Carbonate rock wettability changes induced by organic compound adsorption

The knowledge and understanding of carbonate rocks wettability are important factors in predicting oil extraction and evaluating oil pool profitability. We have studied benzoic acid adsorption onto a calcium carbonate powder to determine the influence of organic acid compound adsorption on the mineral behaviour. The compound was dissolved in an organic phase containing different amounts of water and the covering was evaluated thanks to thermogravimetry. It enabled us to draw adsorption isotherms and to notice a greater adsorption with an increasing water concentration. We also noticed that the isotherm reached two plateaus and presented a rapid increase for equilibrium concentration higher than 1 g/l. We discussed a possible adsorption process with the help of Insight II molecular modelling software and contact angle measurements. It seems that benzoic acid molecules recombine in a more crystallized state to form a monolayer at the second plateau. For higher concentrations, there is precipitation of a new compound that may be calcium dibenzoate. Contact angle measurements on compacted pellets show a less hydrophilic surface induced by benzoic acid adsorption. (C) 1998 Published by Elsevier Science B.V. All rights reserved.