An extensive laboratory program showed that foamed cement was the only technically feasible solution to prepare a "floating" cement plug for solving severe lost circulation problems in big caverns. The technique had, however, to be adapted to fit well conditions that are relatively unusual in the oil field: the cement slurry should not become diluted and destabilized upon exiting the drill pipe and entering the 60-plus inches wellbore and the huge caves, several feet in radius, both filled with sea water. Moreover, the foam had to remain stable, even when surrounded by large volume of water, until cement setting.

Therefore a technique of using "protective" fluids was devised. In addition, logistics dictated the use of compressed air rather than nitrogen to prepare the foamed slurry. Therefore special gas metering and regulation devices were used for the first time in the oil field in order to automate the process and get a perfect control of the slurry density whatever the slurry mixing and pumping rates.

Before field implementation, the metering and regulation device was successfully yard tested, the gas phase being supplied by nitrogen bottles. The successful field implementation with air compressors, together with the "protective" fluid technique to combat lost circulation in loose coral reef and in highly fractured dolomitic formation, is described.*

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