Page 213 - Well Control for Completions and Interventions

206 Well Control for Completions and Interventions

5.7 BRINE CLARITY AND SOLIDS CONTENT

Minimizing formation damage relies on having a clean (solids free)
brine. This is especially important if the brine is expected to come into
contact with the reservoir. Brine clarity and solids content is measured at
the wellsite. The three most common and useful measures of brine clean-
liness are turbidity, volume percent of solids, and particle size distribution.
Turbidity meters work by shining a light (laser) through a fluid sample
and observing the amount of scattering or reflection. Turbidity, a measure
of the cloudiness of a fluid, is recorded in Nephelometric Turbidity Units
(NTUs).
Five NTUs are just noticeable by the eye, while 50 100 NTUs are
often used as an indication of brine clarity. More stringent NTU values
are used for some completion and intervention fluids. For example, brines
used for open hole gravel packing and frac-packs normally require very
low limits, with some operating companies setting targets as low as
5NTU. However, an absolute reliance on NTUs as a measure of fluid
cleanliness can be misleading. This is because the fluid sample may be dis-
colored while being largely free of solids. Moreover, measuring NTU
gives no indication of particle size or distribution (Fig. 5.6).

Figure 5.6 Low solids content, but NTU value?