Comparison of adsorption ability of PAM, APAM and CPAM on Sodium-Montmorllonite surface: A molecular dynamics study

Abstract

Swelling of clay minerals caused by the adsorption of water is one of the main problems encountered in oil well drilling industry during the operations of drilling with water-based fluids. Different types of chemicals can be used as inhibitor to solve the hydration of clay minerals in drilling fluids operations. So, the adsorption process of novel polymer inhibitor remained as well a complex surface phenomenon to understand. Recently, the polymer adhesion mechanism and the development of novel polymer inhibitors that can impart improved adhesion characteristics have become ultimately important to the drilling process. In this research, molecular dynamics simulations are applied to quantify and compare the adsorption density of PAM (Nonionic Polyacrylamide), APAM (Anionic Polyacrylamide) and CPAM (Cationic Polyacrylamide) on Sodium Montmorllonite (Na-MMT) Surface. And also to analyze the hydration inhibition effectiveness for solving shale swelling problem while drilling well. This work mainly explained and summarized the parameters which achieve directly the adsorption mechanism and affect the inhibition process. Including the adsorption characteristics of PAM, APAM and CPAM. The simulation results show that PAM and APAM molecules have low adsorption density on Na-MMT surface compared to CPAM molecules. PAM and APAM molecules interact more through h-bonding with their own molecules leading to a weak interaction with Na-MMT particles. CPAM molecules provide high mobility and have good attraction with Na-MMT particles through electrostatic forces, Van der Waals forces and hydrogen bonding. APAM exhibit high energy, as the distance between its molecules and MMT increase, due to high electrostatic repulsion caused by the negative charge. The adhesion of CPAM molecules affects the inhibition of Na-MMT surface hydration more than PAM and APAM.