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8
Sulfide
Testing
The concentration of soluble sulfides, including hydrogen sulfide (H
2
S),
sulfide (S
-2
), and (HS
-
) ions may be determined with the Garrett Gas Train.
Mud filtrate is acidified in the gas train, which converts all of the sulfides to
H
2
S. The H
2
S is then evolved by bubbling an inert carrier gas, usually carbon
dioxide (CO
2
), through the sample. The gas train separates the gas from the
liquid. The gas stream is then passed through a Dräger tube which responds
to H
2
S by darkening along its length. The length of the darkened strip is
proportional to the total sulfides in the mud filtrate. The low range Dräger tube
turns from white to brownish-black and the high range tube turns from pale
blue to jet black. No common drilling fluid contaminant will cause these color
changes. Lead acetate paper disks may be used qualitatively to determine
the presence or absence of sulfides. If the presence of sulfide is indicated by
a darkening of the lead acetate paper, a Dräger tube may then be used for
quantitative analysis.
