Well treatment with complexed metal crosslinkers
Disclosed are compositions and methods for treating subterranean formations, in particular, oilfield stimulation compositions and methods using polymer viscosified fluid crosslinked with metal complexes with amino and/or phosphonic acids to provide an increased crosslinking temperature and a low pH sensitivity. The metal complexes can be used with borate crosslinkers to provide continuous viscosification as the temperature is increased.
1. A method of treating a subterranean formation penetrated by a well bore, the method comprising:
mixing into an aqueous mixture a crosslinkable, hydratable polymer and a delayed crosslinking agent, in amounts effective to obtain an aqueous mixture that can form a persistent gel at a crosslinking condition comprising an onset temperature of from 40° C. to 60° C.,
wherein the crosslinking agent comprises a complex comprising:
a metal,
a first ligand selected from the group consisting of amino acids, and salts or derivatives thereof, and
a second ligand selected from the group consisting of alkanolamines, alkoxides, and α-hydroxyacid derivatives,
wherein a molar ratio of the metal to the first ligand is from 1:1 to about 1:6, and a molar ratio of the metal to the second ligand is from 1:1 to about 1:10 and
injecting the aqueous mixture into the well bore; and
gelling the aqueous mixture at the persistent crosslinking condition.
2. The method of claim 1 , wherein the aqueous mixture is formed at a pH where a pH sensitivity slope of 5° C. per pH unit to 25° C. per pH unit can be observed for at least one pH unit range within a pH range from 8.5 to 12.5, the pH sensitivity slope (pHSS) being calculated according to the following formula:
pHSS =|( T XL1 −T XL2 )/( pH 2 −pH 1 )|
where pH 1 and pH 2 are lower and higher pH values, respectively, and T XL1 and T XL2 are the corresponding crosslinking temperatures for the respective pH value.
3. The method of claim 1 , wherein the metal is a Group 4 metal.
4. The method of claim 1 , wherein the persistent crosslinking condition comprises a pH between 10 and 10.5.
5. The method of claim 1 , further comprising adjusting the pH of the aqueous mixture by introducing a pH adjusting compound to control an onset temperature at which the gelling occurs.
6. The method of claim 1 , wherein the first ligand has from 2 to 40 carbon atoms and comprises an α-amino acid, an α-amino acid derivative, or a salt of an α-amino acid of the formula:
wherein R 1 and R 2 are independently selected from hydrogen and hydrocarbyl optionally containing a heteroatom, or together can form a substituted or unsubstituted cycloaliphatic bridge optionally containing a heteroatom;
wherein R 6 is hydrogen or a lone electron pair; and
wherein R 7 and R 8 are independently selected from hydrogen and substituted or unsubstituted aliphatic hydrocarbyl, or with one of R 1 and R 2 can form a substituted or unsubstituted cycloaliphatic bridge optionally containing a heteroatom.
7. The method of claim 6 , with the proviso that when both R 1 and R 2 are hydrogen, R 7 and R 8 are selected from hydrogen and substituted or unsubstituted aliphatic hydrocarbyl other than hydroxyalkyl.
8. The method of claim 6 , wherein R 7 and R 8 are both hydrogen.
9. The method of claim 6 , wherein at least one of R 1 and R 2 is carboxyalkyl.
10. The method of claim 1 , wherein the first ligand is derived from aspartic acid, glutamic acid or a combination thereof.
11. The method of claim 1 , wherein the first ligand has from 3 to 40 carbon atoms and comprises a β-amino acid, a β-amino acid derivative or a salt of a β-amino acid of the formula:
wherein R 1 and R 2 are independently selected from hydrogen and hydrocarbyl optionally containing a heteroatom, or together can form a substituted or unsubstituted cycloaliphatic bridge optionally containing a heteroatom;
wherein R 3 and R 4 are independently selected from hydrogen and hydrocarbyl;
wherein R 6 is hydrogen or a lone electron pair; and
wherein R 7 and R 8 are independently selected from hydrogen and substituted or unsubstituted aliphatic hydrocarbyl.
12. The method of claim 1 , wherein the first ligand is derived from beta-alanine.
13. The method of claim 1 , wherein the metal is titanium or zirconium.
14. The method of claim 1 , wherein the metal is a Group 4 metal, which is present in a concentration between 10 and 500 ppm by weight of the liquid phase of the aqueous mixture.
15. The method of claim 1 , wherein the crosslinkable polymer is selected from the group consisting of polysaccharides.
16. The method of claim 1 , wherein the crosslinkable polymer is selected from the group consisting of ionically modified galactomannan, cellulose and starch.
17. The method of claim 1 , further comprising introducing proppant into the aqueous mixture.
18. The method of claim 1 , further comprising introducing into the aqueous mixture a borate crosslinker for reversible crosslinking at a temperature below 40° C.
19. The method of claim 1 , further comprising introducing a clay stabilizer and a surfactant into the aqueous mixture.
20. The method of claim 19 , wherein the polymer is ionically modified to introduce a cationic or anionic moiety and the surfactant comprises an oppositely charged moiety.
21. The method of claim 1 , further comprising introducing tetramethyl ammonium chloride and a surfactant into the aqueous mixture.