Encapsulated internal filter cake breakers with improved release properties
A wellbore fluid including a peroxide degradable polymer and an encapsulated peroxide source. The peroxide degradable polymer may be a polysaccharide. The peroxide source may include an inorganic peroxide, including zinc and alkaline earth metal peroxides, such as magnesium peroxide. The encapsulating material may be a polymer, including a metal crosslinked acrylic polymer. The release of peroxide, from peroxide sources generally, can be controlled by means of pH such that peroxide source can be activated, and peroxide released, by a change in pH. In a wellbore, this pH change can be effected by using produced fluids to lower the pH of a more basic wellbore fluid.
1. An encapsulated internal breaker for the removal of a filter cake from a wellbore in a subterranean formation, the encapsulated internal breaker comprising:
i a filter cake breaker, the filter cake breaker being magnesium peroxide, zinc peroxide, or an alkaline earth metal peroxide,
ii an anti-caking agent, the anti-caking agent being magnesium carbonate, calcium carbonate, colloidal silica micro particles, or clay particles, and
iii an encapsulation film that encapsulates the filter cake breaker, the encapsulation film comprising a magnesium-, calcium-, copper-, aluminium- or zinc-crosslinked acrylic polymer which is insoluble in well bore fluids having a pH value equal to or greater than 7.5.
2. The encapsulated internal breaker of claim 1 wherein the metal-crosslinked acrylic polymer is the zinc-crosslinked acrylic polymer.
3. The encapsulated internal breaker of claim 1 wherein the water soluble polymer is present in an amount of from 1 to 5 weight percent based on the total weight of the encapsulated internal breaker.
4. The encapsulated internal breaker of claim 1 wherein the metal-crosslinked acrylic polymer is the zinc-crosslinked acrylic polymer having a weight percent of zinc crosslinked from 33% to 50%.
5. The encapsulated internal breaker of claim 1 wherein the magnesium-, calcium-, copper-, aluminium- or zinc-crosslinked acrylic polymer has a Tg equal to or greater than 45° C.
6. The encapsulated internal breaker of claim 1 further comprising a water-soluble polymer as a binder.
7. A wellbore fluid comprising a degradable polymer and an encapsulated internal breaker, wherein the encapsulated internal breaker comprises:
i a filter cake breaker, the filter cake breaker being magnesium peroxide, zinc peroxide, or an alkaline earth metal peroxide,
ii an anti-caking agent, the anti-caking agent being magnesium carbonate, calcium carbonate, colloidal silica micro particles, or clay particles, and
iii an encapsulation film that encapsulates the filter cake breaker, the encapsulation filing comprising a magnesium-, calcium-, copper-, aluminium- or zinc-crosslinked acrylic polymer which is insoluble in well bore fluids having a pH value equal to or greater than 7.5.
8. The well bore fluid of claim 7 wherein
i the filter cake breaker is magnesium peroxide,
ii the anti-caking agent is calcium carbonate, and
iii the encapsulation film includes the zinc-crosslinked acrylic polymer.
9. The well bore fluid of claim 7 further comprising a water-soluble polymer as a binder.
10. A process for the removal of a filter cake from a wellbore in a subterranean formation comprising the steps:
a adding one or more degradable polymer to a wellbore fluid;
b adding an encapsulated internal breaker to a wellbore fluid;
c pumping said wellbore fluids into the wellbore; and
d changing the pH of the fluid in the wellbore so as to activate the degradable polymer;
wherein the encapsulated internal breaker comprises:
i an filter cake breaker, the filter cake breaker being magnesium peroxide, zinc peroxide, or an alkaline earth metal peroxide,
ii an anti-caking agent, the anti-caking agent being magnesium carbonate, calcium carbonate, colloidal silica micro particles, or clay particles, and
iii an encapsulation film that encapsulates the filter cake breaker, the encapsulation filing comprising a magnesium-, calcium-, copper-, aluminium- or zinc-crosslinked acrylic polymer which is insoluble in well bore fluids having a pH value equal to or greater than 7.5.
11. The process of claim 10 wherein
i the filter cake breaker is magnesium peroxide,
ii the anti-caking agent is calcium carbonate, and
iii the encapsulation film includes the zinc-crosslinked acrylic polymer.
12. The process of claim 10 wherein the encapsulated internal breaker further comprises a water-soluble polymer as a binder.