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Basic Knowledge
7.4 Short thickening time cement slurry system
  • Detailed description

In the process of adjusting well cementing, water channeling and water leaching is one of the worst problems. In the initial stage of pumping slurry, the annual cement as a actual fluid can transit pressure efficiently. And when the slurry produces gel strength and loses weight, annular stable pressure will decrease to zero or negative value. And the annular cement slurry only lays on itself to prevent channeling. This stage is the most weak in the cementing project. Generally, the time of the gel strength developing from 100lb/100ft2 to 500 lb/100ft2 is the transition gel period. The shorter the transition gel period is the ability of cement slurry controlling the oil and water channeling is stronger. So shorten this stage is necessary.
Another reason that the annular pressure decreases is the volume shrinkage caused by fluid loss and hydration. Generally, the Portland cement’s absolute volume shrinkage rate is 2.3-5.1%. if the gel strength is not high enough, the pressure decreasing caused by fluid loss and hydration shrinkage can be complemented partly by the cement slurry free fall. When the gel strength becomes strong enough to support itself, the volume shrinkage caused by the fluid loss and hydration can reduce the annular stable pressure. In order to increase the unti-channeling ability of cement slurry, you can reduce the fluid loss of cement slurry or add expansion materials.

    The main character of short thickening time cement slurry has short transition time. This cement slurry can transform quickly from the flow state to the gel state. That can improve the cementing quality efficiently. This type cement slurry can inform impermeable membrane in the hydration process and prevent the slurry column from water. At the same time, the good adhesion and cohesiveness can prevent the slurry gel at a certain extend. It has the advantages of accelerating, early strength, short transition time. The general transition time (from 40Bc to 100Bc) is shorter than 10 min. It can form gel quickly and satisfy the cementing requirements.