Effect of Mixing Energy Levels During Batch Mixing of Cement Slurries
- A.P. Hibbert (BP Exploration) | D.J. Kellingray (BP Exploration) | Benoit Vidick (Schlumberger Dowell)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 1995
- Document Type
- Journal Paper
- 49 - 52
- 1995. Society of Petroleum Engineers
- 1.14 Casing and Cementing, 4.3.1 Hydrates, 1.14.3 Cement Formulation (Chemistry, Properties), 4.3.4 Scale, 5.2 Reservoir Fluid Dynamics
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The properties of batch-mixed slurries prepared in a series of yard tests using full-scale equipment are compared with laboratory tests on the same materials. Dramatic differences have been observed between conventional laboratory tests and field scale properties.
By splitting the batch-mixing process into distinct steps, a laboratory method is tested against the observed differences.
It is shown that mixing energy is an important parameter in slurry design and that energy levels substantially above the conventional API laboratory mixing energy may degrade slurry properties such as pumping time.
Batch mixing of slurries for critical jobs is a common practice when the size of the job allows, (say), less than 100 bbl. Many different types and size of batch mixer are available to cope with offshore restrictions and batch mixing offers the assurance of good quality control of the slurry prior to pumping. The density can be controlled within tight limits and the slurry is fully homogenized and can even be subjected to testing prior to committing to pumping.
Although physical and chemical aspects of mixing have been investigated before, there is little data on the effect of batch mixers on slurry properties and no industry accepted laboratory test procedure to design such slurries to account for the numerous parameters involved. Laboratory testing invariably follows the API procedure for thickening time and, although this may be adequate in some cases, it cannot universally predict field behaviour.
The mixing, homogenization, pumping and displacement of the cement slurry all play a part in determining the hydration and thickening behaviour. The relative contributions from each part of the process need to be understood if failures are to be avoided. In general, it has been found that increasing the mixing energy up to the value experienced in the API laboratory test is a good thing. Many slurry properties are improved.
At levels of mixing energy greater than the API value, properties may degrade. The actual behaviour will depend on the type of slurry design, the brand of the cement as well as its API classification and, in the case of batch mixing, the volume mixed and the amount of shear energy delivered during mixing and homogenization. Again, the process needs to be viewed as a whole. Surface lines can provide extra mixing energy as, indeed, can pumping through coiled tubing. Often these contributions may not have a significant impact on slurry properties but do need to be quantified and understood. In batch mixing of relatively small volumes of slurry (10 bbl), profound changes can occur in properties compared with conventional laboratory testing.
This paper describes a series of yard tests using full-scale equipment coupled with considerable laboratory testing of samples of slurry taken from the yard and also mixed in the laboratory using identical material.
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