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Basic Knowledge
5.5 Dispersant
  • Detailed description

Adding dispersant into the cement slurry can improve its liquidity, the slurry with dispersant has low viscosity. And it can reach turbulence at a lower pump pressure, so it need less power and can reduce the well leakage and slurry premature dehydration. The usage of some fluid-loss additive will lead to the slurry system viscosity increasing. In order to improve the pump, it is need to add the dispersant into the slurry. The interaction between the oil well cement particles depends on the surface charge distribution. The dispersant is to get the right theological properties by adjusting the particles surface charge.
Now commonly used dispersant have the following types:
1. The sulfonated acetone formaldehyde condensation polymer dispersant. This kind dispersant has resistance to the high temperature and has good compatibility with other additives. And at the same time the cost is low. But it has poor applicability with all kind cements.  
2. Naphthalene dispersant. This kind dispersant only can be used at low and middle temperature but its cost is low.
3. Polycarboxylate dispersant. This kind dispersant is commonly used in the building cement. In cementing industry it is less, the dosage is low.
4. AMPS copolymerization dispersant. This kind dispersant has a good resistance to the high temperature and salt and also has a good compatibility with all kind cement. But the cost is high.
The dispersant technical requirements:

The evaluation method for oil cement additives-- part 3: dispersant: has the following performance requirement to the slurry with dispersant:

Table 5-1 the properties of cement slurry with CF series of moderate temperature dispersant

Item

Technical index

The ratio of thickening time (52℃, 35.6Mpa)

1.0~2.0

The ratio of compressive strength (67℃,normal pressure)

≥0.9

Rheological Properties (52℃,normal pressure)

≥0.55

K,Pa·sn

≤0.50

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

Table 5-2 the properties of cement slurry with CF series of high temperature dispersant

Item

Technical index

The ratio of thickening time(85℃,70.3Mpa)

1.0~2.0

The ratio of compressive strength (110℃,21MPa)

≥0.8

Rheological Properties (85℃,normal pressure)

≥0.50

K,Pa·sn

≤0.50

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

Quality dispersant should satisfy the following requirements:

1. Having good compatibility with all kinds cement.

2. Application temperature rang is wide.