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 b