3 years ago

Crude Oil Adsorbates on Calcite and Quartz Surfaces Investigated by NMR Spectroscopy

Crude Oil Adsorbates on Calcite and Quartz Surfaces Investigated by NMR Spectroscopy
John G. Seland, Henrik N. Sørgård, Christian Totland, Willy Nerdal
The complexity of crude oils may contribute to alteration of petroleum reservoir wetting states in ways that cannot be mimicked by model oils. Subsequent to a wet aging procedure, the molecular arrangements of crude oil adsorbates and water on calcite and quartz surfaces were investigated by various 1H NMR techniques. Solid state magic angle spinning (MAS) magnitude mode, 1H–1H double-quantum single-quantum (DQSQ), and 1H single pulse NMR spectra were used to directly observe molecules on both surfaces. T1 and T2 relaxation time measurements were used to determine molecular surface arrangement. Liquid state 1H NMR was used to investigate possible differences in the crude oil caused by the aging procedure. 1H DQSQ spectra were found most valuable in assignment of the quartz surface where the resonances from the entire adsorbate were relatively well resolved. In addition to adsorbate molecular positioning, this study also provides quantitative measurements of water present at both surfaces subsequent to wet crude oil aging. Acid adsorption was determined to be the main mechanism responsible for alteration of wetting state on both the calcite and the quartz surface. NMR experiments show that organic acids adsorb directly onto calcite through electrostatic attraction while the same acids are indirectly adsorbed onto quartz through solubilization in the water phase present at the surface. A series of 1H single pulse NMR experiments at temperatures ranging from 293 to 233 K revealed that the quartz surface possesses two different water environments while the calcite surface has only one.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b07125

DOI: 10.1021/acs.jpcc.7b07125

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