High field solid-state nuclear magnetic resonance experimental study for clay and shale swelling, A

Abstract

The development of the shale resources faces many problems related to their complex structure and challenging conditions. Drilling and fracturing operations suffer from the swelling tendency of clays and shale formations. The expansion mechanisms of clays have been discussed in detail in the literature and several theories have been developed to predict the swelling in shales. The crystalline (interlayer), double-layer, and the layers breakage/formation swelling mechanisms are the mechanisms that are the most contributing for the clay swelling. They all depend on the ionic concentration of the system. Low frequency NMR technique has been used in the industry mainly to determine the rock properties. NMR has also been used to determine the chemistry of the matters, especially in high frequency fields in chemistry and other scientific applications. Yet, to the author's knowledge, there has been no high field NMR study exists to describe the swelling behavior of the clays. In this study, we conducted an experimental investigation to determine the feasibility of high frequency NMR measurements in characterizing the expansive behavior of pure clays and shale formations. Mainly, the benefits of utilizing the high field NMR for studying the swelling behavior of clays have been investigated and NMR data was collected and analyzed (e.g. relaxation times and distributions) for various liquid/clay systems. NMR data was also correlated to petrophysical and acoustic properties of pure clays and shales reported in the literature. An ultimate goal of this work is to evaluate the feasibility of the high field NMR use for characterization of the unconventional resource shale systems, in particular the Eagle Ford shale. In this study, high field NMR has been used to determine several clay and Eagle Ford shale structure and to measure the relaxation times of dry and saturated samples. Moreover, the relaxation time distribution curves have been used to identify the dominant swelling mechanism(s) taking place in the pure clays studied. Our study concentrates on the pure montmorillonite as it has the highest affinity to liquids. Few kaolinite and Eagle Ford shale samples have also been investigated to compare to the montmorillonite results and to present NMR data utilization in unconventional resource characterization.