Abstract
Micellar fluids with viscoelastic behavior, or viscoelastic surfactant fluids, are used in the oil industry as completion and stimulation fluids. The viscoelastic (i.e. viscous and elastic) behavior of these fluids is based on the overlap and entanglement of very long worm-like-micelles. High fluid leak-off has, however, limited their application for hydraulic fracturing and frac-packing applications. Recent developments have found that micellar fluids can have wall-building leak-off control similar to crosslinked-polymer fluids (CPF) by the addition of a small amount of inorganic crystals that are less than 100 nanometers in size (i.e. nanoparticle).
This paper will investigate the mechanism of fluid loss control for the particle-micellar fluid system. The tiny particles have high surface force, including van der Waals and electrostatic forces. The nanoparticle surface forces pseudo-crosslink the elongated micelles, which is similar to crosslinking polymers. The unique pseudo-crosslinking of surfactant micelles and particles has demonstrated improved viscosity, the formation of a filter cake, and enhanced thermal stability. Laboratory tests show the development of a filter cake significantly reduces the rate of fluid loss and demonstrates wall-building rather than viscosity-dependant leak-off control. Two models of static fluid loss control for particle-polymer fluid system will be reviewed. Fluid leakoff characteristics will be compared between the particle-micellar fluid system and particle-polymer fluid system.
Uniqueness of this system is that the fluid loss control was achieved without compromising the internal breaking efficacy. Ordinarily additives 'plasticize' the micellar or colloidal aggregates. However, through our patented processes, we were able to successfully place the internal breakers inside the elongated micelles so as to not interfere with particles' pseudo-crosslinking. When internal breakers are activated by temperature, the elongated micelle structure collapses thereby significantly reducing the fluid viscosity and thus breaking down the filter cake into tiny particles. This results in clean breaking gel with reduced damage to formation permeability and fracture conductivity.
