CommunicationDetection of intermolecular homonuclear dipolar coupling in organic rich shale by transverse relaxation exchange

•Intermolecular dipolar coupling detected between liquid and organic solids in shale.•T2-T2 exchange pulse sequence used to observe magnetization exchange.•Extensive exchange seen between the liquid hydrocarbon and organic matter.•Diffusive coupling also seen between organic and inorganic porosity.

The mechanism behind surface relaxivity within organic porosity in shales has been an unanswered question. Here, we present results that confirm the existence of intermolecular homonuclear dipolar coupling between solid and liquid phases in sedimentary organic matter. Transverse magnetization exchange measurements were performed on an organic-rich shale saturated with liquid hydrocarbon. Liquid and solid constituents were identified through both sample resaturation and through their T1/T2 ratios. Extensive cross peaks are observed in the T2-T2 exchange spectra between the solid and liquid constituents, indicating an exchange of magnetization between the two phases. This result cannot arise from physical molecular diffusion, and the dissolution energies are too high for chemical exchange, such that the magnetization exchange must arise from intermolecular homonuclear dipolar coupling. These results both confirm a possible source of surface relaxivity in organic matter and emphasize caution in the use of standard porous media interpretations of relaxation results in shales because of coupling between different magnetization environments.

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