Preparation and Properties of a Novel Multi-Functional Viscous Friction Reducer Suspension for Fracturing in Unconventional Reservoirs

Abstract

Aiming at the problem that conventional friction reducers used in fracturing cannot simultaneously possess properties such as temperature resistance, salt resistance, shear resistance, rapid dissolution, and low damage. Under the design concept of "medium-low molecular weight, salt-resistant functional monomer, supramolecular physical crosslinking aggregation, and enhanced chain mechanical strength", acrylamide, sulfonic acid salt-resistant monomer 2-acrylamide-2-methylpropanesulfonic acid, hydrophobic association monomer, and rigid skeleton functional monomer acryloyl morpholine were introduced into the friction reducer molecular chain by free radical polymerization, and combined with the compound suspension technology to develop a new type of multi-functional viscous friction reducer suspension (SAMD), the comprehensive performance of SAMD was investigated. The results indicated that the critical micelle concentration of SAMD was 0.33 wt%, SAMD could be dissolved in 80,000 mg/L brine within 3.0 min, and the viscosity loss of 0.5 wt% SAMD solution was 24.1% after 10 min of dissolution in 80,000 mg/L brine compared with that in deionized water, the drag reduction rate of 0.1 wt% SAMD solution could exceed 70% at 120 °C and still maintained good drag reduction performance in brine with a salinity of 100,000 mg/L. After three cycles of 170 s^-1 and 1022 s^-1 variable shear, the SAMD solution restored viscosity quickly and exhibited good shear resistance. The Tan δ (a parameter characterizing the viscoelasticity of the system) of 1.0 wt% SAMD solution was 0.52, which showed a good sand-carrying capacity, and the proppant settling velocity in it could be as low as 0.147 mm/s at 120 °C, achieving the function of high drag reduction at low concentrations and strong sand transportation at high concentrations. The viscosity of 1.4 wt% SAMD was 95.5 mPa s after shearing for 120 min at 140 °C and at 170 s^-1. After breaking a gel, the SAMD solution system had a core permeability harm rate of less than 15%, while the SAMD solution also possessed the performance of enhancing oil recovery. Compared with common friction reducers, SAMD simultaneously possessed the properties of temperature resistance, salt resistance, shear resistance, rapid dissolution, low damage, and enhanced oil recovery. Therefore, the use of this multi-effect friction reducer is suitable for the development of unconventional oil reservoirs with a temperature lower than 140 °C and a salinity of less than 100,000 mg/L.

Keywords: friction reducer; high salinity; high temperature; low damage; shear resistance.

Figure 1

FTIR spectra of AMD.

Figure 2

Apparent viscosity of AMD solutions with different mass fractions.

Figure 3

The viscosity–time plots of SAMD and SPAM.

Figure 4

Variation in the viscosity of SAMD solutions as a function of inorganic salt concentrations.

Figure 5

Curves of drag reduction rate with velocity under different conditions. (A) SAMD concentrations, (B) salinities, and (C) temperatures.

Figure 6

Viscosity curves of 1.0 wt% SAMD solution at different shear rates.

Figure 7

The viscoelasticity of SAMD. (A) Strain scanning curve and (B) frequency scanning curve.

Figure 8

SEM images of SAMD solutions with different mass fractions: (A) 0.10 wt%, (B) 0.30 wt%, (C) 0.60 wt%, and (D) 1.0 wt%. The magnification of the Figure 8 is 2000×.

Figure 8

SEM images of SAMD solutions with different mass fractions: (A) 0.10 wt%, (B) 0.30 wt%, (C) 0.60 wt%, and (D) 1.0 wt%. The magnification of the Figure 8 is 2000×.

Figure 9

Temperature and shear resistance curves of SAMD solution at different temperatures: (A) 1.0 wt% SAMD at 120 °C and (B) 1.4 wt% SAMD at 140 °C.

Figure 9

Temperature and shear resistance curves of SAMD solution at different temperatures: (A) 1.0 wt% SAMD at 120 °C and (B) 1.4 wt% SAMD at 140 °C.

Figure 10

Effect of different gel-breaking fluids on harm rate of core displacement: (A) 0.3 wt% SAMD, (B) 0.5 wt% SAMD, (C) 0.5 wt% SAMD + 0.1 wt% microemulsion cleanup additive, and (D) permeability change.

Figure 11

The imbibition recovery of different solutions.

Figure 12

Synthetic equation of AMD.