Test for free water is only necessary for class G and H cements. The purpose of free water control is if you have free water break out of the slurry and your well is deviated, then the water can rise up, breakout and form a channel on the high side of the well. If it does that and can communicate between the zone of high pressure and the zone of lower pressure then the only force holding the higher pressure zone back would be the way of the water which is significantly less than the way that the cement and it allows flow after cementing which is one of the major difficulties in cementing. In the test for free water, the cement slurry is stored in a consistometer for 12 minutes. It's allowed to stand for a period of time. Then remixed it in the blinder for 35 seconds and placed in a graduated cylinder for 2 hours.
Since free water volume can be significantly affected by hole angle, free water tests for deviated wells are often conducted with a graduated cylinder placed in various positions in addition to the API specified vertical position. Supernatant water is then measure; its volume should be less than 3.5 milliliters for 250 millimeters of initial slurry.
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