Relationship Between the 2-acrylamido-2-methylpropane Sulfonic Acid–NNDMA Copolymer Properties and Fluid Loss and Mixability in Cementing Fluids

Five different variants of the acrylamidotertiary-butyl sulfonic acid (ATBS) / N,N-dimethylacrylamide (NNDMA) copolymer were examined and evaluated, comparing their mixability and fluid-loss performance. These were characterized using gel permeation chromatography equipped with multi-angle laser light scattering (GPC-MALLS) and viscometry to evaluate the effects of number average molecular weight (Mn), radius of gyration (Rg), dispersity (Đ), and viscosity values in water and cement. It was determined that there was an optimum Đ value at which the mixability performance of the cement slurry formulated with the fluid loss copolymer was achieved. Additionally, it was determined that an increase in Đ improved fluid loss performance for a given Mn and Rg. More interestingly, an increase in Rg at fixed Mn and Đ decreases fluid-loss performance, which is counterintuitive to the particle bridging mechanism. A quantitative relationship between the copolymer characteristics and its fluid-loss performance was determined. Understanding the relationship between structure and function of 2-acrylamido-2-methylpropane sulfonic acid-NNDMA copolymers in a cement slurry is the first step toward designing fluid-loss additives with targeted properties.