Cellulose nanofibers in extended cement systems
Methods herein may include injecting a cement slurry having an aqueous base fluid, a cement, and a plurality of cellulose nanofibers dispersed in the aqueous base fluid. The plurality of cellulose nanofibers may be present in the slurry in an amount effective to provide a slurry density of not higher than 15 lb/gal.
1. A method for treating a subterranean formation penetrated by a wellbore, the method comprising:
injecting a cement slurry having a slurry viscosity into the wellbore, the slurry comprising:
an aqueous base fluid having an aqueous base fluid viscosity;
a cement; and
a plurality of cellulose nanofibers having a surface packed with a plurality of hydroxyl groups dispersed in the aqueous base fluid,
modifying or converting the plurality of hydroxyl groups with sulfate or phosphate ester groups and/or by carboxylation so that the cellulose nanofibers are initially inactive, wherein the cellulose nanofibers do not increase the slurry viscosity or the aqueous base fluid viscosity more than about 1.05 times;
activating said cellulose nanofibers via a trigger to increase yield stress of the cement slurry and/or the slurry viscosity, wherein a density of the cement slurry does not exceed 15 lb/gal; and
setting the cement slurry.
2. The method of claim 1 , further comprising performing a downhole operation.
3. The method of claim 1 , wherein the injecting comprises pumping the cement slurry through the wellbore and into an annulus formed between the wellbore and a casing.
4. The method of claim 1 , wherein the density of the cement slurry ranges from about 6 to about 15 lb/gal.
5. The method of claim 1 , wherein the plurality of cellulose nanofibers further increases a slurry yield by 1 to 3 cubic feet per sack depending on the density of the cement slurry.
6. The method of claim 1 , wherein the plurality of cellulose nanofibers is present in the cement slurry in a concentration ranging from about 0.03 to about 6% by weight of a blend.
7. The method of claim 1 , wherein the cellulose nanofibers are selected from the group of cellulose nanofibrils and cellulose nanocrystals.
8. The method of claim 1 , wherein the cellulose nanofibers have a length ranging from about 100 nm to about 3 mm.
9. The method of claim 1 , wherein the cellulose nanofibers have a diameter ranging from about 4 nm to about 20 μm.
10. The method of claim 1 , wherein the cement slurry further comprises at least an additive selected from the group of fly ash, silica, cenospheres, a dispersant, a retarder, an antifoaming agent, a fluid loss control additive or a combination thereof.
11. The method of claim 1 , wherein the cement slurry further comprises a gas and a foaming agent.
12. The method of claim 1 , wherein the trigger is activated and the cellulose nanofibers form a single-phase colloidal suspension or gel.
13. The method of claim 1 , wherein the cellulose nanofibers are cellulose nanofibrils and a concentration of cellulose nanofibrils in the cement slurry increases at least 0.1% by weight of a blend of all solid materials in the cement slurry.
14. The method of claim 1 , wherein the cellulose nanofibers are cellulose nanocrystals and a concentration of cellulose nanocrystals in the cement slurry increases at least 0.25% by weight of a blend of all solid materials in the cement slurry.
15. A method for treating a subterranean formation penetrated by a wellbore, the method comprising:
injecting a cement slurry having a slurry viscosity into the wellbore, the slurry comprising:
an aqueous base fluid having an aqueous base fluid viscosity;
a cement; and
a plurality of cellulose nanofibers having a surface packed with a plurality of hydroxyl groups dispersed in the aqueous base fluid,
modifying or converting the plurality of hydroxyl groups with sulfate or phosphate ester groups and/or by carboxylation so that the cellulose nanofibers are initially inactive, wherein an initial addition of the plurality of cellulose nanofibers to the aqueous fluid does not raise a viscosity of the cement slurry by more than 1.05 times;
activating said cellulose nanofibers by reaching a target treatment zone, temperature or shear rate, wherein the cellulose nanofibers form a single-phase colloidal suspension; and
setting the cement slurry.
16. The method of claim 15 , wherein the cellulose nanofibers are cellulose nanofibrils and a concentration of cellulose nanofibrils in the cement slurry increases at least 0.1% by weight of a blend of all solid materials in the cement slurry.
17. The method of claim 15 , wherein the cellulose nanofibers are cellulose nanocrystals and a concentration of cellulose nanocrystals in the cement slurry increases at least 0.25% by weight of a blend of all solid materials in the cement slurry.