| 摘要 |
A method and apparatus for generating foam cement and placing foam cement in an annulus between a casing and a wellbore. The method includes the steps of displacing cement downwardly in the casing and injecting a gas, preferably nitrogen, into the cement at a predetermined location downhole in the casing. The nitrogen may be injected through a ported sub. The ported sub may be connected in a tubing string that is lowered in the casing. The ported sub has a plurality of ports, which may have nozzles connected therein, that communicate a central opening through the ported sub with an annulus between the ported sub and the casing. The rate at which nitrogen is injected into the cement preferably increases from a leading edge of the cement to a trailing edge of the cement so that a consistent foam cement quality is achieved.
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