STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

708 Drilling and Well Completions
oil, and that they do not oil or wet the reservoir rock. The usual treatment
includes a small amount (0.1%) of the proper surfactant.
Seawater or bay water base completion fluids should be treated with
bactericides to inhibit bacterial growth. Since these fluids usually contain clays,
inhibition with NaCl or KCl may be necessary to prevent plugging of the
producing formation.
Prepared saltwater completion fluids are made of fresh surface water, with
sufficient salts added to produce the proper salt concentration. Usually, the
addition of 5 to 10% NaCl, 2% CaCl,, or 2% KCl is considered satisfactory for
clay inhibition in most formations. Sodium chloride solutions have been
extensively used for many years as completion fluids; these brines have densities
up to 10 lb/gal. Calcium chloride solutions may have densities up to 11.7 lb/
gal. The limitations of CaCl, solutions are (1) flocculation of certain clays,
causing permeability reduction, and (2) high pH (10 to 10.5) that may
accelerate formation clays dispersion. In such cases, CaCl2-based completion
fluids should be replaced with potassium chloride solutions. Other clear brines
can be formulated using various salts over wide range of densities, as shown in
Figure 4-123 [28].
I
I . I I
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Idbrine P*
I I 1 I 1
*Patents applied for by I.D.F.
BRINE DENSITY PW
Figure 4-123. Salts used in clear brine completion fluids of various densities
[28]. (Courtesy International Drilling Fluids, Inc.)