A Novel Hydrophobic Associative Polymer by RAFT-MADIX Copolymerization for Fracturing Fluids with High Thermal Stability

Hydrophobic associative water-soluble polymers (HAWSP) are widely used as thickening agents for fracturing fluids due to their excellent viscoelastic properties. However, the HAWSP products synthesized by conventional methods are generally poor in resisting higher temperatures. In order to solve this problem, the effects of molecular weight and amount of hydrophobic monomer on the rheological properties of hydrophobic were investigated carefully. The macromolecular chain transfer agent was prepared through the process of reversible addition–fragmentation chain transfer polymerization (RAFT)/macromolecular designed by the interchange of xanthates (MADIX), and then the terpolymer of AM-co-AA-co-N-(3-methacrylamidopropyl)-N,N-dimethyldodecan-1-aminium (MAO-12DMA) was synthesized. The polymer has a narrow molecular-weight distribution giving rise to a good solubility even when the molecular-weight and the content of hydrophobic monomer are relatively high. Our study shows that the increase of molecular-weight was beneficial to improve resistance to higher temperatures. The increase of hydrophobic monomer content had a positive effect on improving the rheological properties at low temperature, but had no obvious influence on rheological properties at high temperature. Based on this principle, a novel HAWSP fracturing fluid thickener, which can resist high temperatures of 160 °C, was obtained. The new thickener has a lower initial viscosity than traditional HAWSP and has better stability at high temperatures. This overcomes the shortcomings of increasing the dosage and initial viscosity as a strategy for increasing resistance to high temperatures, which leads to pumping difficulties. In addition, with other advantages like good shear-resistance, clean and easy preparation, the fracturing fluid described here will be very useful and practical for final application in oilfields.