Zirconium-based cross-linking composition for use with high pH polymer solutions
View Patent ↗A cross-linking composition comprising (a) an aqueous liquid; (b) a pH buffer; (c) a cross-linkable organic polymer; and (d) a solution of a zirconium cross-linking agent comprising the product of contacting a zirconium complex with an alkanolamine and ethylene glycol wherein the mole ratio of alkanolamine to zirconium is 2:1 to 4:1 and the mole ratio of ethylene glycol to zirconium is 1:1 to 10:1. Optionally, water, hydroxyalkylated ethylenediamine, or both are added to the zirconium complex. The cross-linking composition of this invention is useful in oil field applications, for example, for hydraulically fracturing a subterranean formation and for plugging permeable zones or leaks in a subterranean formation.
1. A cross-linking composition comprising (a) an aqueous liquid; (b) a pH buffer; (c) a cross-linkable organic polymer; and (d) a zirconium cross-linking agent comprising the product of contacting a solution of a zirconium complex with an alkanolamine and ethylene glycol as an accelerator wherein the mole ratio of alkanolamine to zirconium is 2:1 to 4:1 and the mole ratio of ethylene glycol to zirconium is 1:1 to 10:1 wherein the cross-linking composition has a crosslinking rate in the range of 3-8 minutes, providing an initial viscosity of at least 650 Cp, and a viscosity of at least 350 Cp after 90 minutes, further wherein, if the zirconium complex is contacted with water, water acts as a rate retarder, and water is added in an amount to provide a mole ratio of water to zirconium of 1:1 to 20:1.
2. The composition of claim 1 wherein the zirconium complex is further contacted with water at a mole ratio of water to zirconium of 1:1 to 20:1.
3. The composition of claim 1 or 2 wherein the zirconium complex is further contacted with a hydroxyalkylated ethylenediamine at a mole ratio of greater than 0 up to 2:1 of hydroxyalkylated ethylenediamine to zirconium.
4. The composition of claim 3 wherein the hydroxyalkylated ethylenediamine is N,N,N′,N′-tetrakis-(2-hydroxypropyl)ethylenediamine.
5. The composition of claim 1 wherein the alkanolamine is selected from the group consisting of triethanolamine, triisopropanolamine, and tri-n-propanolamine.
6. The composition of claim 5 wherein the alkanolamine is triethanolamine.
7. The composition of claim 1 wherein the zirconium complex is tetra-1-propyl zirconate, tetra-n-propyl zirconate, or tetra-n-butyl zirconate.
8. The composition of claim 7 wherein the zirconium complex is tetra-n-propyl zirconate.
9. The composition of claim 1 wherein the cross-linking composition provides a viscosity in the range of 350 to 1000 Cp after 90 minutes.
10. The composition of claim 1 wherein the cross-linking composition provides an initial viscosity of at least 750 Cp, and a viscosity of at least 500 Cp after 90 minutes.