NMR SIGNALS OF UNSATURATED CLAY SEDIMENTS

The existence of clay affects the simulation of conductivity and permeability in reservoir rocks because of clay-water interaction mechanisms of capillarity and adsorption. Thus, quantification of water content and states in clays are of great importance for evaluating the contribution of clay to reservoir rocks. Nuclear magnetic resonance (NMR) offers the opportunity to detect the information about the clay-bound water in a noninvasive way. To better understand the mechanism of the water in clay contributed to the flow properties of reservoir rocks, we design an experiment of pure clay by varying with the water content using NMR. Cylindrical soil samples of kaolinite, illite, calcium-based montmorillonite, and sodium-based montmorillonite were prepared in equilibrium under various saturated salt solutions with different degrees of saturation of water. The NMR relaxation time T₂, T₁-T₂, and D-T₂ are measured for each sample. In this presentation, we will report how the NMR signals change as the water content decreases for these four clay sediments. The minimum T₂ value (or T₂-cutoff), as the characteristic T₂ value corresponds to boundary of the bound and free water in porous materials, can be further investigated to differentiate between adsorptive water and capillary water in different clays. The self-diffusion coefficient of water, captured in D-T₂ mapping, is also modified to reflect retention regimes of the pore water at varying water contents. Our results provide new insights into water status in clay sediments and aid broadly in evaluating oil/gas production.