Rate enhancement in unconventional gas reservoirs by wettability alteration

In unconventional water-wet gas reservoirs with extremely low permeability, water blockage due to the capillary end effect near the fracture face and in the wellbore vicinity is a severe obstacle to gas production. Wettability alteration of rock surface is discussed as an effective way to reduce water blockage and enhance gas production. It can also be applied to accelerating dewatering and preventing drilling and fracturing fluid leak-off. The current paper develops analytical models for steady-state two-phase linear and radial flows, accounting for the contact-angle-dependent capillary pressure and relative permeability. The model has been validated by comparison with laboratory test. Applications of the proposed model to porous media with constant and piecewise-constant contact angles are presented. The modelling shows that the competition between the viscous and capillary effects on productivity results in an optimal contact angle for the maximum well productivity indexes for water and gas. The productivity index increases with the capillary-viscous ratio and the altered zone length. (C) 2015 Elsevier B.V. All rights reserved.