Modulation of the Viscosity of Guar-Based Fracking Fluids Using Salts

Abstract

Fracking is an enhanced oil recovery technology, which uses viscoelastic fluids (fracking fluids) to fracture oil reservoirs and to transport sand within the fractures, to prop them open. This technology enables oil recovery from scarcely permeable formations. Fractured formations release saline water over time. This saline water (called “produced water”) is discarded rather than used to produce fracking fluids because it can decrease fracking fluid viscosity. Nonetheless, it would be advantageous to use produced water to reduce freshwater consumption and wastewater production. Our study analyzes the effect of chloride salts (CaCl2, MgCl2, and Fe­(III)­Cl) and of sulfate salts (MgSO4 and FeSO4) at different concentrations (0.05–1 M) on the viscosity of aqueous guar solutions. All chloride salts tested increase the viscosity of guar solutions in the concentration range analyzed and promote the formation of small guar aggregates. At 0.05 M concentrations, MgSO4 has effects similar to chloride salts. In contrast, 1 M MgSO4 decreases the viscosity of guar solutions. FeSO4 also decreases the viscosity of aqueous guar solutions, at either 0.05 or 1 M concentrations. The decrease in viscosity of guar solutions is attributed to large guar aggregate formation (as opposed to a cohesive network). Sodium cocoyl glutamate (SCG) increases the viscosity of non-cross-linked guar solutions and the shear viscoelastic moduli of guar solutions cross-linked with sodium tetraborate. Specifically, SCG restores the viscosity of guar solutions with MgSO4 and increases it above values measured in deionized (DI) water in the presence of MgCl2. Attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy shows that hydrogen bonding was more significant in guar + SCG + 0.7 M MgCl2 samples than in guar + SCG + 0.7 M MgSO4, indicating that the formation of a hydrogen-bonded network was correlated to high viscosity. ATR-FTIR also indicates that MgSO4 weakened hydrogen bonding of water clusters, whereas SCG restored it, enabling guar hydration even in the presence of MgSO4. Our study highlights which salts are most problematic (e.g., FeSO4) and proposes a potential additive (SCG) to enhance the viscosity of guar in the presence of selected salts (e.g., magnesium salts) by promoting hydrogen bonding.

Review on High-Temperature-Resistant Viscoelastic Surfactant Fracturing Fluids: State-of-the-Art and Perspectives

“…Two or more identical or different thickener materials (biopolymer/surfactant, − synthetic polymer/surfactant, ,,, surfactant/surfactant, ,− etc.) are mixed according to a certain proportion.…”

Investigation on the influence of sulfonic substitution in polyacrylamides for minimizing drag in turbulent flow of slickwater fluids

“…[1][2][3] Fracturing in conventional reservoirs, fluids were developed by guarbased aqueous systems and these fluids have been designated as linear gels, possessing a substantial viscosity and the ability to transport proppants. 4,5 Linear gels were enhanced by crosslinkers stabilized for high-temperature and high-salinity conditions and were termed as crosslinked gels. [6][7][8][9] Techniques were modified for lowpermeability unconventional wells where fluids consisting of drag-reducing polymers in produced waters, termed as slickwater fluids, were pumped at highflowrates to achieve turbulent conditions for proppant suspension 10,11 to mitigate frictional losses.…”

Preparation and evaluation of acryloyl morpholine modified emulsion fracturing fluid thickener with high temperature resistance and salt resistance

“…Guar gum fracturing fluid has the advantages of strong sand carrying ability, salt resistance, easy crosslinking, low filtration loss, so guar gum fracturing fluid has always been the first choice for oilfield fracturing 11,12 . However, the temperature resistance of guar gum fracturing fluid is weak, and it is generally lower than 180°C.…”

“…9,10 Guar gum fracturing fluid has the advantages of strong sand carrying ability, salt resistance, easy crosslinking, low filtration loss, so guar gum fracturing fluid has always been the first choice for oilfield fracturing. 11,12 However, the temperature resistance of guar gum fracturing fluid is weak, and it is generally lower than 180 C. To make the temperature resistance exceed 180 C, the amount of guar gum is generally higher than 0.60%, and the excessive guar gum concentration leads to the increase of fracturing fluid viscosity, construction pump pressure, and the residue content of gum breaking fluid. 13,14 Compared with gum fracturing fluid, polymer fracturing fluid has excellent temperature resistance and drag reduction performance, and less damage to the reservoir.…”