Produced water borate crosslinking compositions and method of use
A composition and method for treating a fracturing fluid comprising produced water with high levels of dissolved solids using a polymer crosslinked with a boron compound and a high pH alkylamine buffer. The composition improves the viscosity stability of the fracturing fluid at elevated bottom-hole temperatures, particularly when the fluid has high levels of calcium and magnesium. The composition is particularly useful with polysaccharides, including galactomannan gums, such as guar gum, locust bean gum, and karaya gum, and allows for the use of the preferred boron compound crosslinkers in high total dissolved solids fracturing fluids without the pH destabilization problems encountered with the prior art.
1. A method of treating a fracturing fluid to maintain a stable crosslink viscosity, the method comprising:
providing a fracturing fluid comprising produced waters and having a total dissolved solids level greater than 1,500 ppm;
adding a polysaccharide to the fracturing fluid to hydrate the polysaccharide;
adding an alkylamine pH buffer to the fracturing the fluid, the alkylamine pH buffer being capable of maintaining the fracturing fluid at a pH level greater than 9.0 at temperatures greater than about 80° F.;
adding a secondary alkaline pH buffer to the fracturing fluid;
adding a boron crosslinking compound to the fracturing fluid;
wherein the alkylamine pH buffer and the secondary alkaline pH buffer are not added until after the polysaccharide has had sufficient time to hydrate in the fracturing fluid.
2. The method of claim 1 wherein the polysaccharide is mixed with oil to form a slurry comprising about 3-5 pounds of polysaccharide per gallon of slurry prior to adding to the fracturing fluid.
3. The method of claim 2 wherein about 4 to 6 gpt polysaccharide slurry, about 0.4 to 0.6 gpt boron compound, and about 0.5 to 3.5 gpt alkylamine are added to the fracturing fluid.
4. The method of claim 2 wherein the boron crosslinking compound is mixed with a secondary pH buffer having an alkaline pH to form a crosslinker-buffer solution prior to adding to the fracturing fluid.
5. The method of claim 4 wherein about 4 to 6 gpt polysaccharide slurry, about 1.5 to 4 gpt crosslinker-buffer solution, and about 0.5 to 3.5 gpt alkylamine are added to the fracturing fluid.