ADSORPTION OF ORGANIC-COMPOUNDS ON CARBONATE MINERALS .1. MODEL COMPOUNDS AND THEIR INFLUENCE ON MINERAL WETTABILITY

This is the first of a series of papers to investigate the role of organic compounds on wettability, porosity and permeability of carbonate rocks. These are important characteristics that influence the performance of petroleum reservoirs. This first paper investigates the adsorption of model organic compounds to determine what type of compounds adsorb, the nature and strength of the adsorption, and the influence of adsorption on rock wettability. A wide variety of model organic compounds were tested for adsorption on calcite, dolomite and magnesite. They were adsorbed from both organic and aqueous solvents. The adsorption was monitored by thermogravimetric analysis and by contact angle wettability tests. The compounds included carboxylic acids, alcohols, sulfates, sulfonates, amines, amino acids and carboxylated polymers. Carboxylic acids adsorb most strongly, and their adsorption is stabilized by long, straight chains and by polymeric structures. Fatty acids form a surface monolayer, and carboxylated polymers also appear to coat the surface completely. These adsorbates could be desorbed only by a solvent that provided both good solubility for the adsorbate and an ionic species to replace it at the solid surface. They were interpreted to be chemisorbed as ionic species. Several other compounds exhibited physisorption and could be easily removed by most solvents. Wettability tests were performed at 20-degrees, 50-degrees and 80-degrees-C to obtain information regarding the stability of the adsorption at elevated temperatures.