STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

710 Drilling and Well Completions
Table 4-65
Material Requirements for KCI Solutions (60°F)
Density Fresh Water Potassium Chloride
PDSI galhbl final lblbbl final
8.42 41.7 7.0
8.64 41 .O 21.1
8.86 40.2 35.2
9.09 39.4 53.6
9.32 38.6 70.5
9.56 37.6 88.2
9.78 36.7 105.0
problems for squeeze cementing, but is removed with production and increasing
temperatures.
Starch is also used for fluid loss control. It does not provide carrying capacity;
therefore other polymers are required. Although starch is relatively cheap, it has
two serious limitations: (1) starch is subject to fermentation, and (2) it causes
significant permeability reduction due to plugging.
The synthetic polymers commonly used in completion fluids are HEC and
Xanthan gum (XC Polymer). Xanthan gum is a biopolymer that provides good
rheological properties and that is completely soluble in HCl. HEC-hydroxyethyl
cellulose is currently the best viscosifer. It gives good carrying capacity, fluid
loss control, and rheology; it is completely removable with hydrochloric acid.
The effect of HCl on the restored permeability for HEC completion fluid is
shown in Figure 4-124 and Table 4-68 [36]. It can be noticed that 100% of the
original core permeability was restored by displacing acid-broken HEC with
brine. The comparison of permeability damage caused by different polymers is
given in Table 4-69 [36].
The bridging materials commonly used in completion and workover fluids are
ground calcium carbonate, gilsonite, and asphalt. These materials should
demonstrate uniform particle size distribution and be removable by acid or by
backflow. Their mesh size should enable them to flush through the gravel pack;
a mesh size of 200 is considered satisfactory for most completions. Calcium
carbonate bridging materials are completely soluble in hydrochloric acid. Resins
give effective bridging; they are soluble in oil solutions (2% by volume oil).
A typical formulation of a brine-polymer completion f hid might include 8.5
to 11 lb/gal salt water solution (NaCl, CaCl,, KCl, or a mixture), 0.25 to 1.0
lb/bbl polymer and 5 to 15% calcium carbonate.
Density control in brine-polymer systems can be achieved with salt solutions
or with weighting materials. When mixing heavy brine completion fluids, the
following factors should be considered:
1. Cost-heavy brines are very expensive.
2. Downhole temperature effect on the brine density-Table 4-69 [26].
3. Crystallization temperature-Figure 4-125 [37].
4. Corrosion-various salts have different acidities (pH of brine can be controlled
with lime, caustic soda, or calcium bicarbonate).
5. Safety-burns from heat generated while mixing and skin damage should
be prevented.
6. Toxicity-dispersal cost depends on type of salt and concentration.