Adsorption of organic acids in oil on crushed marble at varying temperatures and ambient pressure

Adsorption of organic constituents of reservoir fluids onto the surface of grains constituting carbonate reservoirs is believed to determine reservoir wettability and, at the pore scale, the flow of fluids in them. In this study, the effect of grain surface modification, duration of exposure, and temperature on stearic acid and cyclohexanepentanoic acid adsorption and their adsorption strengths on crushed marble, our model for carbonate reservoir rock, is investigated. The amount of stearic acid or cyclohexanepentanoic acid adsorbed onto the marble grains was determined using Gas Chromatography-Flame Ionization Detector (GC-FID). To characterize marble grains, Particle Size Analysis (PSA), Nitrogen Adsorption–desorption analysis (NAD), Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) were performed. Adsorption of stearic acid and cyclohexanepentanoic acid reached equilibrium after 336 h and altered the contact angle of the marble from water-wet to oil-wet. The amount of adsorption for both acids on marble increased with temperature. Adsorption results indicated that adsorption mechanisms are a combination of physical and chemical adsorption for both acids on marble grains. The adsorption strength experiments also showed that stearic acid adsorption on the marble is stronger than cyclohexanepentanoic acid adsorption. The results suggest that understanding the impact of temperature on adsorption and adsorption strength of polar components in the oil phase on rock surface is essential in carbonate reservoirs to reduce remaining oil saturation.