Investigation of cellulose nanofiber enhanced viscoelastic fracturing fluid system: Increasing viscoelasticity and reducing filtration

Synthesis and Characterization of a Resin/Acrylamide-2-acrylamide-2-methylpropane Sulfonate-Diallyl Dimethyl Ammonium Chloride-N-vinyl-2-pyrrolidinone Polymer Microcapsule Gelling Agent for Oil and Gas Field Transformation

Deep carbonate rock oil and gas reservoir is an important support for increasing oil and gas storage and production at present. The environment of ultradeep and ultrahigh-temperature reservoirs has put forward higher technical requirements for reservoir modification acid technology. Moreover, gelling acid is the main acid solution for high-temperature reservoir acidizing transformation, with a temperature resistance of no more than 180 °C, and the gelling agent is one of the key factors restricting its high-temperature resistance performance. In this paper, AM, AMPS, DMDAAC, and NVP were used as monomers, oxidants, and reducing agents to prepare a high-temperature-resistant polymer gel through polymerization. At the same time, microcapsules were prepared by in situ polymerization using epoxy resin as the wall material. The indoor performance evaluation results indicate that the gelling agent is easily soluble in high-concentration acid solution and has good viscosity increasing effect. At 180 °C and 170 s-1 shear rate, 0.8% mass fraction of the gelling agent was dissolved in 20% mass fraction of hydrochloric acid. After shearing for 60 min, the viscosity remained at about 22.45 mPa·s, demonstrating good temperature resistance and shear resistance, and its performance was superior to existing commonly used gelling agent products.

Experimental Study on the Stability of a Novel Nanocomposite-Enhanced Viscoelastic Surfactant Solution as a Fracturing Fluid under Unconventional Reservoir Stimulation

Fe3O4@ZnO nanocomposites (NCs) were synthesized to improve the stability of the wormlike micelle (WLM) network structure of viscoelastic surfactant (VES) fracturing fluid and were characterized by Fourier transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). Then, an NC-enhanced viscoelastic surfactant solution as a fracturing fluid (NC-VES) was prepared, and its properties, including settlement stability, interactions between NCs and WLMs, proppant-transporting performance and gel-breaking properties, were systematically studied. More importantly, the influences of the NC concentration, shear rate, temperature and pH level on the stability of NC-VES were systematically investigated. The experimental results show that the NC-VES with a suitable content of NCs (0.1 wt.%) shows superior stability at 95 °C or at a high shear rate. Meanwhile, the NC-VES has an acceptable wide pH stability range of 6-9. In addition, the NC-VES possesses good sand-carrying performance and gel-breaking properties, while the NCs can be easily separated and recycled by applying a magnetic field. The temperature-resistant, stable and environmentally friendly fracturing fluid opens an opportunity for the future hydraulic fracturing of unconventional reservoirs.

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.