Effects of the Molecular Structure of Block Polymer Developed through RAFT Polymerization on Filtration Property of Drilling Fluids

A series of isomeric zwitterionic filter loss reducers have been developed for investigating the effects of the molecular structure of polymers on their filtration control performance. These isomeric zwitterionic filter loss reducers were synthesized through reversible addition-fragmentation chain transfer polymerization (RAFT) with monomers such as AMPS (ionic monomer), 1-vinyl-3-ethylimidazollium bromide (VeiBr, as cationic monomer) and acrylamide (AM, as neutral monomer). By adjusting the sequence of adding different monomers, three copolymers, which are a random copolymer, a partial block polymer and a full block copolymer, respectively. These three copolymers have precise molecular structures, different bonding sequence (of atoms) and narrowly distributed and controllable molecular weights. Laboratory performance evaluation of these copolymers have shown that under the same test conditions, the random copolymer has the best filtration control performance, while the block copolymers can be used to make high YP/PV ratio flow pattern modifiers. By changing the concentration of the chain transfer agent, the molecular weight of the copolymers can be effectively adjusted, and this helps analyze the effects of copolymers with the same molecular structure and different molecular weights. It was found that the higher the molecular weight, the higher the viscosity and the better the filtration control performance of the copolymers. It is thus concluded that block polymers with random sequence structure are more suitable for filtration control in drilling fluids, and polymers with higher molecular weight will perform better in this aspect. This study has provided a theoretical base for developing high efficiency molecular structure oriented filter loss reducers.