theoretically correct long- and short-time behavior, and its general applicability for representing transverse-relaxation data is demonstrated for a wide range of rock lithologies and saturating fluids at various magnetic field strengths and echo times. The model also provides a reliable and sample-independent method for signal back-extrapolation, which is necessary for quantitative petrophysical NMR measurements, and overcomes the limitations of the well-known stretched-exponential model. (C) 1996 Academic Press, Inc