Viscoelastic surfactant (VES) is widely known to be a clean fluid for fracturing and gravel pack application. However, its low thermal stability had made the VES inefficient for high-temperature application. VES viscosity dramatically declines when temperature exceeds 300°F. Work has been done to explore the potential of a new VES to apply to high-density, high-temperature applications. Such VES could also serve as alternate option to conventional polymer-based fracturing fluid, which is known to create some level of formation damage due to polymer residue.

This study aims to evaluate the fracturing fluid of a novel VES system that exhibits improved performance at high-temperature (300°F to 350°F) in high-density brines. Industries commonly use heavy brines of different densities; monovalent sodium bromide (NaBr) and sodium chloride (NaCl) and divalent calcium chloride (CaCl_2) and calcium bromide (CaBr2) brines were used for this evaluation. In this paper, we investigate the rheological properties and viscoelastic behavior of VES. A high-pressure/high-temperature (HP/HT) rheometer was used to evaluate the fluid viscosity stability, elastic modulus (〖G〗') and viscous modulus (〖G〗′) measurements at elevated temperature. Surface tension, breaker, and coreflood tests were conducted to assess the fluid’s flowback ability and formation damage extent using synthetic core. The sand-bearing capability of the VES as a fracturing fluid was examined via a high-temperature sand settling test.

Testing results demonstrated that this novel VES shows good shear recovery and viscosity stability with a 12.5-ppg (NaBr) brine system when tested at temperatures up to 325°F. The fluid system showed the ability to break with good retained permeability. The 11.5-ppg CaCl2 brine-based fluid developed its viscosity as the temperature increased. It showed good stability when tested at 350°F, and it can be broken with good retained permeability. Both brine-based viscoelastic fluids were found to be compatible with a demulsifier at a concentration up to 0.2% by volume.

In conclusion, this novel VES system could be formulated with NaBr and CaCl2 brines for high-density fracturing fluid application.

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