Drilling and maintenance fluids that leave a easily removable filter cake

摘要

The invention provides alkaline water base well drilling and servicing fluids which deposit an easily degradable and removable filter cake on the sides of a borehole during well drilling and servicing operations. The fluids contain one or more polysaccharide polymers, sized bridging particles, and a peroxide selected from the group consisting of alkaline earth metal peroxides, zinc peroxide, and mixtures thereof. The fluids deposit a filter cake containing the peroxide. The invention also provides processes for enhancing the removal of the filter cake which comprises depositing a peroxide-containing filter cake on the sides of the borehole, or on the filter cake already present on the sides of the borehole, and thereafter contacting the peroxide-containing filter cake with an acidic solution to activate the peroxide which thereafter degrades the polysaccharide polymers in the filter cake. Preferably the filter cake containing the degraded polymer is washed with a fluid in which the bridging particles are soluble to remove the entire filter cake(s) from the sides of the borehole.