Improved Description of Organic Matter in Shales by Enhanced Solid Fraction Detection with Low-Field ¹H NMR Relaxometry

Abstract

Nuclear magnetic resonance (NMR) relaxometry is routinely used to characterize the oil fraction in unconventional shale formations with low-field benchtop NMR hardware. However, organic phases with restricted mobility like kerogen and bitumen are typically not detectable with the standard Carr− Purcell−Meiboom−Gill (CPMG) method on such equipment, with the rapid spin−spin (T 2 ) signal decay of these solid/viscous components not visible to the measurement. The solid-echo (SE) and mixed-echo (ME) pulse sequences offer an alternative to the CPMG, extending the lifetime of the time-domain signal and allowing the capture of solid hydrogen-containing species. Accordingly, we combine NMR relaxation data generated from the application of the CPMG, SE, and ME experiments to a set of powdered oil-and brine-saturated Eagle Ford shale samples, with the aim of identifying and quantifing both the immobile (kerogen/bitumen) and mobile (oil/brine) components. Two-dimensional relaxometry correlating spin−lattice relation times T 1 to the effective decay times T 2 obtained using CPMG and SE techniques provides more complete information on the immobile phases in the shales, such as solid organic matter and clay-bound water. The three spin−echo techniques have similar efficiencies when detecting signal from mobile and low-viscosity fluids, while significant differences are seen in shale samples containing immobile organics. Overall, the combination of the three spin echo techniques provides an improved description of the solid, viscous, and liquid components in the investigated shales at low magnetic field.

2021 Pioneers in Energy Research: Alan Marshall

“…The historical perspective and recent progress on the integration with mass spectrometry within the past decade were reviewed. Panattoni, Magusin, and co-workers reported the use of nuclear magnetic resonance (NMR) relaxometry to characterize the oil fraction in unconventional shale formation and demonstrated that the combination of spin–echo techniques can provide an improved description of organic matter in shales at a low magnetic field . The recent addition of the non-contact atomic force microscopy (nc-AFM) technique into the characterization toolbox was demonstrated by an original article by Chen, Yao, Zhang, and co-workers, who demonstrated the complementary use of nc-AFM and FT-ICR MS to provide mechanistic insights into molecular growth during carbonization …”

Correlating Surface Chemistry to Surface Relaxivity via TD-NMR Studies of Polymer Particle Suspensions

“…Substantial work has been done comprising TD-NMR studies of porous media, including particle suspensions, − catalysis, − zeolites ,, construction products, , and bioengineering. − Additionally, in the petroleum field, NMR logging allows the evaluation of the porosity and permeability of reservoir rocks and shales upon calibration via laboratory measurements. − The impact of surface chemistry on solvent relaxation measurements has been acknowledged in several studies. For instance, Schlumberger et al showed that Stöber silicas may have a wetting preference for water compared to ethanol and tetrahydrofuran using T 1 and T 2 measurements .…”