Untreatment reutilization of high-salinity flowback fluid and produced water to prepare fracturing fluid by using associative thickener

Reutilizing flowback fluid and produced water to prepare fracturing fluid is still an urgent problem that needs to be solved and is not well solved. In this work, an anti-salt associative thickener (AAT) was synthesized by free radical copolymerization, and the molecular structure of AAT was demonstrated by FTIR and ¹H-NMR. Furthermore, compared with a common anti-salt thickener (HAT), the comprehensive performances of AAT were systematically investigated under the conditions of fresh water, flowback fluid and produced water in Sulige Gasfield. The results show that under the conditions of an average salinity of 34,428 mg/L and an average high-valent ion content of 4967 mg/L, AAT can present good thickening capacity, temperature and shear resistance, drag reduction efficiency, sand-carrying ability, gel-breaking property and high-effective crosslinking capacity with organic zirconium crosslinker at high salinity, which implicates the great potential and feasibility to prepare fracturing fluid by reutilizing high-salinity flowback fluid and produced water without further treatment. Moreover, the possible mechanisms of the associative thickener to achieve high-effective drag reduction and sand-carrying might be the existence of reversible supramolecular structures and the significant increase of viscoelasticity by shear stretching in turbulent state. At the same time, both physical and chemical interaction can make a significant contribution to high-effective crosslinking capacity of associative thickener. All results and findings can provide an important reference for the design of novel fracturing fluid and the reutilization of high-salinity water in stimulation applications.