On-the-fly control of delayed borate-crosslinking of fracturing fluids

A method for controlling the delayed borate-crosslinking of a polysaccharide-based fracturing fluid, the method comprising:

• providing a polysaccharide;
• adding a first portion of a delay additive delay agent to the polysaccharide;
• hydrating the polysaccharide in the presence of the first portion forming a mixture of the hydrated polysaccharide and the first portion;
• adding a pH control agent to the mixture to render the fracturing fluid alkaline;
• adding a crosslinking agent to the mixture, wherein the crosslinking agent is capable of releasing at least one borate ion per molecule thereof in the fracturing fluid having an alkaline pH:
• determining a first delay time;
• comparing the first delay time to a preselected delay time;
• adding a second portion of the delay agent at a first rate to the fracturing fluid to provide a second delay time;
• and
• adding the delay agent on-the-fly during pumping sufficient to achieve the preselected delay time,
• wherein the delay agent is capable of complexing with the borate ions in the fracturing fluid having the alkaline pH.

A method for controlling the delayed borate-crosslinking of a polysaccharide-based fracturing fluid, the method comprising:

• providing a hydrated polysaccharide;
• adding a pH control agent to render the fracturing fluid alkaline;
• providing a pre-formed boron/delay agent complex in the fracturing fluid, wherein the complex is prepared by combining in an alkaline solution;
• a crosslinking agent, wherein the crosslinking agent is capable of releasing at least one borate ion per molecule thereof in an alkaline environment and
• a first portion of a delay agent, wherein the delay agent is capable of complexing with the borate ions in the alkaline environment;
• determining a first delay time;
• comparing the first delay time to a preselected delay time;
• adding a second portion of the delay agent at a first rate to the fracturing fluid to provide a second delay time;
• and
• adding the delay agent on-the-fly during pumping sufficient to achieve the preselected delay time.

A method for controlling the delayed borate-crosslinking of a polysaccharide-based fracturing fluid comprising:

• combining an aqueous solution of a hydrated polysaccharide containing cis-hydroxyl groups, an aqueous solution of crosslinking agent, wherein the crosslinking agent is capable of releasing at least one borate ion per molecule thereof in a fracturing fluid having an alkaline pH, and an aqueous solution of a pH control agent to render the fracturing fluid alkaline;
• adding a polyol delay agent at a first rate to the fracturing fluid to provide a first delay time, wherein the polyol delay agent is capable of complexing with the borate ions in the fracturing fluid having the alkaline pH and wherein the crosslinking agent and the polyol delay agent are added separately to the aqueous hydrated polysaccharide containing solution;
• determining the first delay time;
• comparing the first delay time to a preselected delay time;
• and
• adding the polyol delay agent on-the-fly during pumping sufficient to achieve the preselected delay time.

A method for controlling the delayed borate-crosslinking of a polysaccharide-based fracturing fluid comprising combining an aqueous solution of a polysaccharide containing cis-hydroxyl groups and a first portion of a polyol delay agent, the polyol delay agent being capable of complexing with borate ions in a fracturing fluid having alkaline pH;

• hydrating the polysaccharide in the presence of the first portion forming a mixture of the hydrated polysaccharide and the first portion;
• adding a pH control agent to the mixture to render the fracturing fluid alkaline;
• adding a crosslinking agent to the mixture, wherein the crosslinking agent is capable of releasing at least one borate ion per molecule thereof in a fracturing fluid having an alkaline pH;
• determining a first delay time;
• comparing the first delay time to a preselected delay time;
• adding a second portion of the polyol delay agent at a first rate to the fracturing fluid to provide a second delay time, and
• adding the delay agent on-the-fly during pumping sufficient to achieve the preselected delay time.

A method for controlling the delayed borate-crosslinking of a polysaccharide-based fracturing fluid, the method comprising combining

• an aqueous solution of a hydrated polysaccharide containing cis-hydroxyl groups, an aqueous solution of a pH control agent to render the fracturing fluid alkaline, and a preformed polyol boron/delay agent complex in the fracturing fluid, wherein the complex is prepared by combining in an alkaline solution a crosslinking agent, wherein the crosslinking agent is capable of releasing at least one borate ion per molecule thereof in an alkaline environment;
• and a first portion of a polyol delay agent, wherein the polyol delay agent is capable of complexing with the borate ions in the alkaline environment;
• determining a first delay time;
• comparing the first delay time to a preselected delay time;
• adding a second portion of the polyol delay agent at a first rate to the fracturing fluid to provide a second delay time;
• and
• adding the delay agent on-the-fly during pumping sufficient to achieve the preselected delay time.