Performance Enhancements of Viscoelastic Surfactant Stimulation Fluids With Nanoparticles

Abstract

Abstract High-molecular-weight crosslinked polymer fluids have been used to stimulate oil and gas wells for decades. These fluids exhibit exceptional viscosity, thermal stability, proppant transportability, and fluid leak-off control. However, a major drawback of crosslinked polymer fluids is the amount of polymer residue they leave behind. Polymer residue has been shown to significantly damage formation permeability and fracture conductivity. 1–3 Recently, viscoelastic surfactant (VES) fluids composed of low-molecular-weight surfactants have been used as hydraulic fracturing and frac-packing fluids. The surfactants structurally arrange in brine to form rod-like micelles that exhibit viscoelastic fluid behavior. VES fluids, once broken, leave very little residue or production damage. However, excessive fluid leak-off and poor thermal stability has significantly limited their use. This paper will introduce newly developed, select nano-size crystals with unique surface charges and will explain how nanoparticle technology pseudo-crosslinks VES rod-like micelles together to improve the fluid loss control and proppant transport of VES fluids to a performance level similar to that of crosslinked polymer fluid. The nanoparticle pseudocrosslinked VES micelle fluid develops a wall-building pseudo-filtercake on the face of porous media to control fluid loss. When internal breakers are used to degrade the VES micelle structures the leaked-off VES fluid and the pseudo-filtercake breaks into brine water and nanoparticles. Since the nanoparticles are very small and readily pass through the pores of greater than 0.1 md formations, they are flowed back with the produced fluids, and no internal or external "solids" damage is generated. This paper will present laboratory data that shows how uniquely charged nanoparticles improve VES fluid rheology, leak-off control, and proppant suspension. Also presented are test results comparing nanoparticle enhanced VES to borate crosslinked guar polymer fluids. The mechanisms that enhance the performance of these fluids also will be discussed. Introduction Crosslinked polymer fluids (CPF) are the most common type of fluid used for hydraulic fracturing. These fluids can achieve high viscosities with low leak-off rates for a wide range of reservoir temperatures and permeabilities. With their efficient leak-off control, CPF can be used to generate excellent fracture geometry in most reservoirs. They also have excellent proppant suspension and placement capability. However, CPF have an inherent weakness that decades of developing internal breaker technologies have not been able to resolve: this weakness is the amount of fracture conductivity damage that occurs due to incomplete crosslinked-polymer filtercake removal from the fracture. A recent Joint Industry Project study has showed that polymeric filtercake thickness, and its yield stress, is one of the primary culprits to poor fracture cleanup and fracture conductivity loss when using crosslinked polymer fluids. 4