Global characterization of kerogen from three argillaceous formations : oligocene (Mol, Belgium), Callovo-Oxfordian (Bure, France), and Toarcian (Tournemire, France)
Congress title :Bridging Clays 4ème Colloque du Groupe Français des Argiles et 43ème Réunion de la Clay Minerals Society américaine
Congress town :Ile d'Oléron
Congress date :05/06/2006
Deep argillaceous formations are potential long-term nuclear waste repositories because of their low permeabilities and high sorption capacities with respect to radioelements and heavy metals. Three argillaceous formations are considered in this study: a plastic one (Oligocene) selected in Belgium (Mol) containing 3 % w/w of organic matter and two consolidated ones (Callovo-oxfordian and Toarcian) selected in France (Bure and Tournemire respectively) containing around 1 % w/w of organic matter. For the three rocks, organic matter is mostly insoluble (kerogen). Upon temperature elevation related to a high-activity waste disposal, kerogen may release significant quantities of gaseous and liquid effluents. The latter may affect the efficiency of the geological barrier through modification of the physico-chemical parameters (e.g. pH, ionic strength, pressure). Previous studies [1, 2] performed on Mol rock have shown the capacity of its kerogen to release O-containing compounds even at unusually low temperatures. Their complexation properties may thus play a major role in the retention or migration of the radionucleides.
A parallel study is carried out on Bure and Tournemire kerogens to compare their behaviour with that of Mol. This comparison is based on spectroscopic features (FTIR, solid state 13C NMR) and pyrolytic results (Rock-Eval, Curie point pyrolysis coupled with gas chromatography and mass spectrometry). The global characterizations of Bure and Tournemire kerogens are very closed and show significant differencies with the Mol one. If all kerogens are a mixture of type II/III, their maturity increases from Mol to Bure and Tournemire. Lower yields of effluents are observed upon pyrolysis of Bure and Tournemire kerogens when compared to Mol case, in agreement with their higher maturity. In addition, kerogen from the two French formations exhibits lower oxygen content than the Belgian one, as well as the released effluents. However, an early production of CO2 is observed in the three cases, which may induce a rapid substantial decrease in pH of the groundwaters and mineral dissolutions.