Self-Cleaning Drill-in Fluid Filter Cake 

Filter cake arising from the drilling fluid used in the drilling process coats the face of the  wellbore.  Removal of this damage, especially in long horizontal/directional open hole sections is normally a critical part of achieving optimal well performance (either production or injection).

Typically mud cake damage is removed by filling the open hole section with a clean up fluid that attacks the filter cake, such as Cleansorb's Arcasolve^TM mud damage removal formulations.  These produce acid after the fluid is placed into the wellbore, ensuring excellent zonal coverage. 

In some situations, ensuring that the treatment fluid effectively contacts the filter cake on the wellbore face can present challenges.  his includes wells with gravel packed (GP) completions or other types of screen/slotted liners including expandable sand screens. Special completions enabling the annulus between the tubing and the formation to be filled with treatment fluid may be employed.  Alternatively, careful control of the treatment fluid density, relative to completion fluid already in the hole, and use of overbalance pressure can be used to influence fluid flow towards the formation face. 

Where placement of a treatment fluid is difficult, an ideal solution would be to deposit a filter cake which cleaned up within a reasonable timescale with no intervention.  

To aid filter cake cleanup in the more difficult situations presented by GP, screen or slotted liner completions Cleansorb has developed a speciality drilling additive.  This product is added to the drill-in fluid used to drill open hole section and becomes incorporated into the filter cake.  Over a period of several days this additive dissolves to uniformly disrupt the filter cake.  The dissolution produces acid within the filter cake so may also dissolve acid soluble material within the filter cake.

Excellent cleanup and restoration of permeability may be obtained with no intervention needed. 

The additive may also be incorporated into the gravel pack fluid, the completion fluid left in the hole before running screens or liner, or in the actual screen or liner.  If desired, Arcasolve fluid including polymer breakers may also be used to ensure complete cleanup of all drill-in fluid components.