Preparation and Application of a Salt- and Shear-Resistant Thickening Agent

Conventional salt-resistant thickening agents cannot satisfy the requirement of recycling gas-field waters because of their limited salt resistance and poor high-speed shearing resistance. In this study a polymer thickening agent ASCM was developed to deal with this problem. ASCM is synthesized by emulsion polymerization with these monomers: acrylamide (AM), sodium p-styrenesulfonate (SSS), N,N-diethylacrylamide (DEAM), alkyldimethylally ammonium chloride (CnDMAAC). The synthesis conditions were optimized through orthogonal experiments. ASCM has salt tolerance of 85 000 mg/L and Ca²⁺ and Mg²⁺ tolerance of 6 000 mg/L. In standard salt water ASCM has viscosity retention rate of about 80%. After shearing at 2 000 s⁻¹, 90% of the viscosity can be restored. A 1.6%ASCM solution formulated with a gas field water had viscosity of about 50 mPa·s after shearing at 120℃ and 170 s⁻¹ for 90 min. After statically suspending for 2 h, no settlement of sand was found. The gel of the ASCM solution can be broken under control in 30-120 min. The solution after gel breaking had surface tension of 25-27 mN/m, residue content of less than 200 mg/L, and core damage of less than 25%. ASCM fracturing fluid formulated with gas field waters and flowback liquids was used for 9 well times, the accumulated volume of the reused gas field waters and flowback liquids reached 1.43 × 10⁴ m³, the operation parameters and stimulation effects of the fracturing fluid formulated with ASCM were the same with those of the fracturing fluids formulated with fresh water, and the comprehensive cost was saved by more than 20%. ASCM has the characteristics of good shear resistance, high suspending capacity, low formation damage and low friction, satisfying the needs of large-scale reuse of waters with complex water quality, such as gas field waters and flowback fluids.