Swelling of Kimmeridge kerogen by normal-alkanes, naphthenes and aromatics

Despite recognition of kerogen swelling in liquid solvents, swelling trends in different classes of petroleum liquids remain unexplored. Modeling results based on the extended polymer theory have not been beyond curve-fitting of swelling measurements. This work centers on measurement of swelling of Kimmeridge kerogen in three classes of petroleum liquids: normal-alkanes, naphthenes and aromatics. The measured data show that swelling decreases as the molecular size increases for the three classes of solvents. Compared with naphthenes, normal-alkanes with flexible linear chains, and aromatics having pi-pi interaction with kerogen induce higher swelling. In the Kimmeridge kerogen, the swelling in both normal-alkanes and naphthenes monotonously decreases with the solvent solubility parameter and molar volume starting with hydrocarbon molecules with 5 carbon atoms. Compared with solvent solubility parameter, the effect of solvent molar volume dominates the swelling of Kimmeridge kerogen. The extended Flory-Rehner and regular solution theory framework does not describe the swelling behavior of Kimmeridge kerogen in petroleum liquids despite widespread applications of the framework. Results from the model show an increase in swelling in normal alkanes with molecular size which is opposite to our measurements.