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Viscoelastic surfactant (VES) fluids have been widely used as gravel-packing, frac-packing and fracturing fluids for more than a decade because the fluids exhibit excellent rheological properties and maintain low formation damage characteristics compared with crosslinked-polymer fluids. Due to its non-wall-building property, VES fluid has much higher fluid leak-off into the reservoir matrix than wall-building polymer fluid. For frac-packing this has limited VES use to reservoirs with permeability of less than 1000 md and, in most cases, less than 250 md. Excessive fluid leak-off also significantly increases the cost of treatment.
This paper will introduce new technology for controlling the fluid loss of VES fluids to about 300ºF. New fluid loss control agents have been developed that, through chemisorption and surface charge attraction, associate with VES micelles to produce a pseudo-filtercake of viscous VES fluid that significantly reduces the rate of fluid loss. Use of this technology will reduce the VES fluid volume required for a given treatment by up to two-thirds and extends the permeability range of VES fluids to about 2000 md. The fluid loss control agents are slowly water-soluble particles that are used at relatively low concentrations. The particles will be dissolved and/or flowed back with the producing fluid. The rate of the pseudo-filtercake clean-up is enhanced by use of internal VES breakers. The results of rheology, leak-off, and core flow tests will be presented for the VES fluid systems at temperatures 150°F and 250°F.