Turbulent Drag Reduction with an Ultra-High-Molecular-Weight Water-Soluble Polymer in Slick-Water Hydrofracking

Abstract

Water-soluble polymers as drag reducers have been widely utilized in slick-water for fracturing shale oil and gas reservoirs. However, the low viscosity characteristics, high operating costs, and freshwater consumption of conventional friction reducers limit their practical use in deeper oil and gas reservoirs. Therefore, a high viscosity water-soluble friction reducer (HVFR), poly-(acrylamide-co-acrylic acid-co-2-acrylamido-2-methylpropanesulphonic acid), was synthesized via free radical polymerization in aqueous solution. The molecular weight, solubility, rheological behavior, and drag reduction performance of HVFR were thoroughly investigated. The results showed that the viscosity-average molecular weight of HVFR is 23.2 × 10⁶ g⋅mol^-1. The HVFR powder could be quickly dissolved in water within 240 s under 700 rpm. The storage modulus (G') and loss modulus (G″) as well as viscosity of the solutions increased with an increase in polymer concentration. At a concentration of 1700 mg⋅L^-1, HVFR solution shows 67% viscosity retention rate after heating from 30 to 90 °C, and the viscosity retention rate of HVFR solution when increasing C_NaCl to 21,000 mg⋅L^-1 is 66%. HVFR exhibits significant drag reduction performance for both low viscosity and high viscosity. A maximum drag reduction of 80.2% is attained from HVFR at 400 mg⋅L^-1 with 5.0 mPa⋅s, and drag reduction of HVFR is 75.1% at 1700 mg⋅L^-1 with 30.2 mPa⋅s. These findings not only indicate the prospective use of HVFR in slick-water hydrofracking, but also shed light on the design of novel friction reducers utilized in the oil and gas industry.

Keywords: drag reducer; hydrofracking; rheological behavior; slick-water; water-soluble polymer.

Figure 1

Comparison of the FTIR spectra of copolymer HVFR versus monomers AM and AMPS.

Figure 2

¹H NMR spectrum of HVFR dissolved in D₂O.

Figure 3

η_sp/C_p and (lnη_r/C_p) plotted against polymer concentration for HVFR in 1 M NaCl solution at 30 °C.

Figure 4

Determination of dissolution time of 1000 mg⋅L⁻¹ HVFR at 30 °C.

Figure 5

Shear viscosity plotted as a function of shear rate for HVFR solutions with different concentrations at 30 °C.

Figure 6

(A) Effect of temperature on apparent viscosity for HVFR solutions with different concentrations; (B) Logarithmic plots of viscosity against the reciprocal of temperature for HVFR.

Figure 7

Variation of the apparent viscosity versus NaCl concentration for 1700 mg⋅L⁻¹ HVFR at 30 °C.

Figure 8

The storage and loss modulus plotted as a function of (A) strain and (B) frequency for HVFR solution at 30 °C.

Figure 9

The dependence of drag reduction and apparent viscosity on polymer concentration (T, 30 °C; shear rate, 170 s⁻¹; flux, 170 L⋅min⁻¹).

Figure 10

Comparison of the drag reduction versus flux for HVFR at 500 and 1700 mg⋅L⁻¹ at 30 °C.

Scheme 1

Schematic route toward the preparation of HVFR.