Process to prepare borozirconate solution and use as cross-linker in hydraulic fracturing fluids

A cross-linking composition which comprises (a) an aqueous liquid;

• (b) a pH buffer;
• (c) a cross-linkable organic polymer;
• and (d) a borozirconate solution prepared by a process which comprises:
• (1) contacting a zirconium complex with a first alkanolamine at a ratio of 1 to 10 moles of the first alkanolamine per mole of zirconium in an alcohol to form a first mixture;
• (2) adding glycerol and water to the first mixture at a ratio of about 0.1 to 1 moles of glycerol per mole of zirconium and at a ratio of 1 to 12 moles of water per mole of zirconium to form a second mixture;
• (3) contacting the second mixture with a solution of a boron compound and a second alkanolamine in an alcohol, at a ratio of 1 to 6 moles of boron per mole of zirconium and 1 to 4 moles of the second alkanolamine per mole of boron and at a temperature of 25° C. to 90° C. for a period of time sufficient to stabilize the resulting borozirconate solution.

A method for hydraulically fracturing a subterranean formation, which comprises introducing into the formation at a flow rate and pressure sufficient to create, reopen, and/or extend one or more fractures in the formation, a cross-linking composition comprising an aqueous liquid;

• a pH buffer;
• a cross-linkable organic polymer, and a solution of a borozirconate complex wherein the solution is prepared by a process comprising (a) contacting a zirconium complex with a first alkanolamine at a ratio of 1 to 10 moles of the first alkanolamine per mole of zirconium in an alcohol to form a first mixture;
• (b) adding glycerol and water to the first mixture at a ratio of about 0.1 to 1 moles of glycerol per mole of zirconium and at a ratio of 1 to 12 moles of water per mole of zirconium to form a second mixture;
• (c) contacting the second mixture with a solution of a boron compound and a second alkanolamine in an alcohol, at a ratio of 1 to 6 moles of boron per mole of zirconium and 1 to 4 moles of the second alkanolamine per mole of boron and at a temperature of 25° C. to 90° C. for a period of time sufficient to stabilize the resulting borozirconate solution.

A method for selectively plugging permeable zones and leaks in subterranean formations which comprises introducing into the permeable zone or the site of the subterranean leak, a cross-linking composition comprising an aqueous liquid;

• a pH buffer, a cross-linkable organic polymer;
• and an aqueous solution of the borozirconate complex comprising an aqueous liquid;
• a pH buffer;
• a cross-linkable organic polymer, and a solution of a borozirconate complex wherein the solution is prepared by a process comprising (a) contacting a zirconium complex with a first alkanolamine at a ratio of 1 to 10 moles of the first alkanolamine per mole of zirconium in an alcohol to form a first mixture;
• (b) adding glycerol and water to the first mixture at a ratio of about 0.1 to 1 moles of glycerol per mole of zirconium and at a ratio of 1 to 12 moles of water per mole of zirconium to form a second mixture;
• (c) contacting the second mixture with a solution of a boron compound and a second alkanolamine in an alcohol, at a ratio of 1 to 6 moles of boron per mole of zirconium and 1 to 4 moles of the second alkanolamine per mole of boron and at a temperature of 25° C. to 90° C. for a period of time sufficient to stabilize the resulting borozirconate solution.