(1) The long cementing section increases the temperature difference between the top and bottom of the well (for example, the length of the cementing section is 1500m, if the geothermal gradient is 3 ℃ / 100M, the temperature difference of the cementing section is up to 45 ℃), which leads to a large difference in the waiting time between the top and bottom of the cement slurry column in the long cementing section, and sometimes the top cement slurry will solidify after a few days, which seriously affects the follow-up operation.

(2) The long sealing section increases the pressure of the cement slurry column at the bottom of the well, which puts forward very high requirements for the pressure bearing capacity of the formation. If the formation fracture pressure is small, there is the risk of pressure loss formation.

(3) The cement slurry sealing section is long. In order to improve the displacement efficiency, the flow velocity of cement slurry in the annular flow process is larger (about 2m3 / min), and the annular flow resistance is also increased. Therefore, it is easier to form high overbalance pressure and cause leakage in the cementing process. Moreover, the increase of sealing length has a great influence on the fluidity and water loss of cement slurry.

To sum up, the traditional low-density cement slurry or staged cementing technology has been difficult to meet the requirements of safety and quality of long cementing section. However, there are few researches on low density cement slurry which can be used for long cementing section in China; The cost of similar systems available abroad is 17.891. Therefore, it is necessary to develop broadband retarder and low density cement slurry system which can be used in long cementing section to meet the urgent need of production.