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74      Gas Wettability of Reservoir Rock Surfaces with Porous Media



                                 different concentrations of fluorocarbon polymer Zonyl8740 solution is
                                 taken as the measuring matrix.
                               2. Experimental Method
                                    The glass slide is first washed with ethyl alcohol and then with dis-
                                 tilled water. After drying under high pressure nitrogen, it is immediately
                                 put into Zonyl8740 solutions of varying concentrations before it is
                                 taken out, sealed, and dried after soaking for 4 hours. Contact angle of
                                 air bubble and n-octane with water is measured with a contact angle
                                 meter under an atmospheric pressure at 20 C. The size of bubbles and

                                 liquid drops are all 5 μL.
                               3. Experimental Result and Discussion
                                    The glass slide/water interface free energy (γ glass slide-water ), free energy
                                 (γ glass slide ) of glass slide surface, and work of adhesion (A) in the bub-
                                 ble capture method can be obtained by combining the values obtained
                                 from indoor experiments of contact angles of bubbles of glass slide trea-
                                 ted with Zonyl8740 solutions of varying concentrations and liquid in
                                 distilled water, and the theoretical derivation in Section 4.2.2. See
                                 Table 2.14 for the contact angle measured from experiments and calcu-
                                 lated interface free energy.
                            Table 2.14 shows that as the Zonyl8740 concentration increases, work of
                            adhesion A gradually reduces. The contact angles of bubbles and n-octane liq-
                                                                            3
                            uid drops (θ Air and θ Oct ) decrease when θ Air . θ Oct . 90 . This illustrates that as
                            Zonyl8740 concentration increases, gas-wetting capability is enhanced and the
                            order of wetting degree of glass slide caused by air, water, and n-octane is
                            air , n-octane , water. Although the liquid phase preferentially wets solid sur-
                            face with respect to gas, the wettability of solid surface caused by gas can’tbe
                            ignored. When work of adhesion is reduced, the contact angle of gas can be
                            less than 90 degrees. At this stage, γ SV  , γ SW , i.e., gas has stronger capability to
                            reduce surface energy of solid compared to liquid. This research conclusion is
                            consistent with the actual experimental result of King R. N. [37].


                            2.4.3   Effect of the Nature of Measuring Matrix on Gas
                            Wettability
                            All the above sections use quartz glass slides treated with cationic fluorocar-
                            bon polymer Zonyl8740 solutions of different concentrations as a measuring


           Table 2.14  Contact Angle of Air Bubble and Liquid Drop of n-Octane
           C Zonyl8740 wt%    θ Air 3     θ Oct 3      γ SW  mJ=m 2    γ SV  mJ=m 2    A mJ=m 2

           0.02               166.36      144.65         2.260           72.33           70.07
           0.04               152.48      132.02         4.476           68.413          63.95
           0.06               135.84      125.36         3.726           55.45           51.73
           0.1                135.52      122.54         4.56            56.00           51.45
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