Synthesis and application of a novel betaine-type copolymer as fluid loss additive for water-based drilling fluid

The zwitterionic copolymers are widely used for fluid loss additive in water-based drilling fluid due to their good performance in reducing the filtration loss and inhibiting the swelling of shales. However, there are still shortcomings to the conventional zwitterionic copolymer such as the poor properties of salt tolerance and thermal stability. This study synthesized a new kind of copolymer consisting of acrylamide (AM), 2-acryloylamino-2-methyl-1-propanesulfonic acid (AMPS), diallyl dimethyl ammonium chloride (DMDAAC), and the synthesized betaine-type monomer (vinylphenyl sulfonate (VPS)) (copolymer (PVAAD)) through introducing AMPS, DMDAAC, and VPS onto the backbone of AM via the method of free radical polymerization in aqueous solution. The biggest difference of PVAAD with the conventional zwitterionic copolymer is that there are zwitterions in the same chain and the different chain in the molecular structure of PVAAD. Results of performance evaluation show that the synthesized PVAAD used as fluid loss additive has good performances. It could be used as a fluid loss additive for water-based drilling fluid in salty and high-temperature environment. After adding 1.25 wt% of PVAAD, the structure of the filter cake of the copolymer drilling fluid system becomes relatively uniform and dense, and the particle size distribution of the freshwater drilling fluid tends to become more rational. Compared with the other commercial fluid loss additives, the synthesized PVAAD has a better property of high-temperature resistance and performance in controlling the American Petroleum Institute (API) filtration loss of drilling fluid systems.