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Molecular dynamics simulation of brine droplet wetting on sandstone surface
LIU Bing1, YANG Jie1, ZHAO Li2, ZHANG Jun1, SHEN Yue1, LI Zhen1, WANG Yu-dou1
(1.College of Science in China University of Petroleum, Qingdao 266580, China;2.Research Institute of Oil Production Technology, Shengli Oilfield Company Limited, SINOPEC, Dongying 257061, China)
Abstract:
Molecular dynamics (MD) simulation was performed to investigate the microscopic wetting behavior of water droplets on the sandstone in the presence of NaCl. The simulation results show that NaCl can transform the hydrophilic SiO2surface into weak hydrophilicity. The wettability of water droplet on SiO2surface is weakened with brine concentration increasing. The contact angle increases with the increase of the NaCl concentration until the density rises to 19.6%. The potential of mean force (PMF) between water molecules and Na+ or Cl- indicates that the binding energy barrier is higher than dissociation energy barrier, which causes water molecules gathering around Na+ or Cl-, and therefore leading to the increase of contact angle. The adsorption energy between the sandstone surface and the water molecules decreases with the increase of the NaCl concentration. However, when the concentration is beyond 19.6%, the adsorption energy changes little, which is consistent with the trend of the change in contact angle.
Key words:  brine  sandstonesurface  wettability  molecular dynamics simulation  adsorption energy