Gemini Surfactant with Unsaturated Long Tails for Viscoelastic Surfactant (VES) Fracturing Fluid Used in Tight Reservoirs

Synthesis and Properties of Exceptionally Thermo-Switchable Viscoelastic Responsive Zwitterionic Gemini Surfactants in Highly Saline Water

Viscoelastic surfactants (VESs) have significant importance for stimulation of low-permeable reservoirs and acid diversion applications to effectively enhance hydrocarbon productivity. VESs offer lower residues, complete gel production, and lower formation damage that make them suitable candidates for hydraulic fracturing applications. In this research work, the synthesis of two new zwitterionic gemini surfactants 1 and 2 together with previously known amidosulfobutaine (C₁₈AMP3SB) has been achieved. Evaluation of viscosity behavior of neat surfactants in CaCl₂ solutions at varied temperatures and shear rates did not show any upsurge in their viscosities. Nevertheless, a mixture of surfactants 1 and 2 in combination with C₁₈AMP3SB displayed a significant increase in viscosity, transforming the solution into a highly viscous gel. At a fixed shear rate of 35 s^-1 and under different temperatures, solutions of the mixture of surfactants 1 and C₁₈AMP3SB displayed viscosities ranging from 4.34 to 354.3 cPs (81-fold enhancement). Likewise, viscosities of formulations based on mixing 2 and C₁₈AMP3SB under identical experimental conditions ranged from 3.89 to 290 cPs (74-fold enhancement). The viscofying stability tests at 90 °C at a shear rate of 35 s^-1 of mixed surfactant formulations revealed no appreciable change in their viscosities for up to 1 h. Moreover, temperature-dependent experiments suggested an increase in the viscosity with an increase in temperature. Thermogravimetric analysis revealed that these surfactants are thermally stable, with no appreciable loss of mass up to 300 °C. The viscoelastic properties of these surfactants suggest their potential and utility in well stimulation for enhanced oil recovery.

Novel Trends in the Development of Surfactant-Based Hydraulic Fracturing Fluids: A Review

Viscoelastic surfactants (VES) are amphiphilic molecules which self-assemble into long polymer-like aggregates-wormlike micelles. Such micellar chains form an entangled network, imparting high viscosity and viscoelasticity to aqueous solutions. VES are currently attracting great attention as the main components of clean hydraulic fracturing fluids used for enhanced oil recovery (EOR). Fracturing fluids consist of proppant particles suspended in a viscoelastic medium. They are pumped into a wellbore under high pressure to create fractures, through which the oil can flow into the well. Polymer gels have been used most often for fracturing operations; however, VES solutions are advantageous as they usually require no breakers other than reservoir hydrocarbons to be cleaned from the well. Many attempts have recently been made to improve the viscoelastic properties, temperature, and salt resistance of VES fluids to make them a cost-effective alternative to polymer gels. This review aims at describing the novel concepts and advancements in the fundamental science of VES-based fracturing fluids reported in the last few years, which have not yet been widely industrially implemented, but are significant for prospective future applications. Recent achievements, reviewed in this paper, include the use of oligomeric surfactants, surfactant mixtures, hybrid nanoparticle/VES, or polymer/VES fluids. The advantages and limitations of the different VES fluids are discussed. The fundamental reasons for the different ways of improvement of VES performance for fracturing are described.