Many people have noted cases where significant production is lost after shutting in a well following a partial clean-up after a frac. Sometimes the damage occurs even when the well has been flowing steadily for a long period of time (months or even years). As always, there are also cases where a shut-in has seemed to improve production after a frac.

The reasons for this apparently contrary behavior may lie in fundamental concepts of relative permeability hysteresis and capillary pressure. Theoretical reasons for increased damage resulting from well shut-ins after partial post-frac clean-up will be discussed. Conditions where shut-ins can be beneficial will also be discussed, should anyone be fortunate enough to encounter them. Methods to help minimize damage from the identified mechanisms will also be mentioned.