A rapid measurement of T1/T2: the DECPMG sequence

The Driven-Equilibrium Carr-Purcell Meiboom-Gill (DECPMG) pulse sequence is a rapid method for obtaining the average ratio of longitudinal to transverse relaxation times (T(1)/T(2)) as a function of T(2). Since this is a one-dimensional experiment, the (T(1)/T(2))T(2) ratio can be acquired, potentially, in just two scans; the second scan being a reference CPMG measurement. Conventionally, T(1)/T(2) is determined from a two-dimensional T(1)-T(2) relaxation correlation experiment. The method described here offers a significant reduction in experimental time without a reduction in signal-to-noise. The (T(1)/T(2)) ratio is useful for comparing the behaviour of liquids in porous media. Here we demonstrate the application of the DECPMG sequence to the study of oil-bearing rocks by differentiating oil or water saturated rock cores, and by observing the relative strengths of surface interaction for water in two types of rock by measuring (T(1)/T(2)) as a function of magnetic field strength.