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.

A Novel Branched Polymer Gel System with Delayed Gelation Property for Conformance Control

Summary Excessive water production from oil reservoirs not only affects the economical production of oil, but it also results in serious environmental concerns. Polymer gels have been widely applied to decrease water production and thus improve oil production. However, traditional polymer gels such as partially hydrolyzed polyacrylamide (HPAM)/chromium (III) gel systems usually have a short gelation time and cannot meet the requirement of some conformance control projects. This paper introduces a novel polymer gel system of which crosslinking time can be significantly delayed. A branched polymer grafted from arginine by the surface initiation method is synthesized as the backbone, chromium acetate is used as the crosslinker, and no additional additives are used for the gel system. The results show that the gelation time of this system can be delayed to 61 days at 45°C and 20 days at 65°C because of the rigid structure of the branched polymer and the excellent chromium (III) chelating ability of arginine. The polymer gels have been stable for more than 150 days at 45 and 65°C. Coreflooding and rheology tests have demonstrated that this branched polymer has good injectivity and shear resistance in high-permeabilityrocks.

Synthesis of Allyl Pentaerythritol Crosslinker based Polymer Hydrogels and Determination of the Crosslink Density

In this study, we report the synthesis and characterization of polymer hydrogels. The polymer gels have been prepared from acrylic acid (AA) monomer using allyl pentaerythritol as the crosslinker in the presence of potassium persulfate initiator. The synthesized polymer gels have been characterized by Fourier-transform infrared (FT-IR) spectroscopy. The swelling capacity and crosslink density of the synthesized polymer gels have been determined and it was found that some of the polymer samples behave like super-absorbent polymers. These polymeric-gels can be utilized in various applications viz. as a catalyst for dye removal, for anion removal from water and for heavy metal removal etc.