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A method and a tandem spacer consisting of an aqueous lead spacer fluid and an aqueous tail spacer fluid for displacing a drilling fluid from an annular space in a wellbore with a cement slurry is disclosed. The aqueous lead spacer fluid and the aqueous tail spacer fluid are formulated to minimize m

A method and a tandem spacer consisting of an aqueous lead spacer fluid and an aqueous tail spacer fluid for displacing a drilling fluid from an annular space in a wellbore with a cement slurry is disclosed. The aqueous lead spacer fluid and the aqueous tail spacer fluid are formulated to minimize mixing between a displaced drilling fluid and a cement slurry and to clean contaminants from the annular space.

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[ I claim:] [10.]10. A method for displacing a drilling fluid from an annular space between the inner surface of a wellbore and the outer surface of a casing positioned in the wellbore with a cement slurry, the method comprising:a) injecting a spacer fluid consisting essentially of:1) an aqueous lea

[ I claim:] [10.]10. A method for displacing a drilling fluid from an annular space between the inner surface of a wellbore and the outer surface of a casing positioned in the wellbore with a cement slurry, the method comprising:a) injecting a spacer fluid consisting essentially of:1) an aqueous lead spacer fluid designed to clean an upper hole section and containing from about 0.5 to about 10 weight percent of a surfactant consisting essentially of from about 10 to about 90 mole percent of at least one alkyl polyglycoside containing alkyl groups containing from about 4 to about 20 carbon atoms and having an oligomerization number from 1 to about 12 and from about 90 to about 10 mole percent of at least one ethoxylated alcohol containing alkyl alcohols containing from about 6 to about 16 carbon atoms and from about 2 to about 8 ethylene oxide groups per molecule of alkyl alcohol; and,2) an aqueous tail spacer fluid designed to clean a bottom hole space and containing from about 0 to about 10 weight percent of a surfactant consisting essentially of from about 30 to about 100 mole percent of at least one alkyl polyglycoside containing alkyl groups containing from about 4 to about 20 carbon atoms and having an oligomerization number from about 1 to about 12 and up to about 70 mole percent of at least one ethoxylated alcohol containing alkyl alcohols containing from about 6 to about 16 carbon atoms and from about 2 to about 8 ethylene oxide groups per molecule of monofunctional alkyl alcohol;b) injecting the cement slurry; andc) injecting a chaser fluid in an amount sufficient to displace the drilling fluid and the spacer fluid from the casing and a selected portion of the annular space with the cement slurry.