Wettability alteration and water blocking

Water blocking and wettability alteration are related acidizing damage mechanisms, especially useful in sandstones. In tight formations, water that is introduced to the formation may be retained by capillary forces. Gas or oil production rates may be severely impaired. Proper selection of surfactant additives is necessary to avoid water blocking. This is quite often difficult to assess without the benefit of core flow testing with a representative formation core. 

Concrete dampproofers are integral admixtures that alter the concrete surface so that it becomes water repellent, or less wettable . This is illustrated in Fig. 4.1, which shows a close up of a water drop on a surface of a concrete that has had a dampproofer incorporated into it. This water repellency conferred on the concrete is only effective in preventing water from entering the surface when the applied pressure is small, e.g. rainfall in windy conditions, or capillary rise. The latter effect is shown in Fig. 4.2. In view of this, these materials are used normally for improving the quality of concrete pavers, tiles, bricks, blocks and cladding panels where the additional benefits of reduced efflorescence, the maintenance of clean surfaces and the more even drying out of adjacent bricks and panels are also obtained. 

H2S reacting with nickel can block electrochemically active sites for the hydrogen oxidation, can change the wettability of the anode toward carbonates, can modify the anode surface and its porous structure, can alter the anode conductivity, can change the carbonate conversion to sulfate and can poison catalytic sites for the water gas shift reaction. 

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