Viscoelastic surfactant (VES) systems are often used as viscosifiers for solids-free, high-viscosity pills used to control brine losses in production zones after perforation, gravel packing, or frac packs due to their non-damaging characteristics. Polymer gels have relatively higher rock retention values and often damage the invaded zone, so that acidization is required for removal. The VES systems behave as "equilibrium" or "living" polymers and their viscosity can be destroyed by contact with the produced hydrocarbons or with an internal breaker. This can eliminate the need for remedial treatments, greatly reducing operating cost/time and damage to the formation.

Historically, many VES systems have demonstrated limitations in high-density brines. Electrostatic screening generally reduces the viscosity or causes phase separation. Two methods have been found to stabilize VES packages in high-density completion brines: 1) by controlling the curvature of surfactant aggregates using low molecular weight surfactant polymers, nanometer scale manipulation of the phase behavior is achieved; and 2) VES gels have been developed using a mixture of oppositely charged surfactants to create gels in these high-density brines. By varying the ratios of surfactants it is possible to control micellar growth and the gel-like behavior. The interactions between the surfactants makes it possible to control the curvature and self-assembly on a nanometer scale, allowing the creation of polymer-like VES systems. The result is a greater variety of surfactants available to create gels in high-density completion brines.

This paper details the laboratory work performed to develop VES packages for fluids ranging from freshwater to high-density completion brines. Extensive rheology experiments on several fluids show the viscoelasticity of these systems. The self-breaking nature of VES systems when in contact with hydrocarbons or exposed to a built-in breaker has also been demonstrated.

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