Quantitative Study on Surface Bound Water of Clay with Low Field NMR

The types and extents of clay hydration are directly related to the stabilization of water sensitive shale borehole. Thermogravimetric analysis, a widely used method presently in determining the type and content of clay in formation rocks, is unable to quickly, intuitively and quantitatively measure the type and extent of clay hydration. Based on the relationship between low field NMR T₂ relaxation spectrum and the mobility of water molecules, the total signal amplitude of the T₂ peak is used to determine the total water content in clay, the ranges of T₂ values to determine the types of clay hydration, and the area of the T₂ peak to determine the contents of three kinds of water. Laboratory experiments showed that the strongly bound water, weakly bound water and free water in water-saturated clay have T₂ values ranging in 0.001-0.1 ms, 0.1-15 ms and 15-200 ms, respectively, corresponding to the contents of the three kinds of water, which are 14.83%, 67.69% and 17.48%, respectively. The T2 relaxation spectrum also intuitively demonstrates that temperature buildup drives water molecules in clay from low degree of freedom to high degree of freedom. BPEI with 8 amino groups is able to dispel more than 90% of the strongly and weakly bound water and all the free water from clay.