Effect of aqueous electrolyte concentration and valency on contact angle on flat glass surfaces and inside capillary glass tubes

Multiphase flow in underground formations is controlled to a large extent by capillary forces that depend on the interfacial tension, contact angle and pore diameter. The interfacial tension and contact angle depend mainly on the type of brine and its concentration. In this study, the static contact angles on flat glass surfaces have been explored as a function of brine concentrations, while the static contact angles inside glass micro-tubes have been studied as a function of pore diameter and brine concentrations for monovalent (NaCl, KCl) and divalent (MgCl2, CaCl2) brine solutions. The concentrations ranged from 0.001 to 6 M under ambient conditions, depending on the investigated salt, while the inner diameters of the glass micro-tubes ranged from 100 to 1000 mu m. A linear correlation (h = 0.3249 x d - 4.6203) between the glass micro-tube inner diameter and the meniscus height was obtained for the above solutions for concentration of less than or equal to 1 m. This correlation can be used with the Cheong equation to calculate the contact angle of the investigated solutions when only the micro-tube pore diameter is known. The results also showed that salt concentration and valency have more influence on contact angles on flat glass substrates than inside micro-sized glass tubes. In general, the contact angles on a flat glass surface increased with increasing concentration. On the other hand, the contact angles inside glass micro-tubes showed no variation with increasing concentration but increased slightly as the capillary inner diameters decreased. The difference might be associated with the curvature of the three-phase contact line. The contact angles on flat glass surfaces (approximate to 63-90 degrees) were much higher than those inside the glass capillaries (approximate to 24-33 degrees).