(626d) Atomic Force Microscopy of Hydrolysed Polyacrylamide Adsorption Onto Calcium Carbonate

Carbonate reservoir rock strengthening via chemical methods is essential to avoid carbonate fines migration during hydrocarbon extraction. In this work, we study the interaction of hydrolysed polyacrylamide (HPAM) of two molecular weights (F3330, 11 – 13 MDa; F3530, 15 – 17 MDa) with Iceland Spar calcite crystal via atomic force microscopy (AFM). Here, the tip of the AFM cantilever is attached with calcium carbonate (CaCO₃) particles to ensure any interaction registered by the instrument is solely between CaCO₃ surfaces bearing adsorbed HPAM. Force mapping scan mode is selected to scan areas of interest in pixels. This scan mode acquires a full force-distance curve at each pixel enabling useful force parameters including polymer adhesion and interaction energy with substrate surface to be obtained. Force mapping results indicate that F3330 displays higher adhesion and interaction energy with CaCO₃ than F3530. This is likely due to the F3330 molecules, having lower molecular weight, assembling relatively flatter on the calcite surface, creating more anchor points with the surface in the form of train segments. These segments are, in turn, likely due to the electrostatic attraction of the charged COO^- group of the HPAM with the positively charged calcite surface. The adhesion and interaction energy of both HPAM with CaCO₃ can be decreased by increasing the salt concentration of the NaCl solvent from 0.1% to 3%. The reduction of adhesion and interaction energy is likely due to the screening of the COO^- charged group of HPAM by salt cations, leading to a reduction of electrostatic attraction between the negatively-charged HPAM with the positively-charged CaCO₃.