Contact with crude oils can alter the wetting of initially water-wet surfaces.If those surfaces are flat,the effect of wetting alteration can be observed directly by changes in oiVwater contact angles.In porous media changes in wetting must be inferred from indirect measurements.The wetting conditions established either on flat surfaces or in porous media depend on the surface mineralogy,compositions of both oil and brine phases,and aging conditions(time and temperature),but as yet no clear connection between surface measurements and wetting of crude oil/brine/rock ensembles has been made.To bridge that gap,we compare the effects of a well established wetting transition that occurs with changes in aqueous phase pH on the wetting of flat surfaces and two types of cores,a synthetic silicate material and Berea sandstone.Two sodium chloride solutions(pH 4 and 8)were found to produce a clear distinction in wetting.Tests with identical fluid properties,differing only in wetting conditions,were compared.On flat surfaces,tests included adhesion and oillwater contact angles measured on altered surfaces.Imbibition and waterflood tests were conducted in cores.Imbibition rates confirm the relationship between wetting in the synthetic cores and on flat surfaces.Oil recovery efficiency is shown to depend on pore structure as well as on the wettability.
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