Page 198 - Gas Wettability of Reservoir Rock Surfaces with Porous Media
P. 198

182     Gas Wettability of Reservoir Rock Surfaces with Porous Media














                                    (A)                             (B)











                                                     (C)
          FIGURE 5.15
          Effect of gas wettability on gas/water distribution and gas recovery. (A) Nongas-wetting, (B) neutral-gas-wetting, and (C) preferential-
          gas-wetting.


                            5.2.2.2 EFFECTS OF GAS WETTABILITY ON GAS/WATER DISTRIBUTION
                            Nongas-wettability model: From Fig. 5.15A, it can be seen that in the nongas-
                            wettability model, water displaces gas mainly through capillary force.
                            Increasing radius, decreasing capillary force, and slowing of flow speed in
                            pores enable the pores to capture huge amounts of gas. As displacement pro-
                            gresses, the viscous force of water drives gas. Some gas enters the channels,
                            while some disperses as gas beads, which are distributed in channels. A layer
                            of wetting film is formed on the pore walls, and water shrinks into irregular
                            water beads or drops, in local areas with thicker films.

                            Neutral-gas-wettability model: From Fig. 5.15B, it can be seen that in the
                            neutral-gas-wetting model, water-displacing gas is more complete. Water
                            almost saturates the entire model, and only a little gas remains.
                            Preferential-gas-wettability model: From Fig. 5.15C, it can be seen that in the
                            preferential-gas-wetting model, water can be found in the center of the chan-
                            nels after water displaces gas, and gas forms a film on the pore walls.



                            5.2.3   Gas Wettability of Gas/Oil System Studied With
                            Etched Glass Network Model
                            The gas wettability of the gas/oil system of the same solid surface is weaker
                            than that of gas/water system. During the experiment, it is found that when
                            single-straight capillaries and etched glass network models are treated with
   193   194   195   196   197   198   199   200   201   202   203