Determination of pore structures and dynamics of fluids in hydrated cements and natural shales by various ¹H and ¹²⁹Xe NMR methods

Highlights

• Porous structure of shales and cements was studied by ¹H and ¹²⁹Xe NMR spectroscopy.

• Xenon highlights capillary pores in cements and micropores in shales.

• NMR cryoporometry reflects mesopore size distribution in shales.

• Chemical composition of shales affects the paramagnetic effects.

Abstract

Cements and shales play a vital role in the construction and energy sectors. Here, we use a set of advanced NMR methods to characterize the porous networks and dynamics of fluids in hydrated cement and shale samples. We compare the properties of cements from two different manufacturers, BASF and Portland, as well as shales brought from USA and China. ¹²⁹Xe NMR spectra of xenon gas adsorbed in the samples indicate that the capillary mesopores are smaller and the exchange between free and confined gas is slower in the Portland than in the BASF cement samples. The pores probed by xenon in the shale samples from USA are significantly smaller than in the cement samples, partially in the micropore region. There is a substantial difference in between the ¹²⁹Xe spectra of shales from USA and China. Whereas the latter show a clear signature of paramagnetic impurities by exhibiting large negative ¹²⁹Xe chemical shifts (referenced to the free gas), the samples from USA lack the negative chemical shifts but feature large positive shift values, which may indicate the presence of micropores and/or paramagnetic defects. ¹H NMR cryoporometry measurements using acetonitrile as probe liquid allowed the observation of mesopores in the shale samples as well, and T₂-T₂ relaxation exchange experiment enabled the quantification of the exchange rates between free and confined acetonitrile.