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Basic Knowledge
5.3 Retarder
  • Detailed description

In the depth of 1830 ~ 7620 m, the borehole static temperature is about 76.7 ~ 260. In order to prevent the slurry setting too fast, retarder is needed to add into it. If does not use retarder, these basic cement only can be used safely up to the depth of 2438 meters, and with the increasing of temperature, the slurry thicken time will shorten. The deeper the well is and the higher the temperature is, the faster the slurry sets. So in deep well work, retarder must be added, and other admixture of supporting should be used.
According to different application temperature, retarder can be divided into moderate temperature retarder and high temperature retarder. For example, kelioil engineering materials and technology Co., LTD CH210 series moderate temperature retarder’s using temperature is from 55 to 110℃. The using temperature high temperature retarder CH310L and high temperature retarder CH510S powder (patent no. : 201110229274.4) is from 90 ~ 150℃. There is no general retarder suitable for both high and moderate temperature at present.
The retarder technical requirements:
The evaluation method for oil cement additives-- part 1: retarder: has the following performance requirement to the slurry with retarder:


Table 3-1 the properties of cement slurry with CH series of retarders

Item

Technical index

Initial consistency,Bc

≤30

Transition time from 40 Bc to100Bc,min

≤40

Shape of thicken-time curve

Normal

Free fluid, %

≤1.4

24hcompressive strength,MPa

≥14

Adjustability of thicken time

Adjustable

Dosage sensitivity coefficient (optional)

0.1~3.0

Deviation rate of thickening-time at 5℃ increment (optional),%

≤20

The retarder as a high quality product must meet the following requirements:
1. Thickening-time adjustability. The thicken time can be prolonged by increasing the dosage. Usually there is a requirements of the thicken time should be in 120 min-600 min adjustable. Some retarder’s dosage increase but the thicken time has no increase or increase a little. This is because the thicken time of this retarder in this experiment temperature can not be adjusted.
2. Thicken time is long enough. The slurry thicken time can be long enough to meet with the longer time cementing requirements
3. Shape of thicken-time curve. The shape of thicken-time curve should be normal. The thick time of quality fluid loss additive products should be within 10 min when the consistency increasing from 40 Bc to100 Bc.
4. Have no effect to the consistency. Usually moderate temperature retarder will increase the viscosity of the slurry. High temperature retarder will reduce slurry consistency, the high quality retarder have little impact on the slurryr viscosity.