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Basic Knowledge
5.4 Accelerator
  • Detailed description

The role of the accelerator is to shorten the consistency time, and accelerates the hardening of cement, improves the early strength of set cement. It is used in shallow wells and low temperature strata, etc. Through the use of accelerator, the strength of the basic slurry can reach to 3.5 MPa in 4 h and meet the requirements of the second spud.
The accelerator is one of the earliest use of admixture, common are calcium chloride. Calcium chloride is strong water absorption material, in cementing the more used is no water flake calcium chloride, its general dosage is 2 ~ 4%. The most common organic compounds acceletator is triethanolamine. The triethanolamine is a kind of surface active agent, mixed with cement, and plays the role of catalyst in the process of cement hydration. It can accelerate C3A hydration and ettringite formation. But if use calcium chloride monomer or triethanolamine monomer only, its function is not good. So the commercial compound accelerator appeared. It includes chlorine ionic accelerator and no chlorine ionic accelerator two types. Only from the performance, the chlorine ion acceletator performance is better than no chlorine ion one, but chlorine ion accelerator on the casing caused great corrosion, and shorten the oil and gas wells mining life.
The acceletator’s technical requirements:
The evaluation method for oil cement additives-- part 4: accelerator: has the following performance requirement to the slurry with accelerator:

Table 4-1 the properties of cement slurry with CA series of accelerator

Item

Technical index

The ratio of thickening time(32℃,8.3MPa)

≤0.5

The initial consistency(32℃,8.3MPa),Bc

≤30

6hcompressive strength(39℃,normal)Mpa

≥4.0

The ratio of 24h compressive strength(39℃,normal)

≥1.0

 Note:
1:The ratio of thickening time is the ratio of the thickening time of neat slurry and the thickening time of slurry with accelerator.
2:The ratio of compressive strength is the ratio of compressive strength of neat slurry and the compressive strength of slurry with accelerator.
3:In the brackets is the test condition.

Quality accelerator should satisfy the following requirements:

1. Using temperature is low, it still can accelerate thickening under very low temperature,

2. The early strength develops quickly.