Effect of oilfield chemicals on the cloud point of nonionic surfactants

An experimental study was conducted to assess the effect of various oilfield chemicals on the cloud point of nonionic surfactants of the Triton-X series. The effects of simple salts, alkalis, acids, polymers, scale and corrosion inhibitors, biocides, a mutual solvent and a crude oil on the cloud point of several nonionic surfactants were examined over a wide range of parameters. The study also included evaluation of several additives, including short-chain alcohols, urea, and anionic surfactants, to raise the cloud point of these surfactants under oil reservoir conditions. The results obtained in this study indicated that oilfield chemicals affect the cloud point of nonionic surfactants, and the effect depends on the number of ethylene oxide groups, n, of the surfactant. At acid concentrations greater than 1 wt.%, hydrochloric or acetic acid increased the cloud point of nonionic surfactants having n>7, with a higher cloud point being obtained with hydrochloric acid. Alkalis caused a sharp drop in the cloud point of nonionic surfactants. This effect was enhanced in the presence of sodium chloride. Anionic and cationic polymers depressed the cloud point of nonionic surfactants. Addition of an anionic polymer to alkaline solutions of TX-100 resulted in a further drop in the cloud point. Addition of urea or methanol increased the cloud point of nonionic surfactants having n>7. Sodium dodecyl sulfate (SDS) raised the cloud point of neutral and alkaline solutions of TX-100 at low sodium chloride concentrations only. SDS also raised the cloud point of TX-45 (n=5) at SDS concentrations greater than 0.8 wt.%. The effect of mutual solvent on the cloud point of the four nonionic surfactants depended on the concentration of the mutual solvent and the number of ethylene groups in the surfactant. (C) 1997 Elsevier Science B.V.