Correlations between diffusion, internal magnetic field gradients, and transverse relaxation in porous systems containing oil and water

Abstract

The main focus in this study is to investigate the correlations between internal magnetic field gradients (G0) and transverse relaxation times in liquid-saturated packings of glass beads of different wettabilities. We show how these correlations can be expressed as two-dimensional (2D) diagrams of distribution functions between internal magnetic field gradients and T2 values. In the case where it is difficult to distinguish the signals from oil and water, we separate them based on their difference in diffusivity. In addition to using such diffusion weighting in the G0-T2 diagrams, we also show results from experiments where the direct correlation between diffusion and T2 (D-T2) is determined. The overall results show that the wettability of the glass beads has a strong influence on the appearance of these diagrams, in particular on the location of the fast diffusing water molecules. However, due to their lower diffusivity, the transverse magnetization of the oil molecules is not so greatly influenced by either the presence of the glass beads or their wettability properties. Thus, the wettability properties of a liquid-filled porous material can be determined from the location of the water signal in such 2D diagrams. In particular, we show that this is the case not only for D-T2 diagrams, but also for G0-T2 diagrams.

The dependence on magnetic field strength of correlated internal gradient relaxation time distributions in heterogeneous materials

“…Because of their dependence on characteristics of the pore space, several techniques have been developed to take advantage of internal gradients to find pore shape [20], pore connectivity, [21] or wettability [22]. We present here a novel 2D inverse Laplace NMR technique which could assist better understanding of the distribution of internal gradients as a function of pore size.…”

Observation of molecular migration in porous media using 2D exchange spectroscopy in the inhomogeneous magnetic field

“…Being an exchange method, the technique senses changes in T 2 values as evidenced by the growth of off-diagonal intensity following a mixing time during which molecules are allowed to diffuse. This method relies on the use of two-dimensional Laplace inversion [5] and is one of a number of 2D separation, correlation and exchange methods [6,3,[7][8][9][10][11] based on this type of analysis. However, there are difficulties associated with the inverse Laplace Transform because of pearling effects [12].…”

Relationship between susceptibility induced field inhomogeneities, restricted diffusion, and relaxation in sedimentary rocks

“…This is consistent with the results presented here. Seland et al [19] studied the correlation between internal gradients and transverse relaxation in samples of packed glass beads of different wettabilities and different saturation states.…”