This paper discusses the chemical factors that operators must address to successfully substitute seawater for fresh water in borate-crosslinked guar fracturing fluids. Seawater contains cations and anions that affect the performance of the fracturing fluid's components, as well as the fluid's interaction with the formation.

Because seawater has high ionic strength, it lowers the viscosity obtained from borate-crosslinked guar. High magnesium in the water consumes hydroxide ions and affects pH control, which in turn affects the equilibrium borate-ion concentration. This paper addresses these problems and provides guidelines for borate fluid formulation to offset seawater characteristics for temperatures as high as 300°F.

Borate fluids from seawater can control fluid loss (FL) as well as freshwater borate fluids. Chemical gel breakers for offshore environments have been developed to help control the viscosity reductions in fracturing fluids. Conductivity values with seawater fluids are equal to or better than freshwater fluids. The presence of divalent cations in the seawater fluid caused no harm to the FL properties or the retained conductivity with borate seawater fluids.

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