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Realistic molecular model of kerogen’s nanostructure

Abstract

Despite kerogen’s importance as the organic backbone for hydrocarbon production from source rocks such as gas shale, the interplay between kerogen’s chemistry, morphology and mechanics remains unexplored. As the environmental impact of shale gas rises, identifying functional relations between its geochemical, transport, elastic and fracture properties from realistic molecular models of kerogens becomes all the more important. Here, by using a hybrid experimental–simulation method, we propose a panel of realistic molecular models of mature and immature kerogens that provide a detailed picture of kerogen’s nanostructure without considering the presence of clays and other minerals in shales. We probe the models’ strengths and limitations, and show that they predict essential features amenable to experimental validation, including pore distribution, vibrational density of states and stiffness. We also show that kerogen’s maturation, which manifests itself as an increase in the sp2/sp3 hybridization ratio, entails a crossover from plastic-to-brittle rupture mechanisms.

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Figure 1: Kerogen in organic-rich shale formations.
Figure 2: Reconstruction of molecular models of kerogens.
Figure 3: Experimental validation of the molecular models.
Figure 4: Elastic properties of molecular models of kerogen.
Figure 5: Fracture testing of the four kerogens with ρ = 1.2 g cm−3.

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Acknowledgements

This work was supported by the X-Shale project enabled through MIT’s Energy Initiative, with sponsorship provided by Shell and Schlumberger. Additional support was provided by the ICoME2 Labex (ANR-11-LABX-0053) and the A MIDEX projects (ANR-11-IDEX-0001-02) co-funded by the French programme ‘Investissements d’Avenir’ managed by ANR, the French National Research Agency. The authors thank M. Hubler (MIT) and J. Gelb (Carl Zeiss X-ray Microscopy) for providing the X-Ray Microscopy image of raw shale, and A. Saul, J. M. Leyssale, H. Van Damme and A. Archereau for fruitful discussions. The neutron scattering experiments were carried out at the Spallation Neutron Source, which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy, under Contract No. DE-AC05-00OR22725 with Oak Ridge National Laboratory.

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C.B., B.C., R.J.-M.P. and F.-J.U. designed the work. C.B. performed the simulations and data treatment. A.S. and A.E.P. performed the acid demineralization with critical point drying. A.S., A.E.P., C.M.G. and C.V.-G. measured the nitrogen and CO2 adsorption isotherms. C.B. and B.C. performed the scattering measurements with G.V., G.G., M.F. and C.W. as instrument scientists. C.B., B.C., R.J.-M.P. and F.-J.U. wrote the paper.

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Correspondence to Benoit Coasne.

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Bousige, C., Ghimbeu, C., Vix-Guterl, C. et al. Realistic molecular model of kerogen’s nanostructure. Nature Mater 15, 576–582 (2016). https://doi.org/10.1038/nmat4541

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