Synthesis Of Block Copolymer Fracturing Fluid Thickeners By Active Free Radical Polymerization

In this thesis, a novel kind of hydraulic fracturing fluid system which shows good performance and industry application potentials was developed. The system mainly contains a water-soluble block copolymer thickening agent, which is prepared by controllable radical polymerization. Radical density and the polymerization degree in this polymerization are controlled by the reversible addition fragmentation transfer(RAFT) dual function dithioester initiator. Starting from styrene (St), methacrylic acid (MAA) and ethyl acrylate (EtA) as the main monomers, diblock copolymer and triblock copolymer with one water-soluble block and one hydrophobic block were obtained via the emulsion polymerization method. Satisfactory fracturing fluid thickening agent was yielded by further hydrolysis of the copolymers. For the diblock copolymer, its inherent viscosity was determined by viscometric method.Experimental results proved that the polymerization underwent a living radical polymerization process. Factors which influence the polymerization, including the monomer molar ratio, the amount of sodium hydroxide, the time of hydrolysis and the amount of dithioester, were investigated in terms of the viscosity of polymer thickening agent. The optimized polymerization conditions are as follows: the molar ratio of EtA/St is 9.6, the molar ratio of NaOH/EtA is 0.66, weight percentage of dithioester is 0.75% and the time for hydrolysis step is 12 h. In addition, the performance of the diblock copolymer fracturing fluid system is measured and this system shows satisfactory properties, including anti-salt property, shear performance, temperature resistance, rheological and gel-breaking performance. At concentration of 4%, the polymer fracturing fluid exhibited excellent high-temperature stability up to 165℃. It can be used in deep well fracturing operation even to a high temperature(210℃) at concentration of 5%. In the similar manner to diblock copolymer system, triblock copolymer fracturing fluid system was prepared and its performance was evaluated. The results show that the triblock fracturing fluid system has good temperature resistance, gel-breaking and rheological performance. The viscosity for a 4wt% triblock copolymer fracturing fluids is above 270 mPa·s at 90℃.