Interaction of Hydrocarbons with Clays under Reservoir Conditions: In Situ Infrared and Nuclear Magnetic Resonance Spectroscopy and X-ray Diffraction for Expandable Clays with Variably Wet Supercritical Methane

Abstract

The results from novel in situ high-pressure nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, and X-ray diffraction (XRD) investigation of the interaction of the smectite hectorite with variably wet supercritical methane (scCH4) at 90 bar and 323 K (hydrostatic conditions equivalent to ∼1 km depth) show that CH4 occurs in the clay interlayers, in pores external to the individual clay particles, and as bulk fluid. The occupancy of each environment depends on the relative humidity (RH) of the CH4-rich fluid and the hydration energy and size of the charge-balancing cation. As RH increases, the fraction of interlayer and interparticle CH4 decreases, although with Cs+, addition of a small amount of H2O initially increases CH4 uptake. Maximum interlayer CH4 adsorption occurs when the mean basal spacing just permits methane intercalation (∼11.5 Å) and never below this basal spacing. It is also higher with divalent cations than with monovalent cations. The data show that CH4 adsorption occurs predominantly via a weak dispersion interaction with the clay and that its intercalation occurs via a passive space-filling hydrophobic mechanism. The results suggest that, under reservoir conditions, smectite interlayers may provide a reservoir for CH4 under low-water conditions.

Understanding methane/carbon dioxide partitioning in clay nano- and meso-pores with constant reservoir composition molecular dynamics modeling

“…This conclusion is consistent with the incorporation of CH 4 into the interlayer galleries of expandable clays occurring by a passive, space filling mechanism with basal spacings similar to 7.5 Å. 39 Increasing CO 2 and CH 4 incorporation with increasing pore thickness also greatly effects the coordination of the Na + ions to the pore surfaces ( Fig. 3).…”

“…These results are in good agreement with recent experimental and simulation studies that show that the basal spacing required for CO 2 intercalation in the interlayer galleries of smectite clays is less than for CH 4 due to steric effects. 6,31,32,38,39 At a pore thicknesses of 7.5 Å some CH 4 enters the pore, and the CO 2 /CH 4 ratio decreases rapidly with increasing pore thickness up to 33.0 Å ( Fig. 2a).…”

“…The results are in good agreement with previous experimental and computational, high T and P studies that show that there can be an energetic driving force for CO 2 incorporation in the interlayer galleries of expandable clay minerals, whereas CH 4 enters these spaces by a passive, space filling mechanism. 6,31,32,38,39,49 The thickness of the surface layer in which the fluid is structured (B15 Å) is similar to that in which H 2 O is structured on oxide and hydroxide surfaces, 72,73 suggesting that computational modeling of geochemically relevant fluids in nano-and mesopores bounded by such materials need only include pores with thicknesses less than a few nm to capture the essential features of their behavior. The results parallel the preference of other inorganic shale components (e.g., calcite and quartz) for CO 2 relative to CH 4 , suggesting that for oxide and oxysalt materials, CH 4 adsorption is relatively weak and its filling of pores bounded by them occurs by a passive, space filling mechanism.…”

Tuning the Hydrophobicity of Layer-Structure Silicates To Promote Adsorption of Nonaqueous Fluids: Effects of F– for OH– Substitution on CO2 Partitioning into Smectite Interlayers

“…Computational studies have shown that reducing the structural charge on the clay enhances CO2 intercalation, 37 and this may also contribute to intercalation of other hydrophobic species. As illustrated by recent experimental studies, the composition of the external fluid phase strongly affects the intercalation, with high H2O activities suppressing CO2 intercalation 21,[28][29][30][31]43 and presumably that of other hydrophobic species. It also seems likely that even with Fsubstitution, small linear and planar molecules should be more easily incorporated than large ones with complex molecular structures.…”

“…The model with 53% Fsubstitution has a composition similar to the natural San Bernardino hectorite (Clay Mineral Society SHCa-1) used in many spectroscopic studies by our group and others, which has 55% Fsubstitution. 21,42,43 Individual Fions occur in two different structural environments in the simulation models: (i) coordinated to 3 Mg octahedra and (ii) coordinated to 2 Mg and 1 Li octahedra. The ratio of these two sites used in the simulations is 60:40 in accordance with experimental 19 F NMR results for the natural San Bernardino sample.…”