Method of removing water-based filter cake

Abstract

A method of removing a water-based filter cake from a wellbore, the method comprising: contacting the filter cake with a mixture comprising: a non-aqueous, polar solvent; an agent selected to breakdown the filter cake; said mixture comprising <5 wt % water and preferably being essentially anhydrous. The low water content of the mixture actually slows the degradation of the filter cake which has surprisingly been found to be more effective as it allows a more even removal of the filter cake and a more efficient use of the mixture; without the tendency to create local holes in the filter cake where the mixture could escape. Embodiments of the present invention use a polar solvent with a dielectric constant of more than (15), preferably more than (30) such as (15) monoethylene glycol (MEG). In preferred embodiments the agent comprises a salt based on potassium EDTA (ethylenediaminetetraacetic acid).

Dependencies are inferred from the claim text.