Poor gas inflow performance is observed in some depleted, low permeability, reservoirs after completion and workover operations. The use of aqueous treatment fluids often results in a ‘water block' due to poor recovery of the fluids that have leaked-off. This curtails well deliverability due to reduced relative permeability to gas/oil in the invaded region.

This study analyzes the effect of various factors governing the cleanup of water blocks in fractured and un-fractured wells for both gas and oil reservoirs. The effects of drawdown, capillary pressure, relative permeability, and heterogeneity as well as the influence of fracture geometry on well deliverability following some well operations, such as fracturing, have been examined by detailed simulations.

Drawdown, fracture length and shapes of relative permeability curves strongly affect the recovery in productivity. On the other hand, end point relative permeabilities and horizontal well length have an insignificant impact on cleanup. Higher vertical permeabilities favor early recovery of well productivity in ‘high perm' layers and delay cleanup of water blocks in ‘low perm' layers.

The results suggest the need to lower capillary pressure by reducing interfacial tension and/or altering wettability of the rock surface from strongly water-wet to intermediate-wet. With the correct selection of treatment fluids, proper design of fracture geometry and optimum drawdown applied it is possible to cleanup water blocks more rapidly in depleted low-permeability reservoirs.