C-13 Nuclear Magnetic Resonance Spectroscopy of Methane and Carbon Dioxide in a Natural Shale

C-13 nuclear magnetic resonance (NMR) spectroscopy shows that high-resolution spectra of isotopically enriched CH4 and CO2 can be obtained for a millimeter-sized natural shale sample under in situ conditions relevant to petroleum reservoirs (T = 323 K, and P-fluid = 90 bar) using magic angle spinning. These results show for the first time that this technique has the potential to provide otherwise unobtainable, species-specific structural and dynamical insight into the pore systems of shales and other tight reservoir and source rocks and can thus help guide the design of the methods used in enhanced petroleum production. The NMR results show that CH4 and CO2 readily displace each other in the nanoporosity (<10 nm) and mesoporosity (>10 nm) pore spaces of the shale studied here, that CH4 in nanopores, mesopores, and bulk fluid can be distinguished by NMR, and that the partitioning of CH4 between nano- and mesopores depends upon the CH4/CO2 ratio and, thus, partial pressures of the individual fluid species.