Molecular dynamics simulations to study the adsorption damage of modified polyacrylamide in sandstone pores

In fracturing stimulation, the adsorption of thickening agent molecules will cause reservoir damage, which will affect the fracturing stimulation performance. Therefore, it is very important to study the influencing factors of the adsorption of polymer molecules on the rock surface to reduce the polymer adsorption damage. In this paper, we simulated the adsorption behavior of modified polyacrylamide on the quartz surface to investigate the polymer adsorption on the sandstone. The shear properties of polyacrylamide (PAM) solution were studied using molecular dynamics. The adsorption energy, mean square displacement, radial distribution function, etc. were calculated in this work. Then, the adsorption behavior of PAM molecules on the quartz surface was analyzed. The adsorption of PAM on the quartz surface is mainly through the hydrogen bonding force formed between amide groups of PAM and hydroxyl groups of the quartz surface. Hydrogen bonds are easily broken at high temperatures. Therefore, the adsorption stability of PAM molecules will reduce with the increase in temperature. Moreover, the influence of modified monomers AA and AMPS on the adsorption stability, adsorption mechanism, and viscosity of the PAM solution under different conditions was studied. The shear simulation showed that modified monomers of AA and AMPS had a certain enhancement action on the viscosity of the PAM solution. However, stability studies revealed that adsorption damage will also increase accordingly. The research results provided some theoretical references for the development of low-damage fracturing fluid for ultra-low permeability reservoirs in the future.