Estimation of thermodynamic properties for kerogen present in Boom Clay

In Belgium, Boom Clay (BC) represents one of the potential host rocks considered for the disposal of high-level and/or long-lived radioactive waste. The latter corresponds to heat generating waste which during disposal and the thermal phase may affect the rock properties and porewater chemistry. In this respect, it has been shown by different authors that perturbations, such as oxidation and/or thermal stress may lead to the degradation of the organic matter, i.e. kerogen comprised in BC. Although many studies on the solid and also on the dissolved OM pools of Boom Clay have been performed in the past, a thermodynamic description of the Boom Clay kerogen (BCK) and its degradation (products) is still lacking. BCK subjected to oxidation or thermal stress may generate thermolabile components and lead to the release of oxygen-containing polar products, like carboxylic acids and phenols which may affect the transport behavior of some radionuclides and chemotoxic elements due to complexation. In addition to water-soluble compounds also CO₂ is formed by the thermal cracking of kerogen. Based on spectroscopic methods and pyrolysis experiments previously performed on isolated BCK, the organic compounds constituting its macromolecular structure (i.e. n-alkanes, branched alkanes, aromatic hydrocarbons and oxygen compounds) were identified. The latter and application of the so-called group contribution approach allowed to estimate the thermodynamic standard state properties of BCK at 25 °C and 1 bar. The derived thermodynamic properties enable to formalize the geochemical reactions described above, as well as calculation of stability relations for different kerogen compositions under physicochemical conditions of the BC formation.