Summary
The rheology of foam fracturing fluids has been previously described as a yield-pseudoplastic fluid for a broad range of qualities, linear gel concentrations, and temperatures. With the increased use of foams for fracturing with higher proppant concentrations, crosslinking agents are often added. Because the viscous character of the external phase of the foam strongly influences the viscous properties of the foam, the viscosity of the foam will increase if the external phase is crosslinked.
Rheological properties of 25%- to 75%-quality N2 foams containing borate-crosslinked guar were measured on the recirculating flow-loop viscometer at temperatures from 75 to 300°F. When polymer was crosslinked in the foam, viscosity increased by factors of 3 to 10 or more over foams that contained only linear gel.
The fluid viscosity developed in a foam is a product of gas quality, external phase fluid viscosity, and crosslinking of the polymer in the external phase. The extent to which each of these factors is important depends upon both the quality and the concentration of the crosslinked polymer. Viscosity resulting from borate crosslinking is a stronger factor than either quality or linear polymer concentration. Borate crosslinking influence is greatest at low quality and at high polymer concentration.
