PNNL

Abstract

13C nuclear magnetic resonance (NMR) spectroscopy shows that high resolution spectra of isotopically enriched CH4 and CO2 can be obtained for a natural shale sample under in situ conditions relevant to petroleum reservoirs (T = 323K and Pfluid = 90 bars) 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 design of the methods used in enhanced petroleum production. The NMR results show that CH4 and CO2 readily displace each other in the nano- (10 nm) pore spaces of the shales; that CH4 in nanopores, mesopores, and bulk fluid can be distinguished; and that the partitioning of CH4 between nanopores and mesopores depends on the CH4/CO2 ratio and, thus, partial pressures of the individual fluid species.