Wettability alteration used for water block prevention in high-temperature gas wells ///
Water accumulation near the wellbore or fracture face can decrease the relative permeability of oil and gas. This restriction to oil and gas flow, due to increased water saturation, is called water block. Sources for excess formation water could be water-based fluids used in drilling, completion, matrix or fracture treatments; cross-flow of water to dry gas zones; or water imbibition into tight zones. The excess water is trapped in the formation, due to high capillary pressure in porous rock and viscous fingering of gas through water. The presence of clays, migrating fines, reservoir heterogeneity and other forms of formation damage, such as wettability alterations, can increase the severity of trapping.
Laboratory studies by Kamath and Laroche, and Mahadevan and Sharma, have shown that removal of water from the formation occurs in two stages—an initial displacement stage where water is expelled from the core, followed by a long-term evaporation stage.
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