It can be seen that the effective transition time of cement slurry can be adjusted from 1 ℃ to 70 ℃. It can be seen from Fig. 2 that at 120-200 ℃, at the same dosage of ZOC-H50S, the thickening time of cement slurry decreases with the increase of temperature, and the relationship between them is basically linear; under the same temperature condition, the thickening time of cement slurry increases with the increase of ZOC-H50S dosage. It can be seen from Figure 3 that there is no "bulge" and "twinkling" and other abnormal phenomena in the thickening process of 4.0% ZOC-H50S cement slurry at 180 ℃ (bottom hole circulating temperature). The trend of consistency curve is stable and the transition time is short, basically showing "right angle" thickening. This is beneficial to prevent oil, gas and water channeling in the annulus, which can meet the cementing requirements of high temperature deep wells. Therefore, ZOC-H50S has good high temperature retarding performance. In addition, the thickening time of cement slurry can be effectively adjusted by adjusting the dosage of ZOC-H50S according to different cementing requirements.

In order to further observe the high temperature resistance of ZOC-H50S, differential scanning calorimeter 204f1 and thermogravimetric analyzerTGA-Q500 were used to analyze the high temperature resistance of ZOC-H50S. The results of DTA show that the maximum melting peak appears at 323.7 ℃. According to the analysis of TGA results, the mass loss of ZOC-H50S is 3.4%, 37.8% and 5.3% respectively in the temperature range of 16 ~ 266 ℃, 266 ~ 398 ℃ and 398 ~ 450 ℃. Therefore, when the temperature is higher than 266 ℃, ZOC-H50S has obvious heat change and mass loss, which indicates that the molecular structure of ZOC-H50S is stable and has good high temperature resistance.

3.2 salt resistance

In order to adapt to different formation environment, the retarder should not only have good high temperature retarding performance, but also have good salt resistance. Table 2 shows the test results of thickening time of cement slurry with different salt content and ZOC-H50S dosage at 130 ℃. It can be seen that the thickening time of cement slurry with 8% salt content is basically the same as that of fresh water cement slurry (salt content is 0); the thickening time of cement slurry with 15% salt content is longer than that of fresh water cement slurry, and the thickening time increases with the increase of ZOC-H50S dosage. This may be because salt solution is a kind of strong electrolyte, and strong electronegativity C1 ¯ is coated on the surface of cement particles, which destroys the reversible equilibrium state of water molecules and partly "shields" the contact between water and cement particles, thus making the cement slurry thickening time longer. Other retarders also have the phenomenon that the thickening time of brine slurry is longer than that of fresh water cement slurry. Figure 4 shows the thickening curve of cement slurry with 2.2% ZOC-H50S (15% salt content) at 130 ℃. It can be seen that the consistency curve is stable, without "bulge" and "core" phenomenon, short transition time and basically "right angle" thickening. Therefore, ZOC-H50S has good salt resistance and can be used in cementing operation of saline mud system.

Table 2: salt resistance evaluation results of ZOC-H50S

Figure 4: thickening curve of cement slurry with 2.2% ZOC-H50S (15% salt content) at 130 ℃

3.3 strength development of cement slurry containing ZOC-H50S under large temperature difference

Table 3 shows the strength development of different cement slurry systems under different top and bottom temperature differences. It can be seen that the compressive strength is more than 20MPa after curing at different bottom hole static temperature for 24h after thickening time is more than 300min. Curing at different top temperatures showed good early strength: the strength of cement slurry with 8% salt content (No. 10 cement sample) was basically the same as that of fresh cement slurry (No. 5 cement sample); the cement slurry with cement content of 15% (11 cement sample) developed slowly at low temperature, but the strength after 72h was greater than 7.5MPa. Figure 5 shows the static gel strength development curve of fresh water cement slurry with ZOC-H50S dosage of 2.0% at 70 ℃. It can be seen that the strength of the cement slurry starts to develop rapidly at 20h, reaches above 14MPa at 28h, and exceeds 30MPa at 96h, and then it still tends to increase. Therefore, the slurry system containing ZOC-H50S can be used to solve the problem of super retarding of cement slurry at the top of long cementing section.

Table 3: strength development of cement slurry under different top and bottom temperature difference

Figure 5: static gel strength development curve of fresh water cement slurry with ZOC-H50S dosage of 2.0% at 70 ℃

3.4 performance of low density cement slurry containing ZOC-H50S

At present, some domestic oilfields are faced with the problems of long cementing section cementing in deep wells and long cementing section cementing with low pressure and easy leakage. Because of the large temperature difference between the upper and lower parts of the long cement column in the sealing section, the formation pressure bearing capacity is low, and the leakage is easy to occur during cementing. The application of double-stage cement slurry cementing technology has certain risks and limitations, so the low-density cement slurry system should be adopted. The performance of four kinds of low density cement slurry systems with ZOC-H50S dosage of 1.8% were evaluated (see Table 4). The bottom hole circulation temperature was 130 ℃ and the top temperature was 30 ℃. The results show that the fluidity of low-density cement slurry containing ZOC-H50S is 21-23cm, the thickening time is adjustable, and the slurry has good stability. When the slurry returns to the top temperature of 30 ℃ once, the strength is more than 7MPa in 96h, which can meet the requirements of cementing operation.

Table 4: performance of low density cement slurry containing ZOC-H50S

3.5 applicability evaluation of cement slurry containing ZOC-H50S

Table 5 shows the performance of cement slurry system with different ZOC-H50S dosage under different bottom hole circulation temperature. It can be seen that under different bottom hole circulation temperature, the fluidity of slurry with different density containing ZOC-H50S is 20 ~ 23cm, API filtration rate can be controlled within 100ml, thickening time is adjustable, transit time is short, basically "right angle" thickening, and the top strength of cement slurry column develops well under large temperature difference. Therefore, ZOC-H50S is suitable for a wide range of temperature, and is suitable for high and low density cement slurry system. The slurry containing ZOC-H50S has good comprehensive performance, and is easy to adjust and control, which can meet the requirements of cementing operation in long cementing section.

Table 5: performance of slurry systems with different ZOC-H50S dosages at different bottom hole circulation temperatures