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Viscoelastic surfactant (VES) fluids have been widely used in the oil industry as completion and stimulation fluids. The surfactants structurally arrange to form rod-like micelles that increase VES fluid viscosity for regular fracturing and frac-packing fluids. However, high fluid leak-off and low viscosities at elevated temperatures have limited VES fluids for hydraulic fracturing and frac-packing applications.
This paper will introduce a nanotechnology application for maintaining viscosity at high temperatures and controlling the fluid loss of VES fluid, without generating formation damage. The nanometer-scale particles studied display unusual surface morphologies and have high surface reactivity. These nanometer-scale particles, through chemisorption and surface charge attraction, associate with VES micelles to: 1) stabilize fluid viscosity at high temperatures; and 2) produce a pseudo-filtercake of viscous VES fluid that significantly reduces the rate of fluid loss and improves fluid efficiency. When internal breakers are used to break the VES micelles, the fluid will dramatically lose its viscosity and the pseudo-filtercake will then break into nanometer-sized particles. Since the particles are small enough to pass through the pore throat of producing formations, they will be flowed back with the producing fluids, and no damage will be generated. 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.