(225j) Polyacrylamide Adsorption Onto Calcite Surface Predicted By Molecular Dynamic and Monte Carlo Simulation

The polymer flooding in petroleum reservoirs is one of the main techniques used for enhanced oil recovery. However, the retention of polymers on the surface of rock pores has been one of the major problems that affect the efficiency of the process and cause a reduction in the formation permeability, especially in carbonate reservoirs. Adsorption is one of the main mechanisms of polymer retention, but until today, there are no techniques to discriminate adsorption from other mechanisms. Molecular simulation techniques can be used to isolate the contribution of adsorption, examine details of the mechanism and predict the amount adsorbed. The present study used a new combination of molecular dynamics and Monte Carlo techniques to evaluate the adsorption of polyacrylamide on calcite. Two models of polyacrylamide molecules were elaborated, with 30 and 50 monomers. To enable the adsorption study, which is complicated by the high dilution of polymer solutions, we combine molecular dynamics and Monte Carlo techniques. The behavior of these molecules in the aqueous phase was determined through molecular dynamics simulations, obtaining stable conformations of the polymer in water. With the stabilized polyacrylamide structures obtained, we performed Monte Carlo simulations to study the adsorption of polyacrylamide on calcite surface. Values of maximum adsorbed amount and molecular conformations with different polymeric chain sizes and at different concentrations showed good agreement with experimental results obtained from the literature. Details of the adsorption mechanism were also evidenced.