Bimal Parekh's thesis
by
Bimal Parekh, MSE
University of Texas at Austin, 2003
Supervisor: Mukul M. Sharma
Poor gas flow performance is observed in depleted low permeability reservoirs after some well
operations such as completions and workovers. The use of aqueous treatment fluids often results
in ‘water block’ due to less than desirable recovery of the ‘leak off’ fluids. This curtails
the well deliverability due to reduced relative permeability to gas/oil in invaded region.
This simulation study aims at analyzing the effect of various factors governing the cleanup of
water-blocks in fractured and unfractured wells for both gas as well as oil reservoirs. The
effects of drawdown, capillary pressure, relative permeability, and heterogeneity as well
as the influence of fracture geometry on the recovery of well deliverability following some
well operations such as fracturing have been examined.
An attempt is made to identify the key parameters that influence the cleanup of water-blocks.
Drawdown, fracture length and shapes of relative permeability curves strongly affect the
recovery in productivity. On the other hand, end points of relative permeability curves and
horizontal well length have insignificant impact on the cleanup. Higher vertical permeability
favors early recovery of productivity in ‘high perm’ layer and delays cleanup of water-blocks
in ‘low perm’ layer.
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 of the water-blocks more rapidly in depleted low-permeability
reservoirs.
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