23Na and 1H NMR Relaxometry of Shale at High Magnetic Field

TL;DR

This study demonstrates high-field NMR techniques, including 23Na and 1H relaxometry, to effectively differentiate and quantify fluid phases in shale, advancing formation evaluation methods for unconventional reservoirs.

Contribution

It introduces high-field (9 T) 2D T1-T2 NMR measurements and 23Na NMR as novel tools for shale fluid typing and phase separation, surpassing current low-field methods.

Findings

High-field NMR can distinguish hydrocarbon and aqueous phases in shale.

23Na NMR effectively identifies brine content and salinity.

The methods are validated on various porous materials, including Eagle Ford shale.

Abstract

Formation evaluation of unconventional reservoirs is challenging due to the coexistence of different phases such as kerogen, bitumen, movable and bound light hydrocarbon and water. Current low-frequency (0.05 T) nuclear magnetic resonance (NMR) laboratory and logging methods are incapable of quantitatively separating the different phases. We demonstrate the utility of high-field (9 T) NMR 2D T1-T2 measurements for separating hydrocarbon and the clay-interacting aqueous phases in shale based on the difference in the frequency dependence of the spin-lattice relaxation time. Furthermore, we demonstrate 23Na NMR as a promising complementary technique to conventional 1H NMR for shale fluid typing, taking advantage of the fact that sodium ions are only present in the aqueous phase. We validate high-field (9 T) 23Na-1H NMR relaxometry for assessing brine-filled porosity and brine salinity in various porous materials, including porous glass, conventional rocks, clays, and shale, and apply it for differentiating hydrocarbon versus aqueous components and also the clay-associated versus free water in Eagle Ford shale cores. This work lays the groundwork for developing future downhole 23Na-1H NMR logging techniques.