Drying of a porous rock monitored by NMR imaging

Abstract

The drying of a limestone block was studied by analysing one-dimensional projections (profiles) and three-dimensional (3D) NMR images as well as free induction decay (FID), as a function of the amount of water remaining in the sample at various stages of the drying process. From these results, the water repartition in the sample stays continuous and fairly uniform down to a water content W of the order of 2% in weight of water per weight of rock. However, at the end of the drying, for W<2%, water is no longer uniformly distributed. The remaining water is concentrated in the centre of the block where the NMR signal is intense, whereas in the surrounding region the NMR signal is drastically weaker. This is the first report on drying of a porous stone monitored by NMR imaging through to its late stage. These first results show spatial compartmentation and modification of the physicochemical state of the protons during the drying, which would be difficult to observe with other techniques. The authors suggest a two-compartment model which is consistent with images and profiles.