2.2 Evaluation of Retarder Performance

(1) Thickening performance

The changes in cement slurry thickening were tested at temperatures of 60℃, 90℃, 120℃, and 150℃, respectively. The experimental results are shown in Figure 5. From Figure 5, it can be seen that as the thickening temperature increases, the thickening time of the cement slurry decreases. The thickening times at temperatures of 60℃, 90℃, 120℃, and 150℃ are 427min, 337min, 275min, and 235min, respectively. The thickening curve is stable, without any sudden changes in viscosity, and the transition time is short. The thickening curve has obvious right angle characteristics, indicating that the retarder PADBrC has good adaptability to large temperature differences and can meet the needs of 60-150℃ cementing construction.

(2)Compressive Strength

The compressive strength of cement stone after 24 hours of curing with cement slurry under different PADBrC dosages and temperature conditions is shown in Table 2. According to Table 2, as the curing temperature increases, the compressive strength of cement stone increases. Comparing the compressive strength of cement stone at the same temperature, it can be seen that as the amount of PADBrC increases, the compressive strength of cement stone decreases. At 120℃, the compressive strength of cement stone is greater than 25MPa, while at 60℃, the compressive strength of cement stone can still reach 14.8MPa, which is greater than the 14.0MPa required for construction. This indicates that the addition of retarder PADBrC has a relatively small impact on the compressive strength of cement stone under large temperature difference conditions.

2.3 Analysis of Retardation Mechanism

(1)XRD analysis

The hydration products of cement paste cured with PADBrC were tested and analyzed using an X-ray diffractometer, and compared with blank cement paste samples. The test results under the conditions of curing temperature of 60℃, 120℃, and curing time of 24 hours are shown in Figure 6. It can be seen from Figure 6 that the hydration products of the cement paste added with PADBrC and the blank cement paste are basically the same. The diffraction peaks of calcium hydroxide (Ca (OH) ₂), ettringite (AFt) and calcium silicate hydrate gel (C-S-H) appear in the hydration products, indicating that the addition of PADBrC has little effect on the generation of cement hydration products. However, the addition of PADBrC resulted in a change in the diffraction peak intensity of different hydration products. From Figure 6, it can be seen that the diffraction peak intensity of Ca (OH) ₂ and C-S-H in the hydration products of water debris at 60℃ has significantly decreased, while the hydration rate of cement has significantly accelerated after the temperature rises to 120℃. However, the addition of PADBrC also significantly reduces the diffraction peak intensity of Ca (OH) ₂ and C-S-H in the hydration products of cement paste, indicating that the addition of PADBrC can inhibit the generation of Ca (OH) ₂ and C-S-H in the cement slurry under large temperature difference conditions, thereby prolonging the cement hydration time.

(2)SEM analysis

Perform scanning electron microscopy analysis on blank cement paste and cement paste with added PADBrC. From Figure 7, it can be seen that there is a significant difference in the cross-sectional microstructure between the cement paste without added PADBrC (Figures 7a-b) and the cement paste with added PADBrC (Figures 7c-d). Many thin layered Ca (OH) ₂ crystals, needle cluster like C-S-H, and a small amount of needle columnar AFt crystals can be seen in the blank cement stone; After adding PADBrC, the amount of sheet-like Ca (OH) ₂ crystals in cement paste significantly decreased, and the C-S-H and AFt crystals also decreased accordingly. Most of the areas were amorphous substances, indicating that the addition of PADBrC inhibited the generation of hydration products such as Ca (OH) ₂ crystals and C-S-H, and to some extent delayed the hydration of cement. And this phenomenon is mainly due to the presence of - SO₃H, - COOH, and quaternary ammonium salt ions in PADBrC. On the one hand, these functional groups selectively adsorb on the surface of cement particles, forming a protective film that shields the contact between cement particles and water, thereby delaying cement hydration; On the other hand, the - COOH in PADBrC molecules has a strong chelating ability towards Ca²⁺. After PADBrC molecules are added to the cement slurry, the Ca²⁺in the cement slurry complexes with the - COOH in PADBrC, resulting in a decrease in Ca²⁺concentration in the cement slurry system. However, a large amount of complex precipitates adsorb onto the growing Ca (OH) ₂ crystals, hindering the precipitation of Ca (OH) ₂ crystals and the development of hydration product nuclei, thereby prolonging the induction period and reducing the hydration rate of cement paste.

3.Conclusion

This article synthesized a large temperature difference retarder PADBrC for oil well cement by using 2-methyl-2-acrylamidopropane sulfonic acid (AMPS), acrylic acid (AA), methacryloxyethyl trimethylammonium chloride (DMC), and long-chain quaternary ammonium salt (DBrC) as monomers and using aqueous solution free radical polymerization method. The research results show that PADBrC has a significant retarding effect and can effectively prolong the thickening time of cement slurry within the temperature difference range of 60-150℃, with a stable thickening curve; When the dosage of PADBrC is 0.6%, 0.8%, and 1.0%, the compressive strength of cement paste cured at 120℃ for 24 hours is greater than 25MPa. Even at 60℃, the compressive strength of cement paste can still be greater than 14MPa. The hydration products of cement were analyzed by X-ray diffraction and scanning electron microscopy, and the results showed that the addition of PADBrC to cement paste suppresses the generation of Ca (OH) ₂ and C-S-H in the cement, thereby suppressing the hydration effect of cement.

Our company has developed and produced a series of high temperature oil well cementing retarder products, among which ZOC-R32S and ZOC-H42L have similar performance to the PADBrC mentioned in this article. Specific product information can be browsed and queried on our website www.zoranoc.com. Please feel free to inquire.