Dual-mechanism thickening agents for hydraulic fracturing fluids

1. A dual-mechanism thickening agent comprising a gel-forming star macromolecule, wherein the gel-forming star macromolecule is represented by Formula (I):

wherein:

Core represents a crosslinked polymeric segment;

P1 represents a hydrophobic polymeric segment comprised predominantly of repeat units of monomeric residues of polymerized hydrophobic monomers;

P2 represents a hydrophilic polymeric segment comprised predominantly of repeat units of monomeric residues of polymerized hydrophilic monomers;

P3 represents a hydrophilic polymeric segment comprised predominantly of repeat units of monomeric residues of polymerized hydrophilic monomers;

P4 represents a hydroxyl-containing segment (homopolymeric or copolymeric) comprised of repeat units of monomeric residues, where at least one of the monomeric residues or a plurality of the monomeric residues is a hydroxyl-containing monomeric residue, of polymerized monomers;

P5 represents a hydrophilic polymeric segment comprised predominantly of repeat units of monomeric residues of polymerized hydrophilic monomers;

q1 represents the number of repeat units in P1 and has a value between 1 and 50;

q2 represents the number of repeat units in P2 and has a value between 30 and 2000;

q3 represents the number of repeat units in P3 and has a value between 30 and 2000;

q4 represents the number of repeat units in P4 and has a value between 1 and 50;

q5 represents the number of repeat units in P5 and has a value between 30 and 2000;

r represents the number of polymeric arms covalently attached to the Core;

s represents the number of hydroxyl-containing arms covalently attached to the Core; and

t represents the number of hydrophobic-containing copolymeric arms covalently attached to the Core and has a value of 1 or more.

2. The dual-mechanism thickening agent of claim 1 , wherein the gel-forming star macromolecule has a molecular weight of between 150,000 g/mol and 5,000,000 g/mol, the gel-forming star macromolecule forming a homogeneous gel when dissolved in water at a concentration of at least 0.05 wt. %, wherein the gel has:

i) a dynamic viscosity of at least 20,000 cP;

ii) a shear-thinning value of at least 10;

iii) an increase in dynamic viscosity of at least 5,000 cP in a 0.2 wt. % Borax aqueous solution, according to Borate-Crosslinker Thickening Test; or

iv) combinations thereof.

3. The dual-mechanism thickening agent of claim 1 , wherein the gel-forming star macromolecule has an increase in dynamic viscosity in the range of between 5,000 cP to 30,000 cP, or an increase in dynamic viscosity of at least 12%, in a 0.2 wt. % Borax aqueous solution, according to the Borate-Crosslinker Thickening Test, relative to the dynamic viscosity of a homogeneous gel of the star macromolecule with 0.0 wt. % Borax aqueous solution.

4. The dual-mechanism thickening agent of claim 1 , wherein the gel-forming star macromolecule has a viscosity of less than 5,000 cP at a shear rate of 4 sec −1 .

5. The dual-mechanism thickening agent of claim 1 , wherein the gel-forming star macromolecule has a PDI in the range of between 1.0 to 8.0.

6. The dual-mechanism thickening agent of claim 1 , wherein the gel-forming star macromolecule has a pH-induced break value of at least 50%.

7. The dual-mechanism thickening agent of claim 1 , wherein the gel-forming star macromolecule has an emulsion value of >12 hours.

8. The dual-mechanism thickening agent of claim 1 , wherein the gel-forming star macromolecule is a water-soluble mikto star macromolecule.

9. The dual-mechanism thickening agent of claim 1 , wherein the core comprises a hydrophobic crosslinked polymeric segment.

10. The dual-mechanism thickening agent of claim 1 , wherein the sum total number of arms (r+t) is between 3 and 1000, or the sum total number of arms (s+t) is between 3 and 1000, or both sum total number of arms (r+t) and sum total number of arms (s+t) are each between 3 and 1000.

11. The dual-mechanism thickening agent of claim 1 , wherein the molar ratio of r tot is in the range of between 8:1 and 3:1, or the molar ratio of s tot is in the range of between 8:1 and 3:1, or both the molar ratio of r to t and the molar ratio of s to t are each in the range of between 8:1 and 3:1.

12. The dual-mechanism thickening agent of claim 1 , wherein:

i) both q2 and q3 have a value greater than 100, and q2 is greater than q3; or

ii) both q5 and q3 have a value greater than 100, and q5 is greater than q3; or

iii) both q2 and q3 have a value greater than 100, and q5 and q3 have a value greater than 100, and q2 and q5 are greater than q3.

13. The dual-mechanism thickening agent of claim 1 , wherein

i) the molar ratio of r to s is in the range of between 40:1 and 1:40;

ii) the molar ratio of r to t is in the range of between 40:1 and 1:40;

iii) the molar ratio oft to s is in the range of between 40:1 and 1:40; or

iv) combinations thereof.

14. A composition, comprising the dual-mechanism thickening agent of claim 1 .

15. The composition of claim 14 , wherein the composition comprises at least 0.05 wt. % of the gel-forming star macromolecule.

16. The composition of claim 14 , wherein the composition is a fracturing fluid thickening additive, a drilling well fluid thickening additive, a gelling agent, or an additive to improve oil extraction from oil sands.

17. The composition of claim 14 , wherein the composition is a rheology-modifying composition having a shear-thinning value of at least 6.

18. The composition of claim 14 , wherein the composition further comprises one or more boric acid additives or borate-type additives.

19. The composition of claim 14 , wherein the gel-forming star macromolecule is prepared by one or more star macromolecule processes, comprising: one-pot process, the arm first process, ATRP, CRP, RAFT, TEMPO, Nitroxide, LRP, anionic polymerization, cationic polymerization, or combinations thereof.