Preparation of hydrophobic associative copolymer and its application performance evaluation for oil well cement slurry

Abstract To address the challenges in high-temperature and ultra-high-temperature cement slurry (CS), where the performance of CS is difficult to control because of the inevitable group variation and thermal degradation of copolymer additives, this study introduces hydrophobic associative (HA) monomer into the molecular structure of copolymeric fluid loss additives to form HA copolymers. This approach is aimed at enhancing the high-temperature suspension and fluid loss control properties of CS. The effect of HA monomers with varying concentrations on the HA properties of copolymers is also compared and examined. The research findings indicate that copolymers with long alkyl hydrophobic side chains, specifically the quaternary ammonium salt organic cation structure of octadecyl dimethyl allyl chloride ammonium, exhibit strong HA characteristics. At a low dosage (0.6 wt% bwoc) of HA copolymer, the API fluid loss volume of the CS after curing at 240°C for 9 h is less than 50 mL/30 min, and it can mitigate the deterioration of rheological properties and maintain high-temperature stability of the CS. Furthermore, the conventional density ultra-high-temperature CS, using prepared HA copolymer as a key additive, demonstrates low fluid loss, good flowability, strong slurry stability, easily adjustable thickening time, and good thickening stability, as well as rapid development of early compressive strength at ultra-high-temperature conditions of 210/240°C, which meets the cementing technical requirements for deep/ultra-deep wells.